在上一篇文章我们知道了如何在android使用SDL2.0来渲染显示一张bmp图，但是如果是一张png或者一张jpg的图，那么还能显示成功么？答案是否定的
我们需要移植SDL_image库来支持除bmp之外的图片格式。
一、移植SDL_image库：
使用如下命令，从SDL Mercurial获取SDL_image的源码：
hg clone https://hg.libsdl.org/SDL_image/
将SDL_image拷贝到在上一篇文章中的android-projectjni下，将平台相关的代码去掉以及自动自动化相关的文件去掉，保留android相关的代码与文件。
二、在android添加相关的引用：
修改android-projectjnisrcAndroid.mk，添加相关的引用:
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := main SDL_PATH := ../SDL SDL_IMAGE_PATH := ../SDL2_image LOCAL_C_INCLUDES := $(LOCAL_PATH)/$(SDL_PATH)/include $(LOCAL_PATH)/$(SDL_IMAGE_PATH) # Add your application source files here... LOCAL_SRC_FILES := $(SDL_PATH)/src/main/android/SDL_android_main.c SDL_lesson.c LOCAL_SHARED_LIBRARIES := SDL2 LOCAL_SHARED_LIBRARIES += SDL2_image LOCAL_LDLIBS := -lGLESv1_CM -lGLESv2 -llog include $(BUILD_SHARED_LIBRARY)
三、代码中引用相关的头文件：
/* * SDL_lesson.c * Clipping Sprite Sheets * Created on: Aug 12, 2014 * Author: clarck */ #include <jni.h> #include "SDL.h" #include "SDL_image.h" #include "SDL_logger.h" #include "SDL_main.h" #include "SDL_cleanup.h" //The attributes of the screen const int SCREEN_WIDTH = 640; const int SCREEN_HEIGHT = 480; struct SDL_Window *window = NULL; struct SDL_Renderer *render = NULL; struct SDL_Texture *background = NULL; struct SDL_Texture *image = NULL;
四、加载图片的部分修改为IMG_LoadTexture:
/* * SDL_lesson.c * Clipping Sprite Sheets * Created on: Aug 12, 2014 * Author: clarck */ #include <jni.h> #include "SDL.h" #include "SDL_image.h" #include "SDL_logger.h" #include "SDL_main.h" #include "SDL_cleanup.h" //The attributes of the screen const int SCREEN_WIDTH = 640; const int SCREEN_HEIGHT = 480; struct SDL_Window *window = NULL; struct SDL_Renderer *render = NULL; struct SDL_Texture *background = NULL; struct SDL_Texture *image = NULL; /* * Loads a image into a texture on the rendering device * @param file The image file to load * @param ren The renderer to load the texture onto * @return the loaded texture, or NULL if something went wrong. */ SDL_Texture* loadTexture(const char *file, SDL_Renderer *render) { struct SDL_Texture *texture = NULL; texture = IMG_LoadTexture(render, file); if (texture == NULL) { LOGE("SDL_CreateTextureFromSurface failed %s", SDL_GetError()); } else { LOGI("SDL_CreateTextureFromSurface successful."); } return texture; }
五、编写主函数：
/* * SDL_lesson.c * Clipping Sprite Sheets * Created on: Aug 12, 2014 * Author: clarck */ #include <jni.h> #include "SDL.h" #include "SDL_image.h" #include "SDL_logger.h" #include "SDL_main.h" #include "SDL_cleanup.h" //The attributes of the screen const int SCREEN_WIDTH = 640; const int SCREEN_HEIGHT = 480; struct SDL_Window *window = NULL; struct SDL_Renderer *render = NULL; struct SDL_Texture *background = NULL; struct SDL_Texture *image = NULL; /* * Loads a image into a texture on the rendering device * @param file The image file to load * @param ren The renderer to load the texture onto * @return the loaded texture, or NULL if something went wrong. */ SDL_Texture* loadTexture(const char *file, SDL_Renderer *render) { struct SDL_Texture *texture = NULL; texture = IMG_LoadTexture(render, file); if (texture == NULL) { LOGE("SDL_CreateTextureFromSurface failed %s", SDL_GetError()); } else { LOGI("SDL_CreateTextureFromSurface successful."); } return texture; } /* * Draw an SDL_Texture to an SDL_Renderer at position x, y, preserving * the texture's width and height * @param tex The source texture we want to draw * @param ren The renderer we want to draw too * @param x The x coordinate to draw too * @param y The y coordinate to draw too * @param w The width of the texture to draw * @param h The height of the texture to draw */ void renderTexture(SDL_Texture *tex, SDL_Renderer *ren, SDL_Rect dst, SDL_Rect *clip) { SDL_RenderCopy(ren, tex, clip, &dst); } /* * Draw an SDL_Texture to an SDL_Renderer at position x, y, preserving * the