• SDL2来源分析3:渲染(SDL_Renderer)


    =====================================================

    SDL源代码分析系列文章上市:

    SDL2源码分析1:初始化(SDL_Init())

    SDL2源码分析2:窗体(SDL_Window)

    SDL2源码分析3:渲染器(SDL_Renderer)

    SDL2源码分析4:纹理(SDL_Texture)

    SDL2源码分析5:更新纹理(SDL_UpdateTexture())

    SDL2源码分析6:拷贝到渲染器(SDL_RenderCopy())

    SDL2源码分析7:显示(SDL_RenderPresent())

    SDL2源码分析8:视频显示总结

    =====================================================


    上一篇文章分析了SDL中创建窗体的函数SDL_CreateWindow()。这篇文章继续分析SDL的源码。

    本文分析SDL的渲染器(SDL_Renderer)。



    SDL播放视频的代码流程例如以下所看到的。

    初始化: 
    SDL_Init(): 初始化SDL。

     
    SDL_CreateWindow(): 创建窗体(Window)。 
    SDL_CreateRenderer(): 基于窗体创建渲染器(Render)。 
    SDL_CreateTexture(): 创建纹理(Texture)。

     

    循环渲染数据: 
    SDL_UpdateTexture(): 设置纹理的数据。

     
    SDL_RenderCopy(): 纹理复制给渲染器。 

    SDL_RenderPresent(): 显示。

    上篇文章分析了该流程中的第2个函数SDL_CreateWindow()。

    本文继续分析该流程中的第3个函数SDL_CreateRenderer()。

    SDL_Renderer

    SDL_Renderer结构体定义了一个SDL2中的渲染器。假设直接使用SDL2编译好的SDK的话。是看不到它的内部结构的。

    有关它的定义在头文件里仅仅有一行代码。例如以下所看到的。

    /**
     *  rief A structure representing rendering state
     */
    struct SDL_Renderer;
    typedef struct SDL_Renderer SDL_Renderer;

    在源码project中能够看到SDL_Renderer的定义,位于renderSDL_sysrender.h文件里。

    它的定义例如以下。

    /* Define the SDL renderer structure */
    struct SDL_Renderer
    {
        const void *magic;
    
    
        void (*WindowEvent) (SDL_Renderer * renderer, const SDL_WindowEvent *event);
        int (*GetOutputSize) (SDL_Renderer * renderer, int *w, int *h);
        int (*CreateTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
        int (*SetTextureColorMod) (SDL_Renderer * renderer,
                                   SDL_Texture * texture);
        int (*SetTextureAlphaMod) (SDL_Renderer * renderer,
                                   SDL_Texture * texture);
        int (*SetTextureBlendMode) (SDL_Renderer * renderer,
                                    SDL_Texture * texture);
        int (*UpdateTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
                              const SDL_Rect * rect, const void *pixels,
                              int pitch);
        int (*UpdateTextureYUV) (SDL_Renderer * renderer, SDL_Texture * texture,
                                const SDL_Rect * rect,
                                const Uint8 *Yplane, int Ypitch,
                                const Uint8 *Uplane, int Upitch,
                                const Uint8 *Vplane, int Vpitch);
        int (*LockTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
                            const SDL_Rect * rect, void **pixels, int *pitch);
        void (*UnlockTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
        int (*SetRenderTarget) (SDL_Renderer * renderer, SDL_Texture * texture);
        int (*UpdateViewport) (SDL_Renderer * renderer);
        int (*UpdateClipRect) (SDL_Renderer * renderer);
        int (*RenderClear) (SDL_Renderer * renderer);
        int (*RenderDrawPoints) (SDL_Renderer * renderer, const SDL_FPoint * points,
                                 int count);
        int (*RenderDrawLines) (SDL_Renderer * renderer, const SDL_FPoint * points,
                                int count);
        int (*RenderFillRects) (SDL_Renderer * renderer, const SDL_FRect * rects,
                                int count);
        int (*RenderCopy) (SDL_Renderer * renderer, SDL_Texture * texture,
                           const SDL_Rect * srcrect, const SDL_FRect * dstrect);
        int (*RenderCopyEx) (SDL_Renderer * renderer, SDL_Texture * texture,
                           const SDL_Rect * srcquad, const SDL_FRect * dstrect,
                           const double angle, const SDL_FPoint *center, const SDL_RendererFlip flip);
        int (*RenderReadPixels) (SDL_Renderer * renderer, const SDL_Rect * rect,
                                 Uint32 format, void * pixels, int pitch);
        void (*RenderPresent) (SDL_Renderer * renderer);
        void (*DestroyTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
    
    
        void (*DestroyRenderer) (SDL_Renderer * renderer);
    
    
        int (*GL_BindTexture) (SDL_Renderer * renderer, SDL_Texture *texture, float *texw, float *texh);
        int (*GL_UnbindTexture) (SDL_Renderer * renderer, SDL_Texture *texture);
    
    
        /* The current renderer info */
        SDL_RendererInfo info;
    
    
        /* The window associated with the renderer */
        SDL_Window *window;
        SDL_bool hidden;
    
    
        /* The logical resolution for rendering */
        int logical_w;
        int logical_h;
        int logical_w_backup;
        int logical_h_backup;
    
    
        /* The drawable area within the window */
        SDL_Rect viewport;
        SDL_Rect viewport_backup;
    
    
        /* The clip rectangle within the window */
        SDL_Rect clip_rect;
        SDL_Rect clip_rect_backup;
    
    
        /* The render output coordinate scale */
        SDL_FPoint scale;
        SDL_FPoint scale_backup;
    
    
        /* The list of textures */
        SDL_Texture *textures;
        SDL_Texture *target;
    
    
        Uint8 r, g, b, a;                   /**< Color for drawing operations values */
        SDL_BlendMode blendMode;            /**< The drawing blend mode */
    
    
        void *driverdata;
    };

    通过代码能够看出当中包括了一个“渲染器”应该包括的各种属性。

    这个结构体中的各个变量还没有深入研究,暂不具体分析。

    以下来看看怎样创建这个SDL_Renderer。


    SDL_CreateRenderer()

    函数简单介绍

    SDL中使用SDL_CreateRenderer()基于窗体创建渲染器。SDL_CreateRenderer()原型例如以下。
    SDL_Renderer * SDLCALL SDL_CreateRenderer(SDL_Window * window,
                                                   int index, Uint32 flags);

    參数含义例如以下。

    window : 渲染的目标窗体。

    index :打算初始化的渲染设备的索引。

    设置“-1”则初始化默认的渲染设备。

    flags :支持以下值(位于SDL_RendererFlags定义中)

        SDL_RENDERER_SOFTWARE :使用软件渲染

        SDL_RENDERER_ACCELERATED :使用硬件加速

        SDL_RENDERER_PRESENTVSYNC:和显示器的刷新率同步

        SDL_RENDERER_TARGETTEXTURE :不太懂

    返回创建完毕的渲染器的ID。假设创建失败则返回NULL。


    函数调用关系图

    SDL_CreateRenderer()关键函数的调用关系能够用下图表示。


    上述图片不太清晰,相冊里面上传了一份原始的大图片:

    http://my.csdn.net/leixiaohua1020/album/detail/1793385

    打开上述相冊里面的图片,右键选择“另存为”就可以保存原始图片。



    源码分析

    SDL_CreateRenderer()的源码位于renderSDL_render.c中,例如以下所看到的。

    SDL_Renderer * SDL_CreateRenderer(SDL_Window * window, int index, Uint32 flags)
    {
    #if !SDL_RENDER_DISABLED
        SDL_Renderer *renderer = NULL;
        int n = SDL_GetNumRenderDrivers();
        const char *hint;
    
    
        if (!window) {
            SDL_SetError("Invalid window");
            return NULL;
        }
    
    
        if (SDL_GetRenderer(window)) {
            SDL_SetError("Renderer already associated with window");
            return NULL;
        }
    
    
        hint = SDL_GetHint(SDL_HINT_RENDER_VSYNC);
        if (hint) {
            if (*hint == '0') {
                flags &= ~SDL_RENDERER_PRESENTVSYNC;
            } else {
                flags |= SDL_RENDERER_PRESENTVSYNC;
            }
        }
    
    
        if (index < 0) {
            hint = SDL_GetHint(SDL_HINT_RENDER_DRIVER);
            if (hint) {
                for (index = 0; index < n; ++index) {
                    const SDL_RenderDriver *driver = render_drivers[index];
    
