翻转OpenGL纹理 [英] Flipping OpenGL texture

问题描述

当我正常加载图像中的纹理时，由于OpenGL的坐标系统，它们是颠倒的。翻转它们的最佳方法是什么？

When I load textures from images normally, they are upside down because of OpenGL's coordinate system. What would be the best way to flip them?

• glScalef（1.0f，-1.0f，1.0f）;


• 反向映射纹理的y坐标


• 手动垂直翻转图像文件（在Photoshop中）


• 以编程方式翻转它们加载后（我不知道怎么做）

• glScalef(1.0f, -1.0f, 1.0f);
• mapping the y coordinates of the textures in reverse
• vertically flipping the image files manually (in Photoshop)
• flipping them programatically after loading them (I don't know how)

这是我用来加载png纹理的方法，在我的工具中.m文件（Objective-C）：

This is the method I'm using to load png textures, in my Utilities.m file (Objective-C):

+ (TextureImageRef)loadPngTexture:(NSString *)name {
    CFURLRef textureURL = CFBundleCopyResourceURL(
                                                  CFBundleGetMainBundle(),
                                                  (CFStringRef)name,
                                                  CFSTR("png"),
                                                  CFSTR("Textures"));
    NSAssert(textureURL, @"Texture name invalid");

    CGImageSourceRef imageSource = CGImageSourceCreateWithURL(textureURL, NULL);
    NSAssert(imageSource, @"Invalid Image Path.");
    NSAssert((CGImageSourceGetCount(imageSource) > 0), @"No Image in Image Source.");
    CFRelease(textureURL);

    CGImageRef image = CGImageSourceCreateImageAtIndex(imageSource, 0, NULL);
    NSAssert(image, @"Image not created.");
    CFRelease(imageSource);

    GLuint width = CGImageGetWidth(image);
    GLuint height = CGImageGetHeight(image);

    void *data = malloc(width * height * 4);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    NSAssert(colorSpace, @"Colorspace not created.");

    CGContextRef context = CGBitmapContextCreate(
                                                 data,
                                                 width,
                                                 height,
                                                 8,
                                                 width * 4,
                                                 colorSpace,
                                                 kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host);
    NSAssert(context, @"Context not created.");

    CGColorSpaceRelease(colorSpace);
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
    CGImageRelease(image);
    CGContextRelease(context);

    return TextureImageCreate(width, height, data);
}

其中TextureImage是具有height，width和void *数据的结构。

Where TextureImage is a struct that has a height, width and void *data.

现在我只是玩OpenGL，但后来我想尝试制作一个简单的2D游戏。我正在使用Cocoa进行所有窗口并使用Objective-C作为语言。

Right now I'm just playing around with OpenGL, but later I want to try making a simple 2d game. I'm using Cocoa for all the windowing and Objective-C as the language.

另外，我想知道另一件事：如果我做了一个简单的游戏，带像素映射到单位，是否可以设置它以使原点位于左上角（个人偏好），或者我会遇到其他事情的问题（例如文本渲染）？

Also, another thing I was wondering about: If I made a simple game, with pixels mapped to units, would it be alright to set it up so that the origin is in the top-left corner (personal preference), or would I run in to problems with other things (e.g. text rendering)?

谢谢。

推荐答案

Jordan Lewis指出 CGContextDrawImage在传递UIImage.CGImage时将图像颠倒绘制。在那里我找到了一个快速简单的解决方案：在调用CGContextDrawImage之前，

Jordan Lewis pointed out CGContextDrawImage draws image upside down when passed UIImage.CGImage. There I found a quick and easy solution: Before calling CGContextDrawImage,

CGContextTranslateCTM(context, 0, height);
CGContextScaleCTM(context, 1.0f, -1.0f);

这项工作是否完美。

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