OpenGL MSAA in 2 different ways. What are the differences? - opengl

Question

I have been looking for OpenGL Multi Sample Anti Aliasing tutorials and I found many but I'll take 2.
They use a different way to do this. I have tested both ways and both work for my project so I can use any of them.
I use this to render my game engine scene to a texture.
This is the 1st way:
Create the FBO with MSAA
// 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);
And when I need to draw the scene
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());
The 2nd way:
Create the FBO with MSAA
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);
And when I need to draw the scene:
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());
Summarizing:
1st way: Create FBO, create RBO for color and RBO for depth and use glRenderbufferStorageMultisample(...) to specify the MSAA level. Then create other FBO with texture for color and RBO for depth.
2nd way: Create FBO, create Texture for color and RBO for depth and using glTexImage2DMultisample(...) for MSAA level in the texture. Then create other FBO and a texture.
What are the differences on using one way or other? Is one better than the other?

Answer 1

MSAA setup in your example is actually the same in both cases. The only difference between the two methods you depicted is - different FBO attachment type. In general, you will want to attach a texture and not render buffer when you later need to use the information from that FBO for further render passes. In such a case you would plug previous render pass FBO's texture attachment into texture unit, and sample from it in the next pass shader program. Shadow mapping is one of such cases.