texture's width and height and taking a clip of the texture if desired * If a clip is passed, the clip's width and height will be used instead of the texture's * @param tex The source texture we want to draw * @param rend The renderer we want to draw too * @param x The x coordinate to draw too * @param y The y coordinate to draw too * @param clip The sub-section of the texture to draw (clipping rect) * default of nullptr draws the entire texture */ void renderTexture2(SDL_Texture *tex, SDL_Renderer *ren, int x, int y, SDL_Rect *clip) { SDL_Rect dst; dst.x = x; dst.y = y; if (clip != NULL) { dst.w = clip->w; dst.h = clip->h; } else { SDL_QueryTexture(tex, NULL, NULL, &dst.w, &dst.h); } renderTexture(tex, ren, dst, clip); } int main(int argc, char *argv[]) { //char *filefolder = "/storage/sdcard0/"; char *filefolder = argv[1]; char *image_temp = "image.png"; char *background_temp = "background.png"; LOGI("natvie_SDL %s", filefolder); char *background_file = (char*) malloc( strlen(filefolder) + strlen(background_temp) + 1); strcpy(background_file, filefolder); strcat(background_file, background_temp); char *image_file = (char*) malloc( strlen(filefolder) + strlen(image_temp) + 1); strcpy(image_file, filefolder); strcat(image_file, image_temp); LOGI("natvie_SDL %s", image_file); if (SDL_Init(SDL_INIT_EVERYTHING) != 0) { LOGE("SDL_Init failed %s", SDL_GetError()); } window = SDL_CreateWindow("lesson5", 100, 100, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN); if (window == NULL) { LOGE("SDL_CreateWindow failed %s", SDL_GetError()); } render = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC); if (render == NULL) { LOGE("SDL_CreateRenderer failed %s", SDL_GetError()); } background = loadTexture(background_file, render); image = loadTexture(image_file, render); //Clear the window SDL_RenderClear(render); //Get the width and height from the texture so we know how much to move x,y by //to tile it correctly int bW, bH; SDL_QueryTexture(background, NULL, NULL, &bW, &bH); //Draw our image in the center of the window //We need the foreground image's width to properly compute the position //of it's top left corner so that the image will be centered int iW = 100, iH = 100; int x = SCREEN_WIDTH / 2 - iW / 2; int y = SCREEN_HEIGHT / 2 - iH / 2; //Setup the clips for our image SDL_Rect clips[4]; int i; for (i = 0; i < 4; i++) { clips[i].x = i / 2 * iW; clips[i].y = i % 2 * iH; clips[i].w = iW; clips[i].h = iH; } //Specify a default clip to start with int useClip = 0; SDL_Event e; int quit = 1; while (quit != 0) { //Read any events that occured, for now we'll just quit if any event occurs while (SDL_PollEvent(&e)) { //If user closes the window if (e.type == SDL_QUIT) { quit = 0; } //If user presses any key if (e.type == SDL_KEYDOWN) { switch (e.key.keysym.sym) { case SDLK_1: useClip = 0; break; case SDLK_2: useClip = 1; break; case SDLK_3: useClip = 2; break; case SDLK_4: useClip = 3; break; case SDLK_ESCAPE: quit = 0; break; default: break; } } //If user clicks the mouse if (e.type == SDL_MOUSEBUTTONDOWN) { quit = 0; } } //Rendering SDL_RenderClear(render); //We want to tile our background so draw it 4 times renderTexture2(background, render, 0, 0, NULL); renderTexture2(background, render, bW, 0, NULL); renderTexture2(background, render, 0, bH, NULL); renderTexture2(background, render, bW, bH, NULL); //Draw the image renderTexture2(image, render, x, y, &clips[useClip]); SDL_RenderPresent(render); } //Destroy the various items cleanup_texture(image); cleanup_render(render); cleanup_window(window); IMG_Quit(); SDL_Quit(); return 0; }
六、修改SDLActivity，加载SDL2_image库：
// Load the .so static { System.loadLibrary("SDL2"); System.loadLibrary("SDL2_image"); //System.loadLibrary("SDL2_mixer"); //System.loadLibrary("SDL2_net"); //System.loadLibrary("SDL2_ttf"); System.loadLibrary("main"); }
运行截图：