    
                    if (SDL_strcasecmp(hint, driver->info.name) == 0) {
                        /* Create a new renderer instance */
                        renderer = driver->CreateRenderer(window, flags);
                        break;
                    }
                }
            }
    
    
            if (!renderer) {
                for (index = 0; index < n; ++index) {
                    const SDL_RenderDriver *driver = render_drivers[index];
    
    
                    if ((driver->info.flags & flags) == flags) {
                        /* Create a new renderer instance */
                        renderer = driver->CreateRenderer(window, flags);
                        if (renderer) {
                            /* Yay, we got one! */
                            break;
                        }
                    }
                }
            }
            if (index == n) {
                SDL_SetError("Couldn't find matching render driver");
                return NULL;
            }
        } else {
            if (index >= SDL_GetNumRenderDrivers()) {
                SDL_SetError("index must be -1 or in the range of 0 - %d",
                             SDL_GetNumRenderDrivers() - 1);
                return NULL;
            }
            /* Create a new renderer instance */
            renderer = render_drivers[index]->CreateRenderer(window, flags);
        }
    
    
        if (renderer) {
            renderer->magic = &renderer_magic;
            renderer->window = window;
            renderer->scale.x = 1.0f;
            renderer->scale.y = 1.0f;
    
    
            if (SDL_GetWindowFlags(window) & (SDL_WINDOW_HIDDEN|SDL_WINDOW_MINIMIZED)) {
                renderer->hidden = SDL_TRUE;
            } else {
                renderer->hidden = SDL_FALSE;
            }
    
    
            SDL_SetWindowData(window, SDL_WINDOWRENDERDATA, renderer);
    
    
            SDL_RenderSetViewport(renderer, NULL);
    
    
            SDL_AddEventWatch(SDL_RendererEventWatch, renderer);
    
    
            SDL_LogInfo(SDL_LOG_CATEGORY_RENDER,
                        "Created renderer: %s", renderer->info.name);
        }
        return renderer;
    #else
        SDL_SetError("SDL not built with rendering support");
        return NULL;
    #endif
    }

    SDL_CreateRenderer()中最重要的一个函数就是它调用了SDL_RenderDriver的CreateRenderer()方法。通过该方法能够创建一个渲染器。

    环绕着这种方法,包括了一些初始化工作以及一些收尾工作。

    以下针对这个最核心的函数进行分析。
    我们首先来看一下SDL_RenderDriver这个结构体。从字面的意思能够看出它代表了“渲染器的驱动程序”。

    这个结构体的定义例如以下。


    /* Define the SDL render driver structure */
    struct SDL_RenderDriver
    {
        SDL_Renderer *(*CreateRenderer) (SDL_Window * window, Uint32 flags);
    
    
        /* Info about the renderer capabilities */
        SDL_RendererInfo info;
    };

    从代码中能够看出,这个结构体的成员比較简单。包括了一个函数指针CreateRenderer()和一个存储信息的SDL_RendererInfo类型的结构体info。CreateRenderer()是用于创建渲染器的函数,而SDL_RendererInfo则包括了该结构体的一些信息。能够看一下SDL_RendererInfo的定义。
    /**
     *  rief Information on the capabilities of a render driver or context.
     */
    typedef struct SDL_RendererInfo
    {
        const char *name;           /**< The name of the renderer */
        Uint32 flags;               /**< Supported ::SDL_RendererFlags */
        Uint32 num_texture_formats; /**< The number of available texture formats */
        Uint32 texture_formats[16]; /**< The available texture formats */
        int max_texture_width;      /**< The maximimum texture width */
        int max_texture_height;     /**< The maximimum texture height */
    } SDL_RendererInfo;

    在SDL中有一个全局的SDL_RenderDriver类型的静态数组render_drivers,当中存储了SDL支持的全部渲染器。

    该数组定义例如以下。

    static const SDL_RenderDriver *render_drivers[] = {
    #if SDL_VIDEO_RENDER_D3D
        &D3D_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_D3D11
        &D3D11_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_OGL
        &GL_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_OGL_ES2
        &GLES2_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_OGL_ES
        &GLES_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_DIRECTFB
        &DirectFB_RenderDriver,
    #endif
    #if SDL_VIDEO_RENDER_PSP
        &PSP_RenderDriver,
    #endif
        &SW_RenderDriver
    };

    从render_drivers数组的定义能够看出,当中包括了Direct3D,OpenGL。OpenGL ES等各种渲染器的驱动程序。

    我们能够选择几个看一下。
    比如Direct3D的渲染器驱动程序D3D_RenderDriver的定义例如以下(位于renderdirect3dSDL_render_d3d.c)。

    SDL_RenderDriver D3D_RenderDriver = {
        D3D_CreateRenderer,
        {
         "direct3d",
         (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
         1,
         {SDL_PIXELFORMAT_ARGB8888},
         0,
         0}
    };

    能够看出创建Direct3D渲染器的函数是D3D_CreateRenderer()。

    OpenGL的渲染器驱动程序GL_RenderDriver的定义例如以下(位于renderopenglSDL_render_gl.c)。


    SDL_RenderDriver GL_RenderDriver = {
        GL_CreateRenderer,
        {
         "opengl",
         (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
         1,
         {SDL_PIXELFORMAT_ARGB8888},
         0,
         0}
    };

    能够看出创建OpenGL渲染器的函数是GL_CreateRenderer()。


    软件渲染器驱动程序SW_RenderDriver的定义例如以下(位于rendersoftwareSDL_render_sw.c)。
    SDL_RenderDriver SW_RenderDriver = {
        SW_CreateRenderer,
        {
         "software",
         SDL_RENDERER_SOFTWARE | SDL_RENDERER_TARGETTEXTURE,
         8,
         {
          SDL_PIXELFORMAT_RGB555,
          SDL_PIXELFORMAT_RGB565,
          SDL_PIXELFORMAT_RGB888,
          SDL_PIXELFORMAT_BGR888,
          SDL_PIXELFORMAT_ARGB8888,
          SDL_PIXELFORMAT_RGBA8888,
          SDL_PIXELFORMAT_ABGR8888,
          SDL_PIXELFORMAT_BGRA8888
         },
         0,
         0}
    };

    能够看出创建软件渲染器的函数是SW_CreateRenderer ()。


    有关SDL_RenderDriver这个结构体就不再多说了。以下分别看一下Direct3D,OpenGL,Software这三种最常见的渲染器的创建方法。

    1. Direct3D

    Direct3D 的渲染器在创建函数是D3D_CreateRenderer()。该函数位于renderdirect3dSDL_render_d3d.c文件里。首先看一下它的代码。

    SDL_Renderer * D3D_CreateRenderer(SDL_Window * window, Uint32 flags)
    {
        SDL_Renderer *renderer;
        D3D_RenderData *data;
        SDL_SysWMinfo windowinfo;
        HRESULT result;
        const char *hint;
        D3DPRESENT_PARAMETERS pparams;
        IDirect3DSwapChain9 *chain;
        D3DCAPS9 caps;
        DWORD device_flags;
        Uint32 window_flags;
        int w, h;
        SDL_DisplayMode fullscreen_mode;
        int displayIndex;
    
    
        renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
        if (!renderer) {
            SDL_OutOfMemory();
            return NULL;
        }
    
    
        data = (D3D_RenderData *) SDL_calloc(1, sizeof(*data));
        if (!data) {
            SDL_free(renderer);
            SDL_OutOfMemory();
            return NULL;
        }
    
    
        if (!D3D_LoadDLL(&data->d3dDLL, &data->d3d)) {
            SDL_free(renderer);
            SDL_free(data);
            SDL_SetError("Unable to create Direct3D interface");
            return NULL;
        }
    
    
        renderer->WindowEvent = D3D_WindowEvent;
        renderer->CreateTexture = D3D_CreateTexture;
        renderer->UpdateTexture = D3D_UpdateTexture;
        renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
        renderer->LockTexture = D3D_LockTexture;
        renderer->UnlockTexture = D3D_UnlockTexture;
        renderer->SetRenderTarget = D3D_SetRenderTarget;
        renderer->UpdateViewport = D3D_UpdateViewport;
        renderer->UpdateClipRect = D3D_UpdateClipRect;
        renderer->RenderClear = D3D_RenderClear;
        renderer->RenderDrawPoints = D3D_RenderDrawPoints;
        renderer->RenderDrawLines = D3D_RenderDrawLines;
        renderer->RenderFillRects = D3D_RenderFillRects;
        renderer->RenderCopy = D3D_RenderCopy;
        renderer->RenderCopyEx = D3D_RenderCopyEx;
        renderer->RenderReadPixels = D3D_RenderReadPixels;
        renderer->RenderPresent = D3D_RenderPresent;
        renderer->DestroyTexture = D3D_DestroyTexture;
        renderer->DestroyRenderer = D3D_DestroyRenderer;
        renderer->info = D3D_RenderDriver.info;
        renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
        renderer->driverdata = data;
    
