如何将OpenGL视图捕获为UIImage？

Question

当我尝试使用这种方法将OpenGL视图转换为UIImage时，只返回了视图的背景，而不是GLView内容。如何将OpenGL的上下文转换为UIImage？

- ohho

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我曾经遇到过同样的问题，但是在这里提供的答案下，我得到了一个黑屏。请查看我的回答以了解我最终如何使其工作。 http://stackoverflow.com/questions/11036288/xcode-screenshot-eaglcontext/11868013#11868013 - Nate_Hirsch

Answer 1

这要看你使用的OpenGL视图。从iOS 5开始，你可以使用GLKit和相应的GLKView来大大简化呈现UIImage的过程。

GLKView* v = (GLKView*) _previewViewController.view;
UIImage* thumbnail = [v snapshot];

http://developer.apple.com/library/ios/#documentation/GLkit/Reference/GLKView_ClassReference/Reference/Reference.html

- Christoph

Answer 2

使用以下代码将您的opengl视图转换为UIImage。

GLubyte *buffer = (GLubyte *) malloc(backingWidth * backingHeight * 4);
 GLubyte *buffer2 = (GLubyte *) malloc(backingWidth * backingHeight * 4);
 GLvoid *pixel_data = nil;
 glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE,
         (GLvoid *)buffer);
for (int y=0; y<backingHeight; y++) {
     for (int x=0; x<backingWidth*4; x++) {
         buffer2[y * 4 * backingWidth + x] =
     buffer[(backingHeight - y - 1) * backingWidth * 4 + x];
     }
 }
 CGDataProviderRef provider;
 provider = CGDataProviderCreateWithData(NULL, buffer2,
                                          backingWidth * backingHeight * 4,
                                          freeImageData);
 // set up for CGImage creation
 int bitsPerComponent = 8;
 int bitsPerPixel = 32;
 int bytesPerRow = 4 * backingWidth;
 CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
 CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
 // Use this to retain alpha
 //CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
 CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
 CGImageRef imageRef = CGImageCreate(backingWidth, backingHeight,
                                 bitsPerComponent, bitsPerPixel,
                                 bytesPerRow, colorSpaceRef,
                                 bitmapInfo, provider,
                                 NULL, NO,
                                 renderingIntent);
 // this contains our final image.
 UIImage *newUIImage = [UIImage imageWithCGImage:imageRef];

Taken from

- Jhaliya - Praveen Sharma

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这会渲染黑色背景。有人能帮我看看为什么吗？ - Narek Safaryan

Answer 3

感谢提供代码。我发现它很有用，但是为了正确释放缓冲区、缓冲区2、图像引用、颜色空间引用和提供程序指针所分配的内存，我需要添加一些额外的代码。请注意，使用提供程序释放函数来释放缓冲区2。

static void myProviderReleaseData (void *info,const void *data,size_t size)
{
    free((void*)data);
}

- (UIImage*)renderToImage
{
    // The image size should be grabbed from your ESRenderer class. 
    // That parameter is get in renderer function: 
    // - (BOOL) resizeFromLayer:(CAEAGLLayer *)layer {
    // glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    GLint backingWidth = renderer.backingWidth;
    GLint backingHeight = renderer.backingHeight;

    GLubyte *buffer = (GLubyte *) malloc(backingWidth * backingHeight * 4);
    GLubyte *buffer2 = (GLubyte *) malloc(backingWidth * backingHeight * 4);

    glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE,
                 (GLvoid *)buffer);
    for (int y=0; y<backingHeight; y++) {
        for (int x=0; x<backingWidth*4; x++) {
            buffer2[y * 4 * backingWidth + x] =
            buffer[(backingHeight - y - 1) * backingWidth * 4 + x];
        }
    }
    free(buffer);
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2,
                                            backingWidth * backingHeight * 4,
                                        myProviderReleaseData);
    // set up for CGImage creation
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * backingWidth;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    // Use this to retain alpha
    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    CGImageRef imageRef = CGImageCreate(backingWidth, backingHeight,
                                        bitsPerComponent, bitsPerPixel,
                                    bytesPerRow, colorSpaceRef,
                                    bitmapInfo, provider,
                                    NULL, NO,
                                    renderingIntent);
    // this contains our final image.
    UIImage *newUIImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);

    return newUIImage;
}   

- Krešimir Prcela

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这会在图层上呈现黑色背景，而我已经在initWithCoder中将图层背景设置为透明颜色了。 - manishnath