iPhone glReadPixels 问题
我正在 Iphone 中使用 OPENGL ES 绘制 PIE 字符。现在我需要检查用户单击的饼图的颜色。当我单击任何饼图时，它有时返回正确的值，有时不正确，有时只返回 0,0,0。
'(void)handleTap:(UITapGestureRecognizer *)识别器{
CGPoint lPoint = [识别器locationOfTouch:0 inView:mGLView];
字节aPixel[4]； glPixelStorei(GL_PACK_ALIGNMENT, 1); glReadPixels( lPoint.x, lPoint.y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &aPixel[0] );
NSLog(@"%i",glGetError()); NSLog(@"POINT X = %f Y = %f %d %d %d",lPoint.x, lPoint.y, aPixel[0],aPixel[1],aPixel[2]);'
I am drawing a PIE char in Iphone, with OPENGL ES. Now I need to check the color of the pie where user clicked. When I click any pie, it sometimes returns correct values, and sometimes not correct, and sometimes just returning 0,0,0.
'(void) handleTap:(UITapGestureRecognizer *) recognizer{
CGPoint lPoint = [recognizer locationOfTouch:0 inView:mGLView];
Byte aPixel[4];
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glReadPixels( lPoint.x, lPoint.y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &aPixel[0] );
NSLog(@"%i",glGetError());
NSLog(@"POINT X = %f Y = %f %d %d %d",lPoint.x, lPoint.y, aPixel[0],aPixel[1],aPixel[2]);'
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在 OpenGL 中，(0, 0) 是左下角像素。在 iOS 中，它是左上角的像素。所以你是从错误的位置阅读的。我想你想在调用 locationOfTouch:inView 之后添加：
In OpenGL, (0, 0) is the bottom left pixel. In iOS it's the top left pixel. So you're reading from the wrong location. I'd imagine you want to add, after the call to locationOfTouch:inView: