Shader-coding: nonlinear projection models

Question

As I understand it, the standard projection model places an imaginary grid in front of the camera, and for each triangle in the scene, determines which 3 pixels its 3 corners project onto. The color is determined for each of these points, and the fragment shader fills in the rest using interpolation.

My question is this: is it possible to gain control over this projection model? For example, create my own custom distorted uv-grid? Or even just supply my own algorithm:

xyPixelPos_for_Vector3( Vector3 v ) {...}

I'm working in Unity3D, so I think that limits me to cG or openGL.

I did once write a GLES2 shader, but I don't remember ever performing any kind of "ray hits quad" type test to resolve the pixel position of a particular 3D point in space.

Answer 1

I'm going to assume that you want to render 3d images based upon 3d primitives that are defined by vertices. This is not the only way to render images with OpenGL but it is the most common. The technique that you describe sounds much more like Ray-Tracing.

How OpenGL Typically Works:

I wouldn't say that OpenGL creates an imaginary grid. Instead, what it does is take the positions of each of your vertices, and converts them into a different space using linear algebra (Matrices).

If you want to start playing around with this, it would be best to do some reading on Matrices, to understand what the graphics card is doing.

You can easily start warping the positions of Vertices by making a vertex shader. However, there is some setup involved. See the Lighthouse tutorials (http://www.lighthouse3d.com/tutorials/glsl-tutorial/hello-world-in-glsl/) to get started with that! You will also want to read their tutorials on lighting (http://www.lighthouse3d.com/tutorials/glsl-tutorial/lighting/), to create a fully functioning vertex shader which includes a lighting model.

Thankfully, once the shader is set up, you can distort your entire scene to your hearts content. Just remember to do your distortions in the right 'space'. World coordinates are much different than eye coordinates!