Just like any other object in OpenGL we can create a framebuffer object (abbreviated to FBO) by using a function called glGenFramebuffers: First we'll discuss how they actually work and then we'll use them by implementing those cool post-processing effects. The application of framebuffers may not immediately make sense, but rendering your scene to a different framebuffer allows us to use that result to create mirrors in a scene, or do cool post-processing effects for example. By creating our own framebuffer we can get an additional target to render to.

The default framebuffer is created and configured when you create your window (GLFW does this for us). The rendering operations we've done so far were all done on top of the render buffers attached to the default framebuffer. OpenGL gives us the flexibility to define our own framebuffers and thus define our own color (and optionally a depth and stencil) buffer. The combination of these buffers is stored somewhere in GPU memory and is called a framebuffer. So far we've used several types of screen buffers: a color buffer for writing color values, a depth buffer to write and test depth information, and finally a stencil buffer that allows us to discard certain fragments based on some condition. discarding in the fragment shader will produce a lot of needless work and should be avoided whenever a fixed-function test would suffice.Framebuffers Advanced-OpenGL/Framebuffers This is the only way to reap the benefits discussed above. Use the fixed-function test early rather than implementing your own programmable test as part of the shader itself. It has long been a fixed-function test, and for best performance you should keep it that way. You need really modern hardware to sample the stencil buffer from a fragment shader. However, this is where you shot yourself in the foot technically speaking. The more complicated your fragment shader, the more you will benefit from using stencil rejection.ĭraw holes to stencil buffer an then use it in fragment shader to discard landscape fragment The best solution is one that can broadly reject a lot of work.

You add an extra 8-bits of memory per-pixel (pretty much a non-issue on modern hardware) but you can skip the fragment shader stage completely for any fragment that fails the stencil test. That means shader units will not waste time calculating data they are just going to throw out anyway. It can reject large groups of fragments before they make it to the fragment shader stage. Modern hardware performs early stencil testing using the same sort of tile-based approach as early depth.

Opengl es 2.0 stencil buffer