    
        SDL_VERSION(&windowinfo.version);
        SDL_GetWindowWMInfo(window, &windowinfo);
    
    
        window_flags = SDL_GetWindowFlags(window);
        SDL_GetWindowSize(window, &w, &h);
        SDL_GetWindowDisplayMode(window, &fullscreen_mode);
    
    
        SDL_zero(pparams);
        pparams.hDeviceWindow = windowinfo.info.win.window;
        pparams.BackBufferWidth = w;
        pparams.BackBufferHeight = h;
        if (window_flags & SDL_WINDOW_FULLSCREEN) {
            pparams.BackBufferFormat =
                PixelFormatToD3DFMT(fullscreen_mode.format);
        } else {
            pparams.BackBufferFormat = D3DFMT_UNKNOWN;
        }
        pparams.BackBufferCount = 1;
        pparams.SwapEffect = D3DSWAPEFFECT_DISCARD;
    
    
        if (window_flags & SDL_WINDOW_FULLSCREEN) {
            if ((window_flags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP)  {
                pparams.Windowed = TRUE;
                pparams.FullScreen_RefreshRateInHz = 0;
            } else {
                pparams.Windowed = FALSE;
                pparams.FullScreen_RefreshRateInHz = fullscreen_mode.refresh_rate;
            }
        } else {
            pparams.Windowed = TRUE;
            pparams.FullScreen_RefreshRateInHz = 0;
        }
        if (flags & SDL_RENDERER_PRESENTVSYNC) {
            pparams.PresentationInterval = D3DPRESENT_INTERVAL_ONE;
        } else {
            pparams.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
        }
    
    
        /* Get the adapter for the display that the window is on */
        displayIndex = SDL_GetWindowDisplayIndex(window);
        data->adapter = SDL_Direct3D9GetAdapterIndex(displayIndex);
    
    
        IDirect3D9_GetDeviceCaps(data->d3d, data->adapter, D3DDEVTYPE_HAL, &caps);
    
    
        device_flags = D3DCREATE_FPU_PRESERVE;
        if (caps.DevCaps & D3DDEVCAPS_HWTRANSFORMANDLIGHT) {
            device_flags |= D3DCREATE_HARDWARE_VERTEXPROCESSING;
        } else {
            device_flags |= D3DCREATE_SOFTWARE_VERTEXPROCESSING;
        }
    
    
        hint = SDL_GetHint(SDL_HINT_RENDER_DIRECT3D_THREADSAFE);
        if (hint && SDL_atoi(hint)) {
            device_flags |= D3DCREATE_MULTITHREADED;
        }
    
    
        result = IDirect3D9_CreateDevice(data->d3d, data->adapter,
                                         D3DDEVTYPE_HAL,
                                         pparams.hDeviceWindow,
                                         device_flags,
                                         &pparams, &data->device);
        if (FAILED(result)) {
            D3D_DestroyRenderer(renderer);
            D3D_SetError("CreateDevice()", result);
            return NULL;
        }
    
    
        /* Get presentation parameters to fill info */
        result = IDirect3DDevice9_GetSwapChain(data->device, 0, &chain);
        if (FAILED(result)) {
            D3D_DestroyRenderer(renderer);
            D3D_SetError("GetSwapChain()", result);
            return NULL;
        }
        result = IDirect3DSwapChain9_GetPresentParameters(chain, &pparams);
        if (FAILED(result)) {
            IDirect3DSwapChain9_Release(chain);
            D3D_DestroyRenderer(renderer);
            D3D_SetError("GetPresentParameters()", result);
            return NULL;
        }
        IDirect3DSwapChain9_Release(chain);
        if (pparams.PresentationInterval == D3DPRESENT_INTERVAL_ONE) {
            renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
        }
        data->pparams = pparams;
    
    
        IDirect3DDevice9_GetDeviceCaps(data->device, &caps);
        renderer->info.max_texture_width = caps.MaxTextureWidth;
        renderer->info.max_texture_height = caps.MaxTextureHeight;
        if (caps.NumSimultaneousRTs >= 2) {
            renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
        }
    
    
        if (caps.PrimitiveMiscCaps & D3DPMISCCAPS_SEPARATEALPHABLEND) {
            data->enableSeparateAlphaBlend = SDL_TRUE;
        }
    
    
        /* Store the default render target */
        IDirect3DDevice9_GetRenderTarget(data->device, 0, &data->defaultRenderTarget );
        data->currentRenderTarget = NULL;
    
    
        /* Set up parameters for rendering */
        D3D_InitRenderState(data);
    
    
        if (caps.MaxSimultaneousTextures >= 3)
        {
    #ifdef ASSEMBLE_SHADER
            /* This shader was created by running the following HLSL through the fxc compiler
               and then tuning the generated assembly.
    
    
               fxc /T fx_4_0 /O3 /Gfa /Fc yuv.fxc yuv.fx
    
    
               --- yuv.fx ---
               Texture2D g_txY;
               Texture2D g_txU;
               Texture2D g_txV;
    
    
               SamplerState samLinear
               {
                   Filter = ANISOTROPIC;
                   AddressU = Clamp;
                   AddressV = Clamp;
                   MaxAnisotropy = 1;
               };
    
    
               struct VS_OUTPUT
               {
                    float2 TextureUV  : TEXCOORD0;
               };
    
    
               struct PS_OUTPUT
               {
                    float4 RGBAColor : SV_Target;
               };
    
    
               PS_OUTPUT YUV420( VS_OUTPUT In ) 
               {
                   const float3 offset = {-0.0625, -0.5, -0.5};
                   const float3 Rcoeff = {1.164,  0.000,  1.596};
                   const float3 Gcoeff = {1.164, -0.391, -0.813};
                   const float3 Bcoeff = {1.164,  2.018,  0.000};
    
    
                   PS_OUTPUT Output;
                   float2 TextureUV = In.TextureUV;
    
    
                   float3 yuv;
                   yuv.x = g_txY.Sample( samLinear, TextureUV ).r;
                   yuv.y = g_txU.Sample( samLinear, TextureUV ).r;
                   yuv.z = g_txV.Sample( samLinear, TextureUV ).r;
    
    
                   yuv += offset;
                   Output.RGBAColor.r = dot(yuv, Rcoeff);
                   Output.RGBAColor.g = dot(yuv, Gcoeff);
                   Output.RGBAColor.b = dot(yuv, Bcoeff);
                   Output.RGBAColor.a = 1.0f;
    
