iOS：关于在屏幕上渲染纹理的纹理坐标的混乱
我正在尝试在 iPhone 屏幕上渲染由相机生成的纹理。 我从 Brad Larson 下载了颜色跟踪示例 http://www.sunsetlakesoftware.com/2010/10/22/gpu-accelerated-video-processing-mac-and-ios（示例代码的直接链接：http://www.sunsetlakesoftware.com/sites/default/files/ColorTracking.zip）。
在 ColorTrackingViewController drawFrame 方法中，他使用以下代码生成顶点和相应的纹理坐标以渲染纹理正方形：
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f,
};
static const GLfloat textureVertices[] = {
1.0f, 1.0f,
1.0f, 0.0f,
0.0f, 1.0f,
0.0f, 0.0f,
};
我不明白为什么这些纹理坐标可以正常工作。
在我看来，在我看到的另一个示例代码中也可以正常工作，它们应该是：
static const GLfloat textureVertices[] = {
0.0f, 1.0f,
1.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
};
我浏览了整个代码，但我无法弄清楚为什么上面的纹理坐标可以正常工作。我缺少什么？
I am trying to render a texture that was generated by the camera on the iPhone screen.
I downloaded the color tracking example from Brad Larson on http://www.sunsetlakesoftware.com/2010/10/22/gpu-accelerated-video-processing-mac-and-ios (direct link for sample code: http://www.sunsetlakesoftware.com/sites/default/files/ColorTracking.zip).
In the ColorTrackingViewController drawFrame method he uses the following code to generate vertex and corresponding texture coordinates for rendering a textured square:
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f,
};
static const GLfloat textureVertices[] = {
1.0f, 1.0f,
1.0f, 0.0f,
0.0f, 1.0f,
0.0f, 0.0f,
};
I don't understand why these texture coordinates work correctly.
In my opinion, and in another example code I have seen that works also correctly, they should be:
static const GLfloat textureVertices[] = {
0.0f, 1.0f,
1.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
};
I went through the whole code, but I cannot figure out why the above texture coordinates work correctly. What am I missing?
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我相信这是因为 iPhone 摄像头的图像数据总是逆时针旋转 90 度呈现。为了抵消这种旋转，他还将纹理坐标设置为逆时针旋转 90 度。有时两个错误确实可以构成一个正确？
I believe it is because the image data from the iphone camera is always presented rotated 90 CCW. To counteract that rotation he's setting the texture co-ordinates to be rotated 90 CCW too. Sometimes two wrongs do make a right?