iOS开发- OpenGL ES屏幕截图

之前写过一个常规的屏幕截图:http://blog.csdn.net/hitwhylz/article/details/17189351

可是发现这个办法对于OpenGL 无用。  获取到的数据为空。

所以这里介绍下OpenGL ES屏幕截图。

1.初始化。

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

2.声明方法。

- (UIImage*)snapshot:(UIView*)eaglview
{
    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 = eaglview.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;
}

3.使用

调用上述的方法就可以。

- (UIImage*)snapshot:(UIView*)eaglview