Additional tips and tricks for writing GLSL shaders in OGSFX format

When porting pixel shaders from GLSL to OGSFX, in particular shaders found via demo sites, the following tips may be helpful:

See bin\OGSFX in the Maya installation for the Common.ogsfh file.
This file contains common shader code that defines the following uniforms and attributes, which you can re-use in your own shader code:
- world view projection transformation matrix
- screen size
- texture co-ordinates
- vertex shader input structure
- vertex shader output structure
It also includes a default screen quad vertex shader that outputs the position and texture co-ordinates.
NOTE:
Remember to add:
```
#include "Common.ogsfh"
```
Instead of using screen co-ordinates as input in your shader code, use UV co-ordinates. This way, your shader can be applied to any geometry: sphere, plane, and so forth.

For example, instead of using gl_FragCoord.xy, use VSUV (defined in Common.ogsfh).
If you are writing a very simple shader, in lieu of writing your own vertex shader, you can re-use the one defined in Common.ogsfh by specifying it as follows:
```
VertexShader (in VS_INPUT_ScreenQuad, out VS_TO_PS_ScreenQuad) = VS_ScreenQuad;
```
If your shader file fails to load, you can refer to errors in the Maya Output Window.