用下面代码加载了纹理：
CGImageRef textureImage = [UIImage imageNamed:@"apple128.png"].CGImage;
NSInteger texWidth = CGImageGetWidth(textureImage);
NSInteger texHeight = CGImageGetHeight(textureImage);
GLubyte *textureData = (GLubyte *)malloc(texWidth * texHeight * 4);
CGContextRef textureContext = CGBitmapContextCreate(
textureData,
texWidth,
texHeight,
8, texWidth * 4,
CGImageGetColorSpace(textureImage),
kCGImageAlphaPremultipliedLast);
CGContextDrawImage(textureContext,
CGRectMake(0.0, 0.0, (float)texWidth, (float)texHeight),
textureImage);
CGContextRelease(textureContext);
glGenTextures(1, &tex[0]);
glBindTexture(GL_TEXTURE_2D, tex[0]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);
free(textureData);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
然后绘制：
static const GLfloat vertices[] =
{
-30, 30, -0.0,
-30, -30, -0.0,
30, -30, -0.0,
30, 30, -0.0,
};
static const GLfloat texCoords[] =
{
0.0, 1.0,
0.0, 0.0,
1.0, 0.0,
1.0, 1.0,
};
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tex[0]);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer( 2, GL_FLOAT, 0, texCoords );
glVertexPointer(3, GL_FLOAT, 0, vertices);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
结果片是上翻转，请问，这是为什么呀？
------解决方案--------------------
因为opengl的坐标系是+y向上，图片坐标系是+y向下，你要把图片倒一下，或者把v倒一下