iphone opengl es 截图

 

Anyway, for an app I’m working on, I needed to take a screenshot of OpenGL ES rendered content. I assumed there was some built in function for that, but much searching led me to the conclusion that it’s a roll-your-own kind of thing. So, after a couple of days, I was finally able to piece together at least three or four different semi-working solutions from various forums and mailing lists, combined with some hacking about, to come up with a solution that actually works.
The first and last steps are easy.
First step, you read the GL data into a raw byte array with glReadPixels. Simple enough.
Last step, you save a UIImage to the Photo Album with UIImageWriteToSavedPhotosAlbum.
The tough part is getting that byte array into a UIImage. My first attempt was to use [UIImage imageFromData:data]. But the problem with that is that that method expects data to be in a file format of one of the supported image types of UIImage, whereas glReadPixels is just raw pixel data.
Digging around some more, I found [UIImage imageWithCGImage:imageRef]. You can get a CGImageRef with CGImageCreate.
CGImageCreate requires a CGDataProviderRef. And you can create one of those with CGDataProviderCreateWithData, using the results from glReadPixels! Finally, a path from one end to the other.
glReadPixels -> CGDataProviderCreateWithData -> CGImageCreate -> [UIImage imageWithCGImage:] -> UIImageWriteToSavedPhotosAlbum
Yay!
But wait. One more snag. OpenGL uses standard Cartesian coordinates. In other words, +Y is up, -Y is down. So the byte array you get with glReadPixels (and thus your final image) will be upside down. A bit of fancy bit-twiddling fixed that up. Here are the final methods, meant to be used within a UIView with a CAEAGLLayer class (just like the EAGL class in the OpenGL ES template file).

-(UIImage *) glToUIImage {
    NSInteger myDataLength = 320 * 480 * 4;

    // allocate array and read pixels into it.
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, 320, 480, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    // gl renders "upside down" so swap top to bottom into new array.
    // there's gotta be a better way, but this works.
    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
    for(int y = 0; y <480; y++)
    {
        for(int x = 0; x <320 * 4; x++)
        {
            buffer2[(479 - y) * 320 * 4 + x] = buffer[y * 4 * 320 + x];
        }
    }

    // make data provider with data.
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);

    // prep the ingredients
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * 320;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    // make the cgimage
    CGImageRef imageRef = CGImageCreate(320, 480, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);

    // then make the uiimage from that
    UIImage *myImage = [UIImage imageWithCGImage:imageRef];
    return myImage;
}

-(void)captureToPhotoAlbum {
    UIImage *image = [self glToUIImage];
    UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);
}