Xcode Screenshot EAGLContext [duplicate]

问题:

Possible Duplicate:
How to get UIImage from EAGLView?

So I was just wondering if anybody knows any way to save what is stored in an EAGLContext as a UIImage.

I am currently using:

UIGraphicsBeginImageContext(CGSizeMake(768, 1024));
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

in other apps I have and this works fine, but obviously, EAGLContext doesn't have a .layer property. I've tried casting to UIView, but that - unsurprisingly - doesn't work:

UIView *newView = [[UIView alloc] init];
newView = (UIView *)context;

I am drawing to an EAGLContext property on a UIView (technically an EAGLContext on a UIView on another UIView on a View Controller, but I figure that shouldn't make any difference) using OpenGLES 1.

If anybody knows anything about this, even if its just that I'm completely barking up an impossible tree, please let me know!

Matt

回答1:

After a few days I finally got a working solution to this. There is code provided by Apple which produces an UIImage from an EAGLView. Then you simply need to flip the image vertically since UIKit is upside down. The link to the documentation where I found this method doesn't exist anymore.

Method to capture EAGLView:

-(UIImage *)drawableToCGImage 
{
    GLint backingWidth2, backingHeight2;
    //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 "_colorRenderbuffer" 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, &backingWidth2);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight2);

    NSInteger x = 0, y = 0, width2 = backingWidth2, height2 = backingHeight2;
    NSInteger dataLength = width2 * height2 * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

    // Read pixel data from the framebuffer
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(x, y, width2, height2, 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(width2, height2, 8, 32, width2 * 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 = width2 / scale;
        heightInPoints = height2 / scale;
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
    }
    else {
        // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
        widthInPoints = width2;
        heightInPoints = height2;
        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;
}

Method to flip the image vertically:

- (UIImage *)flipImageVertically:(UIImage *)originalImage 
{
    UIImageView *tempImageView = [[UIImageView alloc] initWithImage:originalImage];
    UIGraphicsBeginImageContext(tempImageView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGAffineTransform flipVertical = CGAffineTransformMake(
                                                           1, 0, 0, -1, 0, tempImageView.frame.size.height
                                                           );
    CGContextConcatCTM(context, flipVertical);

    [tempImageView.layer renderInContext:context];

    UIImage *flippedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    //[tempImageView release];

    return flippedImage;
}