iOS OpenGL ES简单绘制纹理

  

OpenGL 中任何复杂的图形都是由点,线 和三角形组成的. 那么一个矩形 就需要有两个三角形组成.

纹理, 可以理解为一张图片, 我么可以将整张or部分图片绘制到圆形, 矩形等目标图形中. 

下图表示了顶点数据 对应 的纹理中的点.

左侧代表定点数据, 其坐标原点是屏幕中央 ; 右侧图片(纹理), 坐标原点是左下角

GLKBaseEffect让我们避开了写shader Language 着色器语言, 相当于对glsl的封装

typedef struct {
    GLKVector3 positonCoords;//顶点
    GLKVector2 textureCoords;//纹理
}SceneVertex;

@interface GLViewController ()

@property(nonatomic,strong)GLKBaseEffect *baseEffect;
@property(nonatomic,assign)GLuint vertexBufferID;//缓存ID属性

@end

@implementation GLViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    //1.创建OpenGLE ES上下文
    GLKView *view = (GLKView *)self.view;
    view.context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];
    [EAGLContext setCurrentContext:view.context];
    
    //2.GLKBaseEffect属性, 使我们不需要编写shader language(着色器)代码就可以简单完成绘制
    self.baseEffect = [[GLKBaseEffect alloc]init];
    self.baseEffect.useConstantColor = GL_TRUE;//使用静态颜色绘制
    self.baseEffect.constantColor = GLKVector4Make(1.0f, 1.0f, 1.0f, 1.0f);//设置绘制颜色 rgba
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);//背景颜色
    
    //3.定点数据
    //矩形的六个顶点
    static const SceneVertex vertices[] = {
        {{1, -1, 0.0f,},{1.0f,0.0f}}, //右下
        {{1, 1,  0.0f},{1.0f,1.0f}}, //右上
        {{-1, 1, 0.0f},{0.0f,1.0f}}, //左上
        
        {{1, -1, 0.0f},{1.0f,0.0f}}, //右下
        {{-1, 1, 0.0f},{0.0f,1.0f}}, //左上
        {{-1, -1, 0.0f},{0.0f,0.0f}}, //左下
    };
    
    //4.生成缓存,并为缓存提供数据
    glGenBuffers(1, &_vertexBufferID);//申请一个标识符
    glBindBuffer(GL_ARRAY_BUFFER, _vertexBufferID);//将标识符绑定到GL_ARRAY_BUFFER
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//复制定点数据从CPU 到 GPU
    
    glEnableVertexAttribArray(GLKVertexAttribPosition);//顶点缓存数据
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(SceneVertex), NULL + offsetof(SceneVertex, positonCoords));
    glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
    glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(SceneVertex), NULL + offsetof(SceneVertex, textureCoords));

    
    //5.生成纹理
    //使用GLkit中的GLKTextureInfo方便的生成图片纹理。
    CGImageRef imageRef = [[UIImage imageNamed:@"1.png"]CGImage];
    //GLKTextureInfo封装了纹理缓存的信息，包括是否包含MIP贴图
    //option 防止图片是倒立了，这个是因为CoreGraphics的坐标系问题
    NSDictionary* options = [NSDictionary dictionaryWithObjectsAndKeys:@(1), GLKTextureLoaderOriginBottomLeft, nil];
    GLKTextureInfo *textureInfo = [GLKTextureLoader textureWithCGImage:imageRef options:options error:nil];
    self.baseEffect.texture2d0.name = textureInfo.name;
    self.baseEffect.texture2d0.target = textureInfo.target;
    
    //6.代理, 绘制
    
}

//系统给我们回调的绘制消息，该方法会一直被调用，和display方法一致
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect{
   
    //清除背景色
    glClearColor(0.0f,0.0f,0.0f,1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    [self.baseEffect prepareToDraw];
    glDrawArrays(GL_TRIANGLES, 0, 6);
    
}

- (void)dealloc{
    GLKView *view = (GLKView *)self.view;
    [EAGLContext setCurrentContext:view.context];
    if (_vertexBufferID != 0) {
        glDeleteBuffers(1, &_vertexBufferID);
        _vertexBufferID = 0;
    }
    
    
}



@end