设置 OpenGL 多渲染目标 [英] Setting up OpenGL Multiple Render Targets
问题描述
我已经看过很多关于这个主题的材料，但是我发现的示例之间存在一些差异，而且我很难对正确的过程有深入的了解.希望有人能告诉我我是否在正确的轨道上.我还应该提到我在 OS X Snow Leopard 和最新版本的 Xcode 3 上这样做.
I've seen a lot of material on this subject, but there are some differences between the examples I've found and I'm having a hard time getting a solid understanding of the correct process. Hopefully someone can tell me if I'm on the right track. I should also mention I'm doing this on OS X Snow Leopard and the latest version of Xcode 3.
举个例子，假设我想写两个目标，一个是正常的，一个是彩色的.为此，我创建了一个帧缓冲区并为其绑定了两个纹理以及一个深度纹理:
For the sake of example, let's say that I want to write to two targets, one for normal and one for color. To do this I create one framebuffer and bind two textures to it, as well as a depth texture:
glGenFramebuffersEXT(1, &mFBO);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, mFBO);
glGenTextures(1, &mTexColor);
glBindTexture(GL_TEXTURE_2D, mTexColor);
//<texture params>
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, mTexColor, 0);
glGenTextures(1, &mTexNormal);
glBindTexture(GL_TEXTURE_2D, mTexNormal);
//<Texture params>
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT1_EXT, GL_TEXTURE_2D, mTexNormal, 0);
glGenTextures(1, &mTexDepth);
glBindTexture(GL_TEXTURE_2D, mTexDepth);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT24, w, h, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_TEXTURE_2D, mTexDepth, 0);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0)
在渲染之前，我会再次绑定帧缓冲区然后执行:
Before rendering, I would bind the framebuffer again and then do:
GLenum buffers[] = { GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT };
glDrawBuffers(2, buffers);
这意味着进一步的绘制调用将绘制到我的帧缓冲区.(我觉得?)
This would mean further draw calls would draw to my framebuffer. (I think?)
然后我会设置我的着色器并绘制场景.在我的顶点着色器中，我会像往常一样处理法线/位置/颜色，并将数据传递给片段着色器.然后片段将执行以下操作:
I'd then set my shaders and draw the scene. In my vertex shader I would process normals/positions/colors as usual, and pass the data to the fragment shader. The fragment would then do something like:
gl_FragData[0] = OutputColor;
gl_FragData[1] = OutputNormal;
此时，我应该有两个纹理；一种具有来自所有渲染对象的颜色，一种具有法线.所有这些都是正确的吗?我现在应该可以像使用其他纹理一样使用这些纹理，比如将它们渲染为全屏四边形，对吗?
At this point, I should have two textures; one with colors from all the rendered objects and one with normals. Is all of this correct? I should now be able to use those textures like any other, say rendering them to a fullscreen quad, right?
推荐答案
听起来和看起来都很合理.这确实是常见的做法.如果您不需要深度数据作为纹理进行进一步处理，您也可以将渲染缓冲区用于附件，但纹理也应该可以正常工作.
Sounds and looks reasonable. This is indeed the common way to do it. If you don't need the depth data as texture for further processing, you can also use a renderbuffer for an attachment, but a texture should also work fine.
您还可以在所有设置完成后使用 glCheckFramebufferStatusEXT 来查看帧缓冲区在其当前配置中是否有效，但您的代码看起来不错.如果您没有问题并且这只是为了保证，那么请放心，您走在正确的轨道上，否则请告诉我们出了什么问题.
You can also use glCheckFramebufferStatusEXT after all the setup is done, to see if the framebuffer is valid in its current configuration, but your code looks fine. If you don't have a problem and this was just for assurance, then rest assured that you're on the right track, otherwise tell us what's wrong.
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