    
                   return Output;
               }
    
    
               technique10 RenderYUV420
               {
                   pass P0
                   {
                        SetPixelShader( CompileShader( ps_4_0_level_9_0, YUV420() ) );
                   }
               }
            */
            const char *shader_text =
                "ps_2_0
    "
                "def c0, -0.0625, -0.5, -0.5, 1
    "
                "def c1, 1.16400003, 0, 1.59599996, 0
    "
                "def c2, 1.16400003, -0.391000003, -0.813000023, 0
    "
                "def c3, 1.16400003, 2.01799989, 0, 0
    "
                "dcl t0.xy
    "
                "dcl v0.xyzw
    "
                "dcl_2d s0
    "
                "dcl_2d s1
    "
                "dcl_2d s2
    "
                "texld r0, t0, s0
    "
                "texld r1, t0, s1
    "
                "texld r2, t0, s2
    "
                "mov r0.y, r1.x
    "
                "mov r0.z, r2.x
    "
                "add r0.xyz, r0, c0
    "
                "dp3 r1.x, r0, c1
    "
                "dp3 r1.y, r0, c2
    "
                "dp2add r1.z, r0, c3, c3.z
    "   /* Logically this is "dp3 r1.z, r0, c3" but the optimizer did its magic */
                "mov r1.w, c0.w
    "
                "mul r0, r1, v0
    "              /* Not in the HLSL, multiply by vertex color */
                "mov oC0, r0
    "
            ;
            LPD3DXBUFFER pCode;
            LPD3DXBUFFER pErrorMsgs;
            LPDWORD shader_data = NULL;
            DWORD   shader_size = 0;
            result = D3DXAssembleShader(shader_text, SDL_strlen(shader_text), NULL, NULL, 0, &pCode, &pErrorMsgs);
            if (!FAILED(result)) {
                shader_data = (DWORD*)pCode->lpVtbl->GetBufferPointer(pCode);
                shader_size = pCode->lpVtbl->GetBufferSize(pCode);
                PrintShaderData(shader_data, shader_size);
            } else {
                const char *error = (const char *)pErrorMsgs->lpVtbl->GetBufferPointer(pErrorMsgs);
                SDL_SetError("Couldn't assemble shader: %s", error);
            }
    #else
            const DWORD shader_data[] = {
                0xffff0200, 0x05000051, 0xa00f0000, 0xbd800000, 0xbf000000, 0xbf000000,
                0x3f800000, 0x05000051, 0xa00f0001, 0x3f94fdf4, 0x00000000, 0x3fcc49ba,
                0x00000000, 0x05000051, 0xa00f0002, 0x3f94fdf4, 0xbec83127, 0xbf5020c5,
                0x00000000, 0x05000051, 0xa00f0003, 0x3f94fdf4, 0x400126e9, 0x00000000,
                0x00000000, 0x0200001f, 0x80000000, 0xb0030000, 0x0200001f, 0x80000000,
                0x900f0000, 0x0200001f, 0x90000000, 0xa00f0800, 0x0200001f, 0x90000000,
                0xa00f0801, 0x0200001f, 0x90000000, 0xa00f0802, 0x03000042, 0x800f0000,
                0xb0e40000, 0xa0e40800, 0x03000042, 0x800f0001, 0xb0e40000, 0xa0e40801,
                0x03000042, 0x800f0002, 0xb0e40000, 0xa0e40802, 0x02000001, 0x80020000,
                0x80000001, 0x02000001, 0x80040000, 0x80000002, 0x03000002, 0x80070000,
                0x80e40000, 0xa0e40000, 0x03000008, 0x80010001, 0x80e40000, 0xa0e40001,
                0x03000008, 0x80020001, 0x80e40000, 0xa0e40002, 0x0400005a, 0x80040001,
                0x80e40000, 0xa0e40003, 0xa0aa0003, 0x02000001, 0x80080001, 0xa0ff0000,
                0x03000005, 0x800f0000, 0x80e40001, 0x90e40000, 0x02000001, 0x800f0800,
                0x80e40000, 0x0000ffff
            };
    #endif
            if (shader_data != NULL) {
                result = IDirect3DDevice9_CreatePixelShader(data->device, shader_data, &data->ps_yuv);
                if (!FAILED(result)) {
                    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
                    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
                } else {
                    D3D_SetError("CreatePixelShader()", result);
                }
            }
        }
    
    
        return renderer;
    }

    D3D_CreateRenderer()这个函数的代码非常长。在这里提取它最重点的几个进行简单的分析。


    PS:因为这个函数中包括了大量的Direct3D的API。这方面假设不熟悉的话。能够參考以下两篇文章:

    最简单的视音频播放演示样例3:Direct3D播放YUV,RGB(通过Surface)

    最简单的视音频播放演示样例4:Direct3D播放RGB(通过Texture)

    (1) 为SDL_Renderer分配内存
    这一步比較简单。直接使用SDL_calloc()分配内存就能够了。

    SDL_calloc()实际上就是calloc()。这一点在前面的文章中已经叙述,在这里不再反复。


    (2) 载入Direct3D
    载入Direct3D通过函数D3D_LoadDLL()完毕。

    调用该函数能够得到一个IDirect3D9类型的接口。IDirect3D9接口能够用于完毕D3D兴许的初始化工作。

    D3D_LoadDLL()函数的代码例如以下。

    SDL_bool D3D_LoadDLL( void **pD3DDLL, IDirect3D9 **pDirect3D9Interface )
    {
    	*pD3DDLL = SDL_LoadObject("D3D9.DLL");
    	if (*pD3DDLL) {
    		IDirect3D9 *(WINAPI * D3DCreate) (UINT SDKVersion);
    
    
    		D3DCreate =
    			(IDirect3D9 * (WINAPI *) (UINT)) SDL_LoadFunction(*pD3DDLL,
    			"Direct3DCreate9");
    		if (D3DCreate) {
    			*pDirect3D9Interface = D3DCreate(D3D_SDK_VERSION);
    		}
    		if (!*pDirect3D9Interface) {
    			SDL_UnloadObject(*pD3DDLL);
    			*pD3DDLL = NULL;
    			return SDL_FALSE;
    		}
    
    
    		return SDL_TRUE;
    	} else {
    		*pDirect3D9Interface = NULL;
    		return SDL_FALSE;
    	}
    }

    从代码中能够看出,该函数载入了一个“D3D9.DLL”的Dll。而且调用了当中的Direct3DCreate9()方法。


    (3) 渲染器接口函数赋值

    SDL_Render结构体中有一系列的函数指针,包括了有关渲染器的各种功能。SDL通过调用这些函数指针就能够调用渲染器相应的功能。这是SDL支持多种渲染器的一个重要特点。代码例如以下所看到的。

        renderer->WindowEvent = D3D_WindowEvent;
        renderer->CreateTexture = D3D_CreateTexture;
        renderer->UpdateTexture = D3D_UpdateTexture;
        renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
        renderer->LockTexture = D3D_LockTexture;
        renderer->UnlockTexture = D3D_UnlockTexture;
        renderer->SetRenderTarget = D3D_SetRenderTarget;
        renderer->UpdateViewport = D3D_UpdateViewport;
        renderer->UpdateClipRect = D3D_UpdateClipRect;
        renderer->RenderClear = D3D_RenderClear;
        renderer->RenderDrawPoints = D3D_RenderDrawPoints;
        renderer->RenderDrawLines = D3D_RenderDrawLines;
        renderer->RenderFillRects = D3D_RenderFillRects;
        renderer->RenderCopy = D3D_RenderCopy;
        renderer->RenderCopyEx = D3D_RenderCopyEx;
        renderer->RenderReadPixels = D3D_RenderReadPixels;
        renderer->RenderPresent = D3D_RenderPresent;
        renderer->DestroyTexture = D3D_DestroyTexture;
        renderer->DestroyRenderer = D3D_DestroyRenderer;

    (4) 创建Device

    创建Direct3D的Device通过IDirect3D9_CreateDevice()函数来实现。这一方面的知识不再叙述,能够參考Direct3D创建Device的相关的文章。

    (5) 设置渲染状态

    设置渲染状态在函数D3D_InitRenderState()中完毕。该部分的知识也不再详述,能够參考Direct3D相关的渲染教程。贴出D3D_InitRenderState()的代码。
    static void D3D_InitRenderState(D3D_RenderData *data)
    {
        D3DMATRIX matrix;
    
    
        IDirect3DDevice9 *device = data->device;
    
    
        IDirect3DDevice9_SetVertexShader(device, NULL);
        IDirect3DDevice9_SetFVF(device, D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX1);
        IDirect3DDevice9_SetRenderState(device, D3DRS_ZENABLE, D3DZB_FALSE);
        IDirect3DDevice9_SetRenderState(device, D3DRS_CULLMODE, D3DCULL_NONE);
        IDirect3DDevice9_SetRenderState(device, D3DRS_LIGHTING, FALSE);
    
    
        /* Enable color modulation by diffuse color */
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLOROP,
                                              D3DTOP_MODULATE);
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG1,
                                              D3DTA_TEXTURE);
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG2,
                                              D3DTA_DIFFUSE);
    
    
        /* Enable alpha modulation by diffuse alpha */
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAOP,
                                              D3DTOP_MODULATE);
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG1,
                                              D3DTA_TEXTURE);
        IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG2,
                                              D3DTA_DIFFUSE);
    
    
        /* Enable separate alpha blend function, if possible */
        if (data->enableSeparateAlphaBlend) {
            IDirect3DDevice9_SetRenderState(device, D3DRS_SEPARATEALPHABLENDENABLE, TRUE);
        }
    
    
        /* Disable second texture stage, since we're done */
        IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_COLOROP,
                                              D3DTOP_DISABLE);
        IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_ALPHAOP,
                                              D3DTOP_DISABLE);
    
