我在 Mac OS X 应用程序上使用 OpengGL 在NSOpenGLView.
该应用程序是一个电影播放器。它将电影帧解码为CVOpenGLTextureRef（这是 OpenGL 纹理），我使用GL_QUAD. 一切正常。
以下是代码的相关部分。
// "image" is the CVOpenGLTextureRef containing the movie frame as texture
GLenum textureTarget = CVOpenGLTextureGetTarget(image);
GLuint textureName = CVOpenGLTextureGetName(image);
glEnable(textureTarget);
glBindTexture(textureTarget, textureName);
glBegin(GL_QUADS);
// Draw the quads
//Note: textureTagret is NOT GL_TEXTURE_2D, therefore texture coordinates
//are NOT scaled to [0, 1]
glTexCoord2f(0.0f, imageRect.size.height);
glVertex2f (0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f);
glVertex2f (0.0f, windowRect.size.height);
glTexCoord2f(imageRect.size.width, 0.0f);
glVertex2f (windowRect.size.width, windowRect.size.height);
glTexCoord2f(imageRect.size.width, imageRect.size.height);
glVertex2f (windowRect.size.width,0.0f);
glEnd();
glDisable(textureTarget);
glFlush();
它工作得很好，我可以调整窗口大小，并且纹理正确映射到较小的窗口。
请参阅此处了解从全屏到 500x280 像素的不同窗口大小：
我现在想使用 FBO 渲染到纹理，我开始制作一个非常简单的实现，其中包括将电影帧渲染到屏幕外的 FBO（纹理），然后将该纹理绑定到屏幕上绘制。
这是代码：
// "image" is the CVOpenGLTextureRef containing the movie frame as texture
GLenum textureTarget = CVOpenGLTextureGetTarget(image);
GLuint textureName = CVOpenGLTextureGetName(image);
////////////////////////////////////////////////////////////////////
// the creation on the FBO is done only once on program start:
GLuint fboId;
GLuint textureId;
float targetWidth = 2048;
float targetHeight = 2048;
// create a texture object
glGenTextures(1, &textureId);
glBindTexture(textureTarget, textureId);
glTexParameterf(textureTarget, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(textureTarget, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(textureTarget, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameterf(textureTarget, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(textureTarget, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap
glTexImage2D(textureTarget, 0, GL_RGBA8, targetWidth, targetHeight, 0,
GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(textureTarget, 0);
// create a framebuffer object
glGenFramebuffersEXT(1, &fboId);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboId);
// attach the texture to FBO color attachment point
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
textureTarget, textureId, 0);
// check FBO status
GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
if(status != GL_FRAMEBUFFER_COMPLETE_EXT)
return FALSE;
// switch back to window-system-provided framebuffer
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
///////////////////////////////////////////////////////////////////////////////
// Render to texture
glEnable(textureTarget);
glBindTexture(textureTarget, textureName);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboId);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_QUADS);
// Draw the quads
glTexCoord2f(0.0f, imageRect.size.height);
glVertex2f (0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f);
glVertex2f (0.0f,imageRect.size.height);
glTexCoord2f(imageRect.size.width, 0.0f);
glVertex2f (imageRect.size.width, imageRect.size.height);
glTexCoord2f(imageRect.size.width, imageRect.size.height);
glVertex2f (imageRect.size.width,0.0f);
glEnd();
glFlush();
// Bind newly rendered texture
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glClear(GL_COLOR_BUFFER_BIT);
glBindTexture(textureTarget, textureId);
glGenerateMipmapEXT(textureTarget);
// draw on-screen
glBegin(GL_QUADS);
// Draw the quads
//Note: textureTagret is NOT GL_TEXTURE_2D, therefore texture coordinates
//are NOT scaled to [0, 1]
glTexCoord2f(0.0f, imageRect.size.height);
glVertex2f (0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f);
glVertex2f (0.0f, windowRect.size.height);
glTexCoord2f(imageRect.size.width, 0.0f);
glVertex2f (windowRect.size.width, windowRect.size.height);
glTexCoord2f(imageRect.size.width, imageRect.size.height);
glVertex2f (windowRect.size.width,0.0f);
glEnd();
glDisable(textureTarget);
glFlush();
代码不能正常工作，因为图像/纹理不仅是颠倒的，而且纹理映射也是错误的。只有当窗口全屏时它才能正常工作，否则它的行为真的很奇怪。
见下图：
如您所见，纹理在窗口内正确缩放，但它会根据全屏窗口大小和实际窗口大小之间的差异按比例“裁剪”。
我已经尝试了一切都没有成功。
由于这是我第一次使用 OpenGL，我是否遗漏了什么？我要疯了。。