OpenGL MSAA以两种不同的方式。有什么不同吗？

Question

我一直在寻找OpenGL多样本反走样教程，我发现了许多，但我将采取2。

他们用不同的方式来做这件事。我已经测试了这两种方式，都为我的项目工作，所以我可以使用它们中的任何一种。

我用这个把我的游戏引擎场景渲染成纹理。

这是第一条路：

用MSAA创建FBO

// create a texture object
glGenTextures(1, &textureId);
glBindTexture(GL_TEXTURE_2D, textureId);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glBindTexture(GL_TEXTURE_2D, 0);

// create a MSAA framebuffer object
// NOTE: All attachment images must have the same # of samples.
// Ohterwise, the framebuffer status will not be completed.
glGenFramebuffers(1, &fboMsaaId);
glBindFramebuffer(GL_FRAMEBUFFER, fboMsaaId);

// create a MSAA renderbuffer object to store color info
glGenRenderbuffers(1, &rboColorId);
glBindRenderbuffer(GL_RENDERBUFFER, rboColorId);
glRenderbufferStorageMultisample(GL_RENDERBUFFER, MSAA_level, GL_RGB8, width, height);
glBindRenderbuffer(GL_RENDERBUFFER, 0);

// create a MSAA renderbuffer object to store depth info
// NOTE: A depth renderable image should be attached the FBO for depth test.
// If we don't attach a depth renderable image to the FBO, then
// the rendering output will be corrupted because of missing depth test.
// If you also need stencil test for your rendering, then you must
// attach additional image to the stencil attachement point, too.
glGenRenderbuffers(1, &rboDepthId);
glBindRenderbuffer(GL_RENDERBUFFER, rboDepthId);
glRenderbufferStorageMultisample(GL_RENDERBUFFER, MSAA_level, GL_DEPTH_COMPONENT, width, height);
glBindRenderbuffer(GL_RENDERBUFFER, 0);

// attach msaa RBOs to FBO attachment points
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rboColorId);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboDepthId);


// create a normal (no MSAA) FBO to hold a render-to-texture
glGenFramebuffers(1, &fboId);
glBindFramebuffer(GL_FRAMEBUFFER, fboId);

glGenRenderbuffers(1, &rboId);
glBindRenderbuffer(GL_RENDERBUFFER, rboId);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);
glBindRenderbuffer(GL_RENDERBUFFER, 0);

// attach a texture to FBO color attachement point
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureId, 0);

// attach a rbo to FBO depth attachement point
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboId);

//@@ disable color buffer if you don't attach any color buffer image,
//@@ for example, rendering the depth buffer only to a texture.
//@@ Otherwise, glCheckFramebufferStatus will not be complete.
//glDrawBuffer(GL_NONE);
//glReadBuffer(GL_NONE);

// check FBO status
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    return false;

glBindFramebuffer(GL_FRAMEBUFFER, 0);

当我需要画场景的时候

glBindFramebuffer(GL_FRAMEBUFFER, fboMsaaId);
glViewport(0, 0, width, height);
glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

DrawScene();

glBindFramebuffer(GL_READ_FRAMEBUFFER, fboMsaaId);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fboId);
glBlitFramebuffer(0, 0, width, height,  // src rect
    0, 0, width, height,  // dst rect
    GL_COLOR_BUFFER_BIT, // buffer mask
    GL_LINEAR); // scale filter

glBindFramebuffer(GL_FRAMEBUFFER, 0);
glViewport(0, 0, App->window->GetWidth(), App->window->GetHeight());

第二条路：

用MSAA创建FBO

unsigned int framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

// create a multisampled color attachment texture
unsigned int textureColorBufferMultiSampled;
glGenTextures(1, &textureColorBufferMultiSampled);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled);
glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, 4, GL_RGB, SCR_WIDTH, SCR_HEIGHT, GL_TRUE);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, 0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled, 0);

// create a (also multisampled) renderbuffer object for depth and stencil attachments
unsigned int rbo;
glGenRenderbuffers(1, &rbo);
glBindRenderbuffer(GL_RENDERBUFFER, rbo);
glRenderbufferStorageMultisample(GL_RENDERBUFFER, 4, GL_DEPTH24_STENCIL8, SCR_WIDTH, SCR_HEIGHT);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);

if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);

// configure second post-processing framebuffer
unsigned int intermediateFBO;
glGenFramebuffers(1, &intermediateFBO);
glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);

// create a color attachment texture
unsigned int screenTexture;
glGenTextures(1, &screenTexture);
glBindTexture(GL_TEXTURE_2D, screenTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, screenTexture, 0);  // we only need a color buffer

if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    cout << "ERROR::FRAMEBUFFER:: Intermediate framebuffer is not complete!" << endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);

当我需要画出场景时：

 glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
 glViewport(0, 0, width, height);
 glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 DrawScene();

  glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
  glBindFramebuffer(GL_DRAW_FRAMEBUFFER, intermediateFBO);
  glBlitFramebuffer(0, 0, SCR_WIDTH, SCR_HEIGHT, 0, 0, SCR_WIDTH, SCR_HEIGHT, GL_COLOR_BUFFER_BIT, GL_LINEAR);

  glBindFramebuffer(GL_FRAMEBUFFER, 0);
  glViewport(0, 0, App->window->GetWidth(), App->window->GetHeight());

总结：第一种方式:创建FBO，创建颜色RBO和深度RBO，并使用glRenderbufferStorageMultisample(...)指定MSAA级别。然后创建其他FBO与纹理的颜色和RBO的深度。

第二种方法:创建FBO，为颜色创建纹理，为深度创建RBO，在纹理中使用glTexImage2DMultisample(...)作为MSAA级别。然后创建其他FBO和纹理。

使用一种方式和另一种方式有什么不同？一个比另一个好吗？

Answer 1

在您的示例中，MSAA设置实际上在两种情况下都是相同的。您所描述的两种方法之间唯一的区别是--不同的FBO附件类型。通常，当以后需要使用来自FBO的信息进行进一步的呈现时，您将需要附加纹理而不是呈现缓冲区。在这种情况下，您将插入以前的渲染通过FBO的纹理附件到纹理单元，并从它的样本在下一遍着色程序。阴影映射就是其中之一。