    
        /* Set an identity world and view matrix */
        matrix.m[0][0] = 1.0f;
        matrix.m[0][1] = 0.0f;
        matrix.m[0][2] = 0.0f;
        matrix.m[0][3] = 0.0f;
        matrix.m[1][0] = 0.0f;
        matrix.m[1][1] = 1.0f;
        matrix.m[1][2] = 0.0f;
        matrix.m[1][3] = 0.0f;
        matrix.m[2][0] = 0.0f;
        matrix.m[2][1] = 0.0f;
        matrix.m[2][2] = 1.0f;
        matrix.m[2][3] = 0.0f;
        matrix.m[3][0] = 0.0f;
        matrix.m[3][1] = 0.0f;
        matrix.m[3][2] = 0.0f;
        matrix.m[3][3] = 1.0f;
        IDirect3DDevice9_SetTransform(device, D3DTS_WORLD, &matrix);
        IDirect3DDevice9_SetTransform(device, D3DTS_VIEW, &matrix);
    
    
        /* Reset our current scale mode */
        SDL_memset(data->scaleMode, 0xFF, sizeof(data->scaleMode));
    
    
        /* Start the render with beginScene */
        data->beginScene = SDL_TRUE;
    }

    (6) 创建Shader

    创建Shader通过函数IDirect3DDevice9_CreatePixelShader()完毕。

    完毕以上步骤之后,Direct3D的渲染器就创建完毕了。


    2. OpenGL

    OpenGL 的渲染器在创建函数是GL_CreateRenderer()。该函数位于renderopenglSDL_render_gl.c文件里。首先看一下它的代码。

    PS:当中用到了OpenGL的非常多API。假设对OpenGL的API还不熟悉的话,能够參考文章:

    最简单的视音频播放演示样例6:OpenGL播放YUV420P(通过Texture,使用Shader)

    SDL_Renderer * GL_CreateRenderer(SDL_Window * window, Uint32 flags)
    {
        SDL_Renderer *renderer;
        GL_RenderData *data;
        const char *hint;
        GLint value;
        Uint32 window_flags;
        int profile_mask, major, minor;
    
    
        SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile_mask);
        SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major);
        SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor);
        
        window_flags = SDL_GetWindowFlags(window);
        if (!(window_flags & SDL_WINDOW_OPENGL) ||
            profile_mask == SDL_GL_CONTEXT_PROFILE_ES || major != RENDERER_CONTEXT_MAJOR || minor != RENDERER_CONTEXT_MINOR) {
            
            SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 0);
            SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
            SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);
    
    
            if (SDL_RecreateWindow(window, window_flags | SDL_WINDOW_OPENGL) < 0) {
                /* Uh oh, better try to put it back... */
                SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, profile_mask);
                SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, major);
                SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, minor);
                SDL_RecreateWindow(window, window_flags);
                return NULL;
            }
        }
    
    
        renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
        if (!renderer) {
            SDL_OutOfMemory();
            return NULL;
        }
    
    
        data = (GL_RenderData *) SDL_calloc(1, sizeof(*data));
        if (!data) {
            GL_DestroyRenderer(renderer);
            SDL_OutOfMemory();
            return NULL;
        }
    
    
        renderer->WindowEvent = GL_WindowEvent;
        renderer->GetOutputSize = GL_GetOutputSize;
        renderer->CreateTexture = GL_CreateTexture;
        renderer->UpdateTexture = GL_UpdateTexture;
        renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
        renderer->LockTexture = GL_LockTexture;
        renderer->UnlockTexture = GL_UnlockTexture;
        renderer->SetRenderTarget = GL_SetRenderTarget;
        renderer->UpdateViewport = GL_UpdateViewport;
        renderer->UpdateClipRect = GL_UpdateClipRect;
        renderer->RenderClear = GL_RenderClear;
        renderer->RenderDrawPoints = GL_RenderDrawPoints;
        renderer->RenderDrawLines = GL_RenderDrawLines;
        renderer->RenderFillRects = GL_RenderFillRects;
        renderer->RenderCopy = GL_RenderCopy;
        renderer->RenderCopyEx = GL_RenderCopyEx;
        renderer->RenderReadPixels = GL_RenderReadPixels;
        renderer->RenderPresent = GL_RenderPresent;
        renderer->DestroyTexture = GL_DestroyTexture;
        renderer->DestroyRenderer = GL_DestroyRenderer;
        renderer->GL_BindTexture = GL_BindTexture;
        renderer->GL_UnbindTexture = GL_UnbindTexture;
        renderer->info = GL_RenderDriver.info;
        renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
        renderer->driverdata = data;
        renderer->window = window;
    
    
        data->context = SDL_GL_CreateContext(window);
        if (!data->context) {
            GL_DestroyRenderer(renderer);
            return NULL;
        }
        if (SDL_GL_MakeCurrent(window, data->context) < 0) {
            GL_DestroyRenderer(renderer);
            return NULL;
        }
    
    
        if (GL_LoadFunctions(data) < 0) {
            GL_DestroyRenderer(renderer);
            return NULL;
        }
    
    
    #ifdef __MACOSX__
        /* Enable multi-threaded rendering */
        /* Disabled until Ryan finishes his VBO/PBO code...
           CGLEnable(CGLGetCurrentContext(), kCGLCEMPEngine);
         */
    #endif
    
    
        if (flags & SDL_RENDERER_PRESENTVSYNC) {
            SDL_GL_SetSwapInterval(1);
        } else {
            SDL_GL_SetSwapInterval(0);
        }
        if (SDL_GL_GetSwapInterval() > 0) {
            renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
        }
    
    
        /* Check for debug output support */
        if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_FLAGS, &value) == 0 &&
            (value & SDL_GL_CONTEXT_DEBUG_FLAG)) {
            data->debug_enabled = SDL_TRUE;
        }
        if (data->debug_enabled && SDL_GL_ExtensionSupported("GL_ARB_debug_output")) {
            PFNGLDEBUGMESSAGECALLBACKARBPROC glDebugMessageCallbackARBFunc = (PFNGLDEBUGMESSAGECALLBACKARBPROC) SDL_GL_GetProcAddress("glDebugMessageCallbackARB");
    
    
            data->GL_ARB_debug_output_supported = SDL_TRUE;
            data->glGetPointerv(GL_DEBUG_CALLBACK_FUNCTION_ARB, (GLvoid **)&data->next_error_callback);
            data->glGetPointerv(GL_DEBUG_CALLBACK_USER_PARAM_ARB, &data->next_error_userparam);
            glDebugMessageCallbackARBFunc(GL_HandleDebugMessage, renderer);
    
    
            /* Make sure our callback is called when errors actually happen */
            data->glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
        }
    
    
        if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
            || SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
            data->GL_ARB_texture_rectangle_supported = SDL_TRUE;
            data->glGetIntegerv(GL_MAX_RECTANGLE_TEXTURE_SIZE_ARB, &value);
            renderer->info.max_texture_width = value;
            renderer->info.max_texture_height = value;
        } else {
            data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
            renderer->info.max_texture_width = value;
            renderer->info.max_texture_height = value;
        }
    
    
        /* Check for multitexture support */
        if (SDL_GL_ExtensionSupported("GL_ARB_multitexture")) {
            data->glActiveTextureARB = (PFNGLACTIVETEXTUREARBPROC) SDL_GL_GetProcAddress("glActiveTextureARB");
            if (data->glActiveTextureARB) {
                data->GL_ARB_multitexture_supported = SDL_TRUE;
                data->glGetIntegerv(GL_MAX_TEXTURE_UNITS_ARB, &data->num_texture_units);
            }
        }
    
    
        /* Check for shader support */
        hint = SDL_GetHint(SDL_HINT_RENDER_OPENGL_SHADERS);
        if (!hint || *hint != '0') {
            data->shaders = GL_CreateShaderContext();
        }
        SDL_LogInfo(SDL_LOG_CATEGORY_RENDER, "OpenGL shaders: %s",
                    data->shaders ? "ENABLED" : "DISABLED");
    
    
        /* We support YV12 textures using 3 textures and a shader */
        if (data->shaders && data->num_texture_units >= 3) {
            renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
            renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
        }
    
