Introduction to the Terrain Renderer

The title for my honours project is "GPU Based Algorithms for Terrain Texturing". My goal is to find interesting and useful texturing algorithms using graphics hardware, specifically for 3D terrain.

To help me with this my supervisor, Mukundan, gave me code for a Terrain Renderer using ROAM (as far as I know this was written by a previous honours student). This meant I could focus on the texturing and GPU side of things, rather than the geometry. The majority of the current system was not written by me. In fact I have initially only added 2 classes.

Terrain Rendering

todo

Shaders

Shaders are basically pieces of code that run on graphics hardware. There are three types of shaders; geometry, vertex and fragment/pixel shaders. I only use vertex and fragment shaders (geometry shaders are pretty new). Vertex shaders are called for every vertex that is drawn, so they are generally responsible for transforming vertices, generating texture coordinates and possibly lighting. Fragment shaders are called for every pixel (or multiple times per pixel, hence the term fragment) that is drawn. They are responsible for setting the colour at every point, so generally they will use textures and lighting and combine them in the way you want.

By nature shaders are very hardware dependant. Not so much as assembly code, but some functionality is only available on some hardware. For example, it's only fairly recently (last 2 or 3 years) that shaders have supported dynamic branching (if then else) and even now, some hardware implements it in a way that you would not expect that can result in slow performance unexpectedly.

To get a shader to do something reasonably interesting, you need a way to pass information to it. This can be done either with textures, or with uniform variables. A uniform variable is set from your main code using an OpenGL function (unless you're using DirectX of course, but that's not me). To do this, you need to know the name of the variable defined in the shader, so this means your main code is coupled to the shader. Which sort of makes sense if they need to cooperate to provide a particular effect.

In terms of my design, I should try to abstract away from the shaders as much as possible, but there is always going to be some degree of coupling there.

Initial Design

todo