摘要：最近做一个涂鸦类型的产品，其中用到了涂鸦截屏的功能，因为是OpenGL做的绘制，故不能直接用简单的UIKit方式通过上下文去截屏，传统代码：

-(UIImage *)snapshotSingleView:(UIView *)view{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, NO, 0.0);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

解决：例如涂鸦、视频、地图这种OpenGL ES 方式绘制的就需要如下方式去截屏，具体代码如下：

第一步：引入头文件（搜索中大多代码都没有提到，让小伙伴们很郁闷吧）

#import <OpenGLES/ES1/glext.h>

第二步：初始化相关，这个在绘制工具类中就可以：

CAEAGLLayer *eaglLayer = (CAEAGLLayer *) self.layer;  
eaglLayer.drawableProperties = @{  
    kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],  
    kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8  
};

第三步：直接在绘制工具类中声明方面，相关代码可参考苹果官方文档：

#pragma OpenGL ES 截屏
- (UIImage *)snapshotOpenGLView{
    GLint backingWidth, backingHeight;
    // Bind the color renderbuffer used to render the OpenGL ES view
    // If your application only creates a single color renderbuffer which is already bound at this point,
    
    // this call is redundant, but it is needed if you're dealing with multiple renderbuffers.
    
    // Note, replace "viewRenderbuffer" with the actual name of the renderbuffer object defined in your class.
    
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    
    // Get the size of the backing CAEAGLLayer
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
    
    NSInteger x = 0, y = 0, width = backingWidth, height = backingHeight;
    NSInteger dataLength = width * height * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));
    
    // Read pixel data from the framebuffer
    
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    
    glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
    
    // Create a CGImage with the pixel data
    
    // If your OpenGL ES content is opaque, use kCGImageAlphaNoneSkipLast to ignore the alpha channel
    
    // otherwise, use kCGImageAlphaPremultipliedLast
    
    CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
    
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    
    CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast,ref, NULL, true, kCGRenderingIntentDefault);
    
    // OpenGL ES measures data in PIXELS
    
    // Create a graphics context with the target size measured in POINTS
    
    NSInteger widthInPoints, heightInPoints;
    
    if (NULL != &UIGraphicsBeginImageContextWithOptions) {
        
        // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
        
        // Set the scale parameter to your OpenGL ES view's contentScaleFactor
        
        // so that you get a high-resolution snapshot when its value is greater than 1.0
        
        CGFloat scale = self.contentScaleFactor;
        
        widthInPoints = width / scale;
        
        heightInPoints = height / scale;
        
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
    }
    
    else {
        // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
        widthInPoints = width;
        heightInPoints = height;
        UIGraphicsBeginImageContext(CGSizeMake(widthInPoints, heightInPoints));
    }
    
    CGContextRef cgcontext = UIGraphicsGetCurrentContext();
    
    // UIKit coordinate system is upside down to GL/Quartz coordinate system
    
    // Flip the CGImage by rendering it to the flipped bitmap context
    
    // The size of the destination area is measured in POINTS
    
    CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
    CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, widthInPoints, heightInPoints), iref);
    // Retrieve the UIImage from the current context
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    // Clean up
    
    free(data);
    CFRelease(ref);
    CFRelease(colorspace);
    CGImageRelease(iref);
    return image;
}

第四步，就可以开心的保存到相册了，代码也写下吧：

 UIImage *shareImg = [self.paintingView snapshotOpenGLView];
                                
                                UIImageWriteToSavedPhotosAlbum(shareImg,self, @selector(resultImage:didFinishSavingWithError:contextInfo:), NULL);

- (void)resultImage:(UIImage *)image didFinishSavingWithError:(NSError *)error
  contextInfo:(void *)contextInfo {
    [SVProgressHUD showSuccessWithStatus:@"保存图片到相册成功"];
    
}

总结：既然是写博客，就应该写清来龙去脉，希望能解决大家的困惑。

附效果图：