Hi

I am currently reading a paper by Cass Everitt on shadow mapping and I have one question. In the paper, there is an equation for calculating the texture coordinates like so:

[s, t, r, q] = S P L M[xo, yo, zo, wo]

s, t, r, q are the texture coords

xo, yo, zo, wo are the coords given in object space

M is the matrix that transforms from object to world space

L transforms from world to light space

P is the projection matrix for the light source

S is the scale-bias matrix, but what exactly does it do? It is given as

|0.5 0.0 0.0 0.5|

|0.0 0.5 0.0 0.5|

|0.0 0.0 0.5 0.5|

|0.0 0.0 0.0 1.0|

So the question is what is S, the scale-bias matrix? What does it do, and why does it have to be specified as such?

Regards