glReadPixel为iPhone 6返回不正确的图像，但适用于iPad和iPhone 5

Question

我使用以下代码从OpenGL ES场景中读取图像：

- (UIImage *)drawableToCGImage
{
CGRect myRect = self.bounds;
NSInteger myDataLength = myRect.size.width * myRect.size.height * 4;
glFinish();
glPixelStorei(GL_PACK_ALIGNMENT, 4);
int width = myRect.size.width;
int height = myRect.size.height;
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer2);
for(int y1 = 0; y1 < height; y1++) {
    for(int x1 = 0; x1 < width * 4; x1++) {
        buffer[(height - 1 - y1) * width * 4 + x1] = buffer2[y1 * 4 * width + x1];
    }
}
free(buffer2);
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, NULL);
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * myRect.size.width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGImageRef imageRef = CGImageCreate(myRect.size.width, myRect.size.height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
UIImage *image = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
return image;
}

它非常适合iPad和旧iPhone版本，但我注意到在iPhone 6（设备和模拟器）上，它看起来像单色故障。会是什么？

另外，这是我的CAEAGLLayer属性代码：

eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                @YES, kEAGLDrawablePropertyRetainedBacking,
                                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

请问有人能揭示这个疯狂的魔法吗？

Answer 1

多亏了

@MaticOblak，我才想出了问题所在。

缓冲区填充不正确，因为矩形大小的浮点值未正确舍入（是的，仅适用于 iPhone 6 尺寸）。应改用整数值。

UPD：我的问题已使用以下代码修复：

GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);
int width = viewport[2];
int height = viewport[3];