- (UIView *)hitTest:(CGPoint)point withEvent:(nullable UIEvent *)event{
    
    //apple文档描述，不接受事件的情况
    if (self.userInteractionEnabled == NO || self.isHidden == YES || self.alpha < 0.01) {
        return nil;
    }
    
    //如果当前View包含此Point
    if ([self pointInside:point withEvent:event]) {
        
        //遍历子View，这里注意要从后往前遍历，因为后面的是越靠近用户的
        for (NSInteger i=self.subviews.count-1; i>=0; i--) {
            
            UIView* subView = [self.subviews objectAtIndex:i];
            
            //将父View的Point转换成子View坐标系的Point
            CGPoint pointInSubView = [subView convertPoint:point fromView:self];
            
            //递归子View调用HitTest:
            UIView* resultView = [subView hitTest:pointInSubView withEvent:event];
            
            //找到了子View可以响应
            if (resultView) {
                return resultView;
            }
            
        }
        
        //没有找到可以响应的子View，返回自己
        return self;
    }
    
    //返回nil，告诉上一级自己无法响应此事件
    return nil;
}

attribute vec2 TexCoordIn; // New
varying vec2 TexCoordOut; // New

void main(void) { 
    DestinationColor = SourceColor; 
    gl_Position = Projection * Modelview * Position;
    TexCoordOut = TexCoordIn; // New
}

varying lowp vec4 DestinationColor;
varying lowp vec2 TexCoordOut; // New
uniform sampler2D Texture; // New

void main(void) {
    gl_FragColor = DestinationColor * texture2D(Texture, TexCoordOut); // New
}

+ (GLuint)createTextureWithImage:(UIImage *)image{
    
    //转换为CGImage，获取图片基本参数
    CGImageRef cgImageRef = [image CGImage];
    GLuint width = (GLuint)CGImageGetWidth(cgImageRef);
    GLuint height = (GLuint)CGImageGetHeight(cgImageRef);
    CGRect rect = CGRectMake(0, 0, width, height);
    
    //绘制图片
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    void *imageData = malloc(width * height * 4);
    CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, width * 4, colorSpace,kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGContextTranslateCTM(context, 0, height);
    CGContextScaleCTM(context, 1.0f, -1.0f);
    CGColorSpaceRelease(colorSpace);
    CGContextClearRect(context, rect);
    CGContextDrawImage(context, rect, cgImageRef);
    
    GLuint textureID;
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_2D, textureID);
    
    //纹理一些设置，可有可无
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
    
    glBindTexture(GL_TEXTURE_2D, 0);
    
    //释放内存
    CGContextRelease(context);
    free(imageData);
    
    return textureID;
}

glActiveTexture(GL_TEXTURE0);
//载入纹理
glBindTexture(GL_TEXTURE_2D, _textTureId);

glUniform1i(_textureSlot, 0);

const GLfloat texCoords[] = {
    0, 0,//左下
    1, 0,//右下
    0, 1,//左上
    1, 1,//右上
};
glVertexAttribPointer(_textureCoordsSlot, 2, GL_FLOAT, GL_FALSE, 0, texCoords);
glEnableVertexAttribArray(_textureCoordsSlot);

//获取一个操作句柄
glGenBuffers(1, &_vertexBuffer);
//设置缓存对象类型，数据缓存对象，还是元素缓存对象，通俗的说就是数组还是索引
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
//分配内存空间
glBufferData(GL_ARRAY_BUFFER, 7*3*sizeof(GLfloat), vertices, GL_STATIC_DRAW);

在绘制代码Draw时，可以使用，绘制代码与正常并无冥想差别
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 7*sizeof(float), 0);
glEnableVertexAttribArray(_positionSlot);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _triangleIndexBuffer);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_BYTE, 0);

//可以在清理时，释放VBO
glDeleteBuffers(1, &_vertexBuffer);
_vertexBuffer = 0;

glDeleteBuffers(1, &_triangleIndexBuffer);
_triangleIndexBuffer = 0;

- (void)setupLayer{

    CAEAGLLayer* layer = (CAEAGLLayer*)self.layer;
    
    layer.opaque = YES;
    
    layer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:@(NO), kEAGLDrawablePropertyRetainedBacking,
                                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
}

_context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2];

- (void)drawFrame{

    [_eaglView setFramebuffer];
    
    [_eaglView draw];
    
    [_eaglView presentFramebuffer];
}

- (void)createBuffer{
    
    [self checkContext];
    
    glGenRenderbuffers(1, &_colorRenderBuffer);
    
    glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
    
    [_context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];
    
    glGenFramebuffers(1, &_frameBuffer);
    
    glBindFramebuffer(GL_FRAMEBUFFER, _frameBuffer);
    
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
    						GL_RENDERBUFFER, _colorRenderBuffer);
}

- (void)deleteBuffer{

    [self checkContext];
    
    glDeleteRenderbuffers(1, &_colorRenderBuffer);
    
    _colorRenderBuffer = 0;
    
    glDeleteFramebuffers(1, &_frameBuffer);
    
    _frameBuffer = 0;
}

- (void)setFramebuffer
{
    if ([self checkContext])
    {
        if (!_frameBuffer){
            [self createBuffer];
        }
        glBindFramebuffer(GL_FRAMEBUFFER, _frameBuffer);
    }
}

- (BOOL)presentFramebuffer
{
    BOOL success = FALSE;
    
    if ([self checkContext])
    {
        glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
        
        success = [_context presentRenderbuffer:GL_RENDERBUFFER];
    }
    return success;
}

- (void)draw{
    //设置背景颜色为绿色
    glClearColor(0, 1.0, 0,1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    //设置管区域大小
    glViewport(0, 0, self.frame.size.width, self.frame.size.height);
    
    GLfloat vertices[] = {
        0.0f,  0.5f, 0.0f,
        -0.5f, -0.5f, 0.0f,
        0.5f,  -0.5f, 0.0f };
    //设置着色器中的vPositon
    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 0, vertices);
    //使上一步的设置生效
    glEnableVertexAttribArray(_positionSlot);
    //绘制三角形
    glDrawArrays(GL_TRIANGLES, 0, 3);
}