使用 GL 缓冲区中的每像素 alpha 创建 UIImage
我试图获取我的 gl 缓冲区并将其转换为 UIImage,同时保留该 gl 缓冲区中的每像素 alpha。它似乎不起作用,因为我得到的结果是没有 alpha 的缓冲区。有人可以帮忙吗?我觉得我一定在某个地方错过了几个关键步骤。我真的很乐意对此提出任何建议。
基本上我是这样做的:
//Read Pixels from OpenGL
glReadPixels(0, 0, miDrawBufferWidth, miDrawBufferHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
//Make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, len, NULL);
//Configure image
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(miDrawBufferWidth, miDrawBufferHeight, 8, 32, (4 * miDrawBufferWidth), colorSpaceRef, kCGBitmapByteOrderDefault, provider, NULL, NO, kCGRenderingIntentDefault);
// use device's orientation's width/height to determine context dimensions (and consequently resulting image's dimensions)
uint32* pixels = (uint32 *) IQ_NEW(kHeapGfx, "snapshot_pixels") GLubyte[len];
// use kCGImageAlphaLast? :-/
CGContextRef context = CGBitmapContextCreate(pixels, iRotatedWidth, iRotatedHeight, 8, (4 * iRotatedWidth), CGImageGetColorSpace(iref), kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, miDrawBufferWidth, miDrawBufferHeight), iref);
UIImage *outputImage = [[UIImage alloc] initWithCGImage:CGBitmapContextCreateImage(context)];
//cleanup
CGDataProviderRelease(provider);
CGImageRelease(iref);
CGContextRelease(context);
return outputImage;
I'm trying to take my gl buffer and turn it into a UIImage while retaining the per-pixel alpha within that gl buffer. It doesn't seem to work, as the result I'm getting is the buffer w/o alpha. Can anyone help? I feel like I must be missing a few key steps somewhere. I would really love any advice on this.
Basically I do:
//Read Pixels from OpenGL
glReadPixels(0, 0, miDrawBufferWidth, miDrawBufferHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
//Make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, len, NULL);
//Configure image
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(miDrawBufferWidth, miDrawBufferHeight, 8, 32, (4 * miDrawBufferWidth), colorSpaceRef, kCGBitmapByteOrderDefault, provider, NULL, NO, kCGRenderingIntentDefault);
// use device's orientation's width/height to determine context dimensions (and consequently resulting image's dimensions)
uint32* pixels = (uint32 *) IQ_NEW(kHeapGfx, "snapshot_pixels") GLubyte[len];
// use kCGImageAlphaLast? :-/
CGContextRef context = CGBitmapContextCreate(pixels, iRotatedWidth, iRotatedHeight, 8, (4 * iRotatedWidth), CGImageGetColorSpace(iref), kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, miDrawBufferWidth, miDrawBufferHeight), iref);
UIImage *outputImage = [[UIImage alloc] initWithCGImage:CGBitmapContextCreateImage(context)];
//cleanup
CGDataProviderRelease(provider);
CGImageRelease(iref);
CGContextRelease(context);
return outputImage;
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是的!幸运的是,显然有人在这里解决了这个问题: http: //www.iphonedevsdk.com/forum/iphone-sdk-development/23525-cgimagecreate-alpha.html
它归结为一个额外的 kCGImageAlphaLast 标志被传递到 CGImageCreate 中以合并 alpha(以及 kCGBitmapByteOrderDefault 标志) )。 :)
Yes! Luckily apparently someone has solved this exact problem here: http://www.iphonedevsdk.com/forum/iphone-sdk-development/23525-cgimagecreate-alpha.html
It boiled down to an extra kCGImageAlphaLast flag being passed into the CGImageCreate to incorporate the alpha (along with the kCGBitmapByteOrderDefault flag). :)