    
    #ifdef __MACOSX__
        renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_UYVY;
    #endif
    
    
        if (SDL_GL_ExtensionSupported("GL_EXT_framebuffer_object")) {
            data->GL_EXT_framebuffer_object_supported = SDL_TRUE;
            data->glGenFramebuffersEXT = (PFNGLGENFRAMEBUFFERSEXTPROC)
                SDL_GL_GetProcAddress("glGenFramebuffersEXT");
            data->glDeleteFramebuffersEXT = (PFNGLDELETEFRAMEBUFFERSEXTPROC)
                SDL_GL_GetProcAddress("glDeleteFramebuffersEXT");
            data->glFramebufferTexture2DEXT = (PFNGLFRAMEBUFFERTEXTURE2DEXTPROC)
                SDL_GL_GetProcAddress("glFramebufferTexture2DEXT");
            data->glBindFramebufferEXT = (PFNGLBINDFRAMEBUFFEREXTPROC)
                SDL_GL_GetProcAddress("glBindFramebufferEXT");
            data->glCheckFramebufferStatusEXT = (PFNGLCHECKFRAMEBUFFERSTATUSEXTPROC)
                SDL_GL_GetProcAddress("glCheckFramebufferStatusEXT");
            renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
        }
        data->framebuffers = NULL;
    
    
        /* Set up parameters for rendering */
        GL_ResetState(renderer);
    
    
        return renderer;
    }

    GL_CreateRenderer()这个函数的代码非常长。

    在这里提取它最重点的几个进行简单的分析。



    (1) 为SDL_Renderer分配内存

    这一步比較简单。

    直接使用SDL_calloc()分配内存就能够了。

    (2) 渲染器接口函数赋值

    SDL_Render结构体中有一系列的函数指针,包括了有关渲染器的各种功能。这一点在Direct3D的时候已经提过。不再反复。

    代码例如以下。

        renderer->WindowEvent = GL_WindowEvent;
        renderer->GetOutputSize = GL_GetOutputSize;
        renderer->CreateTexture = GL_CreateTexture;
        renderer->UpdateTexture = GL_UpdateTexture;
        renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
        renderer->LockTexture = GL_LockTexture;
        renderer->UnlockTexture = GL_UnlockTexture;
        renderer->SetRenderTarget = GL_SetRenderTarget;
        renderer->UpdateViewport = GL_UpdateViewport;
        renderer->UpdateClipRect = GL_UpdateClipRect;
        renderer->RenderClear = GL_RenderClear;
        renderer->RenderDrawPoints = GL_RenderDrawPoints;
        renderer->RenderDrawLines = GL_RenderDrawLines;
        renderer->RenderFillRects = GL_RenderFillRects;
        renderer->RenderCopy = GL_RenderCopy;
        renderer->RenderCopyEx = GL_RenderCopyEx;
        renderer->RenderReadPixels = GL_RenderReadPixels;
        renderer->RenderPresent = GL_RenderPresent;
        renderer->DestroyTexture = GL_DestroyTexture;
        renderer->DestroyRenderer = GL_DestroyRenderer;
        renderer->GL_BindTexture = GL_BindTexture;
        renderer->GL_UnbindTexture = GL_UnbindTexture;

    (3) 初始化OpenGL
    初始化OpenGL各种变量,包括SDL_GL_CreateContext(),SDL_GL_MakeCurrent(),GL_LoadFunctions()等函数。这一部分还没有具体分析。

    (4) 初始化Shader

    对Shader的初始化在函数GL_CreateShaderContext()中完毕。

    GL_CreateShaderContext()的代码例如以下(位于renderopenglSDL_shaders_gl.c)。

    GL_ShaderContext * GL_CreateShaderContext()
    {
        GL_ShaderContext *ctx;
        SDL_bool shaders_supported;
        int i;
    
    
        ctx = (GL_ShaderContext *)SDL_calloc(1, sizeof(*ctx));
        if (!ctx) {
            return NULL;
        }
    
    
        if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
            || SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
            ctx->GL_ARB_texture_rectangle_supported = SDL_TRUE;
        }
    
    
        /* Check for shader support */
        shaders_supported = SDL_FALSE;
        if (SDL_GL_ExtensionSupported("GL_ARB_shader_objects") &&
            SDL_GL_ExtensionSupported("GL_ARB_shading_language_100") &&
            SDL_GL_ExtensionSupported("GL_ARB_vertex_shader") &&
            SDL_GL_ExtensionSupported("GL_ARB_fragment_shader")) {
            ctx->glGetError = (GLenum (*)(void)) SDL_GL_GetProcAddress("glGetError");
            ctx->glAttachObjectARB = (PFNGLATTACHOBJECTARBPROC) SDL_GL_GetProcAddress("glAttachObjectARB");
            ctx->glCompileShaderARB = (PFNGLCOMPILESHADERARBPROC) SDL_GL_GetProcAddress("glCompileShaderARB");
            ctx->glCreateProgramObjectARB = (PFNGLCREATEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glCreateProgramObjectARB");
            ctx->glCreateShaderObjectARB = (PFNGLCREATESHADEROBJECTARBPROC) SDL_GL_GetProcAddress("glCreateShaderObjectARB");
            ctx->glDeleteObjectARB = (PFNGLDELETEOBJECTARBPROC) SDL_GL_GetProcAddress("glDeleteObjectARB");
            ctx->glGetInfoLogARB = (PFNGLGETINFOLOGARBPROC) SDL_GL_GetProcAddress("glGetInfoLogARB");
            ctx->glGetObjectParameterivARB = (PFNGLGETOBJECTPARAMETERIVARBPROC) SDL_GL_GetProcAddress("glGetObjectParameterivARB");
            ctx->glGetUniformLocationARB = (PFNGLGETUNIFORMLOCATIONARBPROC) SDL_GL_GetProcAddress("glGetUniformLocationARB");
            ctx->glLinkProgramARB = (PFNGLLINKPROGRAMARBPROC) SDL_GL_GetProcAddress("glLinkProgramARB");
            ctx->glShaderSourceARB = (PFNGLSHADERSOURCEARBPROC) SDL_GL_GetProcAddress("glShaderSourceARB");
            ctx->glUniform1iARB = (PFNGLUNIFORM1IARBPROC) SDL_GL_GetProcAddress("glUniform1iARB");
            ctx->glUniform1fARB = (PFNGLUNIFORM1FARBPROC) SDL_GL_GetProcAddress("glUniform1fARB");
            ctx->glUseProgramObjectARB = (PFNGLUSEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glUseProgramObjectARB");
            if (ctx->glGetError &&
                ctx->glAttachObjectARB &&
                ctx->glCompileShaderARB &&
                ctx->glCreateProgramObjectARB &&
                ctx->glCreateShaderObjectARB &&
                ctx->glDeleteObjectARB &&
                ctx->glGetInfoLogARB &&
                ctx->glGetObjectParameterivARB &&
                ctx->glGetUniformLocationARB &&
                ctx->glLinkProgramARB &&
                ctx->glShaderSourceARB &&
                ctx->glUniform1iARB &&
                ctx->glUniform1fARB &&
                ctx->glUseProgramObjectARB) {
                shaders_supported = SDL_TRUE;
            }
        }
    
    
        if (!shaders_supported) {
            SDL_free(ctx);
            return NULL;
        }
    
    
        /* Compile all the shaders */
        for (i = 0; i < NUM_SHADERS; ++i) {
            if (!CompileShaderProgram(ctx, i, &ctx->shaders[i])) {
                GL_DestroyShaderContext(ctx);
                return NULL;
            }
        }
    
    
        /* We're done! */
        return ctx;
    }

    上述代码主要完毕了以下两步:
    第一步,初始化GL_ShaderContext。GL_ShaderContext中包括了OpenGL的Shader方面用到的各种接口函数。GL_ShaderContext定义例如以下。
    struct GL_ShaderContext
    {
        GLenum (*glGetError)(void);
    
    
        PFNGLATTACHOBJECTARBPROC glAttachObjectARB;
        PFNGLCOMPILESHADERARBPROC glCompileShaderARB;
        PFNGLCREATEPROGRAMOBJECTARBPROC glCreateProgramObjectARB;
        PFNGLCREATESHADEROBJECTARBPROC glCreateShaderObjectARB;
        PFNGLDELETEOBJECTARBPROC glDeleteObjectARB;
        PFNGLGETINFOLOGARBPROC glGetInfoLogARB;
        PFNGLGETOBJECTPARAMETERIVARBPROC glGetObjectParameterivARB;
        PFNGLGETUNIFORMLOCATIONARBPROC glGetUniformLocationARB;
        PFNGLLINKPROGRAMARBPROC glLinkProgramARB;
        PFNGLSHADERSOURCEARBPROC glShaderSourceARB;
        PFNGLUNIFORM1IARBPROC glUniform1iARB;
        PFNGLUNIFORM1FARBPROC glUniform1fARB;
        PFNGLUSEPROGRAMOBJECTARBPROC glUseProgramObjectARB;
    
