Master's Thesis - Studierstube Augmented Reality Project - Graz ...

4.4 Visualization Framework
The order is arbitrary and recurrences are allowed. (for example vector.xxwy).
{s,t,p,q}-letters are allowed for indexing as well.
• All basic matrix and vector operations are available for the according types.
• Many standard geometric, trigonometric and exponential functions are available
as described in [Fernandes2007]
built-in variables, attributes and constants
The most important of them are listed below. A complete list of them is given in
[Tatarchuk2004]
• vertex shader writable variables
– vec4 gl_Position: equals to the homogeneous coordinate position of the
vertex and must be written.
• vertex shader readable attributes:
– vec4 gl_Color: color value of the vertex;
– vec4 gl_Normal: normal vector of the vertex;
– vec4 gl_Vertex: coordinate of the vertex;
– vec4 gl_MultiTexCoord0..7: texture coordinates on texture units 0...7.
• fragment shader writable variables:
– vec4 gl_FragColor: must be written and defines the color of the output
fragment;
– vec4 gl_FragData[0..15]: refers to the same as vec4 gl_FragColor but
for multiple render targets.
• fragment shader readable attributes:
– vec4 gl_FragCoord: reads the position of the fragment relative to the window
position (x,y,z,1/w);
– bool gl_FrontFacing: reads if the fragment belongs to a front facing primitive.
76