I'm doing ray casting in the fragment shader. I can think of a couple ways to draw a fullscreen quad for this purpose. Either draw a quad in clip space with the projection matrix set to the identity matrix, or use the geometry shader to turn a point into a triangle strip. The former uses immediate mode, deprecated in OpenGL 3.2. The latter I use out of novelty, but it still uses immediate mode to draw a point.
What’s the best way to draw a fullscreen quad in OpenGL 3.2
glslopengl
Best Answer
You can send two triangles creating a quad, with their vertex attributes set to -1/1 respectively.
You do not need to multiply them with any matrix in the vertex/fragment shader.
Here are some code samples, simple as it is :)
Vertex Shader:
Fragment Shader :