在UIImage到纹理转换中,纹理垂直翻转

Question

我试图在iOS平台上将UIImage读入纹理.我发现StackOverflow上的代码片段可以解决这个问题,但问题是当我显示纹理时它显示为镜像倒置.

int numComponents = 4;

UIImage* image = [UIImage imageNamed:@"Test.png"];
CGImageRef imageRef = [image CGImage];
int width = CGImageGetWidth(imageRef);
int height = CGImageGetHeight(imageRef);

//Allocate texture data
GLubyte* textureData = (GLubyte *)malloc(width * height * numComponents);    

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(textureData, width, height,
                                             bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);

//texture setup
GLuint textureID;    
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &textureID);

glBindTexture(GL_TEXTURE_2D, textureID);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureDataMirrored);   

我还尝试使用以下行(在读取数据之前)镜像UIImage,但它也不起作用.实际上没有任何影响.

image = [UIImage imageWithCGImage:image.CGImage scale:image.scale orientation:UIImageOrientationUpMirrored]; 

请让我知道我在这里做错了什么.谢谢.

Answer 1

这两行解决了这个问题

CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0,height);
CGContextConcatCTM(context, flipVertical);