Question

When I try to use this method to convert a OpenGL view to UIImage, only the view’s background is returned, but not the GLView content. How can I convert OpenGL’s context into a UIImage?

Answer 1

Use the below code to convert your opengl view in 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