    
        SDL_bool GL_ARB_texture_rectangle_supported;
    
    
        GL_ShaderData shaders[NUM_SHADERS];
    };

    看这个结构体的定义会给人一种非常混乱的感觉。

    不用去理会那些大串的大写字母,仅仅要知道这个结构体是函数的接口的“合集”就能够了。

    从函数的名称中我们能够看出有编译Shader的glCreateShaderObject(),glShaderSource(),glCompileShader()等;以及编译Program的glCreateProgramObject()。glAttachObject (),glLinkProgram(),glUseProgramObject ()等等。
    GL_CreateShaderContext()函数中创建了一个GL_ShaderContext并对当中的接口函数进行了赋值。

    第二步,编译Shader程序。该功能在CompileShaderProgram()函数中完毕。

    CompileShaderProgram()的函数代码例如以下所看到的。

    static SDL_bool CompileShaderProgram(GL_ShaderContext *ctx, int index, GL_ShaderData *data)
    {
        const int num_tmus_bound = 4;
        const char *vert_defines = "";
        const char *frag_defines = "";
        int i;
        GLint location;
    
    
        if (index == SHADER_NONE) {
            return SDL_TRUE;
        }
    
    
        ctx->glGetError();
    
    
        /* Make sure we use the correct sampler type for our texture type */
        if (ctx->GL_ARB_texture_rectangle_supported) {
            frag_defines =
    "#define sampler2D sampler2DRect
    "
    "#define texture2D texture2DRect
    ";
        }
    
    
        /* Create one program object to rule them all */
        data->program = ctx->glCreateProgramObjectARB();
    
    
        /* Create the vertex shader */
        data->vert_shader = ctx->glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);
        if (!CompileShader(ctx, data->vert_shader, vert_defines, shader_source[index][0])) {
            return SDL_FALSE;
        }
    
    
        /* Create the fragment shader */
        data->frag_shader = ctx->glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
        if (!CompileShader(ctx, data->frag_shader, frag_defines, shader_source[index][1])) {
            return SDL_FALSE;
        }
    
    
        /* ... and in the darkness bind them */
        ctx->glAttachObjectARB(data->program, data->vert_shader);
        ctx->glAttachObjectARB(data->program, data->frag_shader);
        ctx->glLinkProgramARB(data->program);
    
    
        /* Set up some uniform variables */
        ctx->glUseProgramObjectARB(data->program);
        for (i = 0; i < num_tmus_bound; ++i) {
            char tex_name[10];
            SDL_snprintf(tex_name, SDL_arraysize(tex_name), "tex%d", i);
            location = ctx->glGetUniformLocationARB(data->program, tex_name);
            if (location >= 0) {
                ctx->glUniform1iARB(location, i);
            }
        }
        ctx->glUseProgramObjectARB(0);
    
    
        return (ctx->glGetError() == GL_NO_ERROR);
    }

    从代码中能够看出。这个函数调用了GL_ShaderContext中用于初始化Shader以及Program的各个函数。有关初始化的流程不再细说,能够參考相关的文章。

    在该函数中,调用了CompileShader()专门用于初始化Shader。

    该函数被调用了两次,分别用于初始化vertex shader和fragment shader。

    CompileShader()的代码例如以下。

    static SDL_bool CompileShader(GL_ShaderContext *ctx, GLhandleARB shader, const char *defines, const char *source)
    {
        GLint status;
        const char *sources[2];
    
    
        sources[0] = defines;
        sources[1] = source;
    
    
        ctx->glShaderSourceARB(shader, SDL_arraysize(sources), sources, NULL);
        ctx->glCompileShaderARB(shader);
        ctx->glGetObjectParameterivARB(shader, GL_OBJECT_COMPILE_STATUS_ARB, &status);
        if (status == 0) {
            GLint length;
            char *info;
    
    
            ctx->glGetObjectParameterivARB(shader, GL_OBJECT_INFO_LOG_LENGTH_ARB, &length);
            info = SDL_stack_alloc(char, length+1);
            ctx->glGetInfoLogARB(shader, length, NULL, info);
            SDL_LogError(SDL_LOG_CATEGORY_RENDER,
                "Failed to compile shader:
    %s%s
    %s", defines, source, info);
    #ifdef DEBUG_SHADERS
            fprintf(stderr,
                "Failed to compile shader:
    %s%s
    %s", defines, source, info);
    #endif
            SDL_stack_free(info);
    
    
            return SDL_FALSE;
        } else {
            return SDL_TRUE;
        }
    }

    从代码中能够看出,该函数调用glShaderSource()。glCompileShader()。glGetObjectParameteriv()这几个函数初始化一个Shader。
    Shader的代码位于一个名称为shader_source的char型二维数组里。源码例如以下所看到的。

    数组中每一个元素代表一个Shader的代码,每一个Shader的代码包括两个部分:vertex shader代码(相应元素[0])以及fragment shader代码(相应元素[1])。


    /*
     * NOTE: Always use sampler2D, etc here. We'll #define them to the
     *  texture_rectangle versions if we choose to use that extension.
     */
    static const char *shader_source[NUM_SHADERS][2] =
    {
        /* SHADER_NONE */
        { NULL, NULL },
    
    
        /* SHADER_SOLID */
        {
            /* vertex shader */
    "varying vec4 v_color;
    "
    "
    "
    "void main()
    "
    "{
    "
    "    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
    "
    "    v_color = gl_Color;
    "
    "}",
            /* fragment shader */
    "varying vec4 v_color;
    "
    "
    "
    "void main()
    "
    "{
    "
    "    gl_FragColor = v_color;
    "
    "}"
        },
    
    
        /* SHADER_RGB */
        {
            /* vertex shader */
    "varying vec4 v_color;
    "
    "varying vec2 v_texCoord;
    "
    "
    "
    "void main()
    "
    "{
    "
    "    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
    "
    "    v_color = gl_Color;
    "
    "    v_texCoord = vec2(gl_MultiTexCoord0);
    "
    "}",
            /* fragment shader */
    "varying vec4 v_color;
    "
    "varying vec2 v_texCoord;
    "
    "uniform sampler2D tex0;
    "
    "
    "
    "void main()
    "
    "{
    "
    "    gl_FragColor = texture2D(tex0, v_texCoord) * v_color;
    "
    "}"
        },
    
    
        /* SHADER_YV12 */
        {
            /* vertex shader */
    "varying vec4 v_color;
    "
    "varying vec2 v_texCoord;
    "
    "
    "
    "void main()
    "
    "{
    "
    "    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
    "
    "    v_color = gl_Color;
    "
    "    v_texCoord = vec2(gl_MultiTexCoord0);
    "
    "}",
            /* fragment shader */
    "varying vec4 v_color;
    "
    "varying vec2 v_texCoord;
    "
    "uniform sampler2D tex0; // Y 
    "
    "uniform sampler2D tex1; // U 
    "
    "uniform sampler2D tex2; // V 
    "
    "
    "
    "// YUV offset 
    "
    "const vec3 offset = vec3(-0.0625, -0.5, -0.5);
    "
    "
    "
    "// RGB coefficients 
    "
    "const vec3 Rcoeff = vec3(1.164,  0.000,  1.596);
    "
    "const vec3 Gcoeff = vec3(1.164, -0.391, -0.813);
    "
    "const vec3 Bcoeff = vec3(1.164,  2.018,  0.000);
    "
    "
    "
    "void main()
    "
    "{
    "
    "    vec2 tcoord;
    "
    "    vec3 yuv, rgb;
    "
    "
    "
    "    // Get the Y value 
    "
    "    tcoord = v_texCoord;
    "
    "    yuv.x = texture2D(tex0, tcoord).r;
    "
    "
    "
    "    // Get the U and V values 
    "
    "    tcoord *= 0.5;
    "
    "    yuv.y = texture2D(tex1, tcoord).r;
    "
    "    yuv.z = texture2D(tex2, tcoord).r;
    "
    "
    "
    "    // Do the color transform 
    "
    "    yuv += offset;
    "
    "    rgb.r = dot(yuv, Rcoeff);
    "
    "    rgb.g = dot(yuv, Gcoeff);
    "
    "    rgb.b = dot(yuv, Bcoeff);
    "
    "
    "
    "    // That was easy. :) 
    "
    "    gl_FragColor = vec4(rgb, 1.0) * v_color;
    "
    "}"
        },
    };

