我正在尝试在 iPhone 上开发一个复杂的绘画应用程序。我目前正在使用 Quartz 进行绘图（例如 CGContext...）。不幸的是，Quartz 开销对于我正在做的绘图类型来说太慢了，我正在使用 GLPaint 示例作为参考点移植到 OpenGL 调用。
有没有办法从 EAGLview 类中获取 UIImage/CGImage（相当于 Quartz 的 UIGraphicsGetImageFromCurrentImageContext）？基本上我需要保存GLPaint应用程序绘制的图片。
【问题讨论】：
标签： iphone objective-c opengl-es quartz-graphics
-(UIImage *) saveImageFromGLView
{
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;
}
【讨论】：
与@Quakeboy 的答案相同，但传入视图以便动态确定大小（我将其用于我的通用应用程序）：
- (UIImage *)saveImageFromGLView:(UIView *)glView {
int width = glView.frame.size.width;
int height = glView.frame.size.height;
NSInteger myDataLength = width * height * 4;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, width, height, 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 < height; y++)
{
for(int x = 0; x < width * 4; x++)
{
buffer2[((height - 1) - y) * width * 4 + x] = buffer[y * 4 * width + 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 * width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// then make the uiimage from that
UIImage *myImage = [UIImage imageWithCGImage:imageRef];
return myImage;
}
【讨论】：
这绝对是可能的。诀窍是使用 glReadPixels 将图像数据从 OpenGL 帧缓冲区中提取到您可以使用的内存中。一旦有了指向图像数据的指针，就可以使用 CGDataProviderCreateWithData 和 CGImageCreate 从数据中创建 CGImage。我正在开发一个基于 OpenGL 的绘图应用程序，该应用程序大量使用了这种技术！
【讨论】：
此代码不会像上述解决方案那样泄漏内存，并且会考虑动态视图大小以及视网膜与标准显示器：
-(BOOL)iPhoneRetina{
return ([[UIScreen mainScreen] respondsToSelector:@selector(displayLinkWithTarget:selector:)] && ([UIScreen mainScreen].scale == 2.0))?YES:NO;
}
void releasePixels(void *info, const void *data, size_t size) {
free((void*)data);
}
-(UIImage *) glToUIImage{
int imageWidth, imageHeight;
int scale = [self iPhoneRetina]?2:1;
imageWidth = self.frame.size.width*scale;
imageHeight = self.frame.size.height*scale;
NSInteger myDataLength = imageWidth * imageHeight * 4;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, imageWidth, imageHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, releasePixels);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * imageWidth;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
UIImage *myImage = [UIImage imageWithCGImage:imageRef scale:scale orientation:UIImageOrientationDownMirrored]; //Render image flipped, since OpenGL's data is mirrored
CGImageRelease(imageRef);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
return myImage;
}
其他的泄漏内存是因为 CGDataProviderCreateWithData 的最后一个参数应该是一个释放内存的函数，而且他们也省略了 CGRelease 函数。
【讨论】：
void SaveScreenImage()
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
CGImageRef cgImage = UIGetScreenImage();
void *imageBytes = NULL;
if (cgImage == NULL) {
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
imageBytes = malloc(320 * 480 * 4);
CGContextRef context = CGBitmapContextCreate(imageBytes, 320, 480, 8, 320 * 4, colorspace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorspace);
for (UIWindow *window in [[UIApplication sharedApplication] windows]) {
CGRect bounds = [window bounds];
CALayer *layer = [window layer];
CGContextSaveGState(context);
if ([layer contentsAreFlipped]) {
CGContextTranslateCTM(context, 0.0f, bounds.size.height);
CGContextScaleCTM(context, 1.0f, -1.0f);
}
[layer renderInContext:(CGContextRef)context];
CGContextRestoreGState(context);
}
cgImage = CGBitmapContextCreateImage(context);
CGContextRelease(context);
}
UIImage *image=[UIImage imageWithCGImage:cgImage];
UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);
[pool release];
}
此代码将保存为您在屏幕上看到的内容。但它可能是私有 api。
【讨论】：