GLKit 如加载1张图片

1.初始化

-(void)setUpConfig
{
    context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES3];
    if (!context) {
    }
    [EAGLContext setCurrentContext:context];
    GLKView *view =(GLKView *) self.view;
    view.context = context;
    view.drawableColorFormat = GLKViewDrawableColorFormatRGBA8888;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat16;
    glClearColor(1, 0, 0, 1.0);
}

2.加载顶点坐标/纹理坐标

-(void)setUpVertexData
{
    GLfloat vertexData[] = {
        0.5, -0.5, 0.0f,    1.0f, 0.0f, //右下
        0.5, 0.5, -0.0f,    1.0f, 1.0f, //右上
        -0.5, 0.5, 0.0f,    0.0f, 1.0f, //左上
        -0.5, -0.5, 0.0f,   0.0f, 0.0f, //左下
        0.5, -0.5, 0.0f,    1.0f, 0.0f, //右下
        -0.5, 0.5, 0.0f,    0.0f, 1.0f, //左上
    };
    GLuint bufferID;
    glGenBuffers(1, &bufferID);
    glBindBuffer(GL_ARRAY_BUFFER, bufferID);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexData), vertexData, GL_STATIC_DRAW);

    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 5, (GLfloat *)NULL + 0);
    glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
    glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 5, (GLfloat *)NULL + 3);
}

3.加载纹理数据

-(void)setUpTexture
{
    NSString *filePath = [[NSBundle mainBundle]pathForResource:@"logo" ofType:@"png"];
    //纹理坐标原点是左下角,但是图片显示原点应该是左上角.
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:@(1),GLKTextureLoaderOriginBottomLeft, nil];
    GLKTextureInfo *textureInfo = [GLKTextureLoader textureWithContentsOfFile:filePath options:options error:nil];
    cEffect = [[GLKBaseEffect alloc]init];
    cEffect.texture2d0.enabled = GL_TRUE;
    cEffect.texture2d0.name = textureInfo.name;
}

4.代理中绘制

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
    glClear(GL_COLOR_BUFFER_BIT);
    [cEffect prepareToDraw];
    glDrawArrays(GL_TRIANGLES, 0, 6);
}

注意点：

(1) xib中的view 要继承GLKView
(2) 纹理坐标原点是左下角,但是图片显示原点应该是左上角