    有关OpenGL的渲染器的初始化代码临时分析到这里。

    3. Software

    Software的渲染器在创建函数是SW_CreateRenderer()。该函数位于rendersoftwareSDL_render_sw.c文件里。首先看一下它的代码。

    SDL_Renderer * SW_CreateRenderer(SDL_Window * window, Uint32 flags)
    {
        SDL_Surface *surface;
    
    
        surface = SDL_GetWindowSurface(window);
        if (!surface) {
            return NULL;
        }
        return SW_CreateRendererForSurface(surface);
    }

    从代码中能够看出,SW_CreateRenderer()调用了2个函数:SDL_GetWindowSurface()和SW_CreateRendererForSurface()。SDL_GetWindowSurface()用于创建一个Surface;SW_CreateRendererForSurface()基于Surface创建一个Renderer。
    以下分别看一下这2个函数的代码。
    SDL_GetWindowSurface()的代码例如以下所看到的(位于videoSDL_video.c)。
    SDL_Surface * SDL_GetWindowSurface(SDL_Window * window)
    {
        CHECK_WINDOW_MAGIC(window, NULL);
    
    
        if (!window->surface_valid) {
            if (window->surface) {
                window->surface->flags &= ~SDL_DONTFREE;
                SDL_FreeSurface(window->surface);
            }
            window->surface = SDL_CreateWindowFramebuffer(window);
            if (window->surface) {
                window->surface_valid = SDL_TRUE;
                window->surface->flags |= SDL_DONTFREE;
            }
        }
        return window->surface;
    }

    当中调用了一个函数SDL_CreateWindowFramebuffer()。看一下该函数的代码。
    static SDL_Surface * SDL_CreateWindowFramebuffer(SDL_Window * window)
    {
        Uint32 format;
        void *pixels;
        int pitch;
        int bpp;
        Uint32 Rmask, Gmask, Bmask, Amask;
    
    
        if (!_this->CreateWindowFramebuffer || !_this->UpdateWindowFramebuffer) {
            return NULL;
        }
    
    
        if (_this->CreateWindowFramebuffer(_this, window, &format, &pixels, &pitch) < 0) {
            return NULL;
        }
    
    
        if (!SDL_PixelFormatEnumToMasks(format, &bpp, &Rmask, &Gmask, &Bmask, &Amask)) {
            return NULL;
        }
    
    
        return SDL_CreateRGBSurfaceFrom(pixels, window->w, window->h, bpp, pitch, Rmask, Gmask, Bmask, Amask);
    }

    该函数中调用了SDL_VideoDevice中的一个函数CreateWindowFramebuffer()。

    我们以“Windows视频驱动”为例,看看CreateWindowFramebuffer()中的代码。在“Windows视频驱动”下,CreateWindowFramebuffer()相应的函数是WIN_CreateWindowFramebuffer()。

    以下看一下该函数的代码。

    int WIN_CreateWindowFramebuffer(_THIS, SDL_Window * window, Uint32 * format, void ** pixels, int *pitch)
    {
        SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
        size_t size;
        LPBITMAPINFO info;
        HBITMAP hbm;
    
    
        /* Free the old framebuffer surface */
        if (data->mdc) {
            DeleteDC(data->mdc);
        }
        if (data->hbm) {
            DeleteObject(data->hbm);
        }
    
    
        /* Find out the format of the screen */
        size = sizeof(BITMAPINFOHEADER) + 256 * sizeof (RGBQUAD);
        info = (LPBITMAPINFO)SDL_stack_alloc(Uint8, size);
    
    
        SDL_memset(info, 0, size);
        info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    
    
        /* The second call to GetDIBits() fills in the bitfields */
        hbm = CreateCompatibleBitmap(data->hdc, 1, 1);
        GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
        GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
        DeleteObject(hbm);
    
    
        *format = SDL_PIXELFORMAT_UNKNOWN;
        if (info->bmiHeader.biCompression == BI_BITFIELDS) {
            int bpp;
            Uint32 *masks;
    
    
            bpp = info->bmiHeader.biPlanes * info->bmiHeader.biBitCount;
            masks = (Uint32*)((Uint8*)info + info->bmiHeader.biSize);
            *format = SDL_MasksToPixelFormatEnum(bpp, masks[0], masks[1], masks[2], 0);
        }
        if (*format == SDL_PIXELFORMAT_UNKNOWN)
        {
            /* We'll use RGB format for now */
            *format = SDL_PIXELFORMAT_RGB888;
    
    
            /* Create a new one */
            SDL_memset(info, 0, size);
            info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
            info->bmiHeader.biPlanes = 1;
            info->bmiHeader.biBitCount = 32;
            info->bmiHeader.biCompression = BI_RGB;
        }
    
    
        /* Fill in the size information */
        *pitch = (((window->w * SDL_BYTESPERPIXEL(*format)) + 3) & ~3);
        info->bmiHeader.biWidth = window->w;
        info->bmiHeader.biHeight = -window->h;  /* negative for topdown bitmap */
        info->bmiHeader.biSizeImage = window->h * (*pitch);
    
    
        data->mdc = CreateCompatibleDC(data->hdc);
        data->hbm = CreateDIBSection(data->hdc, info, DIB_RGB_COLORS, pixels, NULL, 0);
        SDL_stack_free(info);
    
    
        if (!data->hbm) {
            return WIN_SetError("Unable to create DIB");
        }
        SelectObject(data->mdc, data->hbm);
    
    
        return 0;
    }

    从代码中能够看出,该函数调用了Win32的API函数CreateCompatibleBitmap(),CreateCompatibleDC()等一系列方法创建了“Surface”。



    SDL_GetWindowSurface()函数到此分析完毕,如今回过头来再看SW_CreateRenderer ()的还有一个函数SW_CreateRendererForSurface()。

    该函数的代码例如以下。


    SDL_Renderer * SW_CreateRendererForSurface(SDL_Surface * surface)
    {
        SDL_Renderer *renderer;
        SW_RenderData *data;
    
    
        if (!surface) {
            SDL_SetError("Can't create renderer for NULL surface");
            return NULL;
        }
    
    
        renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
        if (!renderer) {
            SDL_OutOfMemory();
            return NULL;
        }
    
    
        data = (SW_RenderData *) SDL_calloc(1, sizeof(*data));
        if (!data) {
            SW_DestroyRenderer(renderer);
            SDL_OutOfMemory();
            return NULL;
        }
        data->surface = surface;
    
    
        renderer->WindowEvent = SW_WindowEvent;
        renderer->GetOutputSize = SW_GetOutputSize;
        renderer->CreateTexture = SW_CreateTexture;
        renderer->SetTextureColorMod = SW_SetTextureColorMod;
        renderer->SetTextureAlphaMod = SW_SetTextureAlphaMod;
        renderer->SetTextureBlendMode = SW_SetTextureBlendMode;
        renderer->UpdateTexture = SW_UpdateTexture;
        renderer->LockTexture = SW_LockTexture;
        renderer->UnlockTexture = SW_UnlockTexture;
        renderer->SetRenderTarget = SW_SetRenderTarget;
        renderer->UpdateViewport = SW_UpdateViewport;
        renderer->UpdateClipRect = SW_UpdateClipRect;
        renderer->RenderClear = SW_RenderClear;
        renderer->RenderDrawPoints = SW_RenderDrawPoints;
        renderer->RenderDrawLines = SW_RenderDrawLines;
        renderer->RenderFillRects = SW_RenderFillRects;
        renderer->RenderCopy = SW_RenderCopy;
        renderer->RenderCopyEx = SW_RenderCopyEx;
        renderer->RenderReadPixels = SW_RenderReadPixels;
        renderer->RenderPresent = SW_RenderPresent;
        renderer->DestroyTexture = SW_DestroyTexture;
        renderer->DestroyRenderer = SW_DestroyRenderer;
        renderer->info = SW_RenderDriver.info;
        renderer->driverdata = data;
    
    
        SW_ActivateRenderer(renderer);
    
    
        return renderer;
    }

    与前面的函数一样,该函数完毕了SDL_Renderer结构体中函数指针的赋值。




    版权声明:本文博主原创文章,博客,未经同意不得转载。

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  • 原文地址:https://www.cnblogs.com/yxwkf/p/4808143.html
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