为什么这个GLView屏幕截图代码返回一个空白/黑色的UIImage？(Why is this GLView Screenshot code returning a blank/black UIImage?)

 我正在使用以下代码截取GLView中的像素。 问题是，它返回一个完全黑色的UIImage 。 这个代码在LineDrawer.m中被调用，它是GLView代码的核心 - 所以它被从右边的.m文件中调用。 我怎样才能保存实际的截图而不是黑色的图像？ 
 
- (UIImage*) getGLScreenshot {

NSLog(@"1");

float scale = 0.0;
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
{
    // scale value should be 1.0 on 3G and 3GS, and 2.0 on iPhone 4.
    scale = [[UIScreen mainScreen] scale]; 
}

// these are swapped since the screen is rotatey
float h = 768 * scale;
float w = 924 * scale;

NSInteger myDataLength = w * h * 4;

// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, w, h, 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 <h; y++)
{
    for(int x = 0; x <w * 4; x++)
    {
        buffer2[(((int)h-1) - y) * (int)w * 4 + x] = buffer[y * 4 * (int)w + 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 * w;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

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

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

}

- (void)saveGLScreenshotToPhotosAlbum {
UIImageWriteToSavedPhotosAlbum([self getGLScreenshot], nil, nil, nil);
}

I am using the following code to take a screenshot of the pixels in a GLView. The problem is, it returns a completely black UIImage. This code is being called in LineDrawer.m which is the heart of the GLView code - so it is being called from the right .m file. How can I save the actual screenshot and not a black image?
 
- (UIImage*) getGLScreenshot {

NSLog(@"1");

float scale = 0.0;
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
{
    // scale value should be 1.0 on 3G and 3GS, and 2.0 on iPhone 4.
    scale = [[UIScreen mainScreen] scale]; 
}

// these are swapped since the screen is rotatey
float h = 768 * scale;
float w = 924 * scale;

NSInteger myDataLength = w * h * 4;

// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, w, h, 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 <h; y++)
{
    for(int x = 0; x <w * 4; x++)
    {
        buffer2[(((int)h-1) - y) * (int)w * 4 + x] = buffer[y * 4 * (int)w + 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 * w;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

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

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

}

- (void)saveGLScreenshotToPhotosAlbum {
UIImageWriteToSavedPhotosAlbum([self getGLScreenshot], nil, nil, nil);
}

原文：https://stackoverflow.com/questions/11168653