[Algorithms] Texel area

[Diogo de A. <dio...@sp...>]

Hi all!

 

I've been struggling with a problem and I hope somebody can point me in the
right direction...

I'm making a lightmap/ambient occlusion map generator system, and for that I
built a rasterizer that calls a function that does the computations and
fills the target image.

The rasterizer works in UV space, but all parameters of the triangle are
interpolated.

 

Now, I wanted to add multisampling, so that I don't get just a single sample
for the ambient occlusion, and I want to "jitter" the source point (not only
the raycast direction), 

and for that I need to find out what's the area of the target lumel. By
area, I mean not only the actual area value, but the "rectangle" that bounds
the lumel, in world space...

 

So, what I want to do is, given 

 

- triangle T=(V1,V2,V3), in which V1, V2, V3 are vertexes that have some
properties (world space position, normal, diffuse color, texture coordinates
0 (in uniform space), texture coordinates 1 (in texture space, [0..texture
size[), etc),

- texture size

- position inside the triangle (absolute value in texture space)

 

is to find out the rectangle that bounds the texel in world space (origin+2
vectors)...

 

I've been thinking about this, but can't seem to find an approach that works
correctly... I'm expecting some error in this calculation (due to the
rasterizing process itself), but it's not a big deal since it's for sampling
purposes, but even so I can't seem to make it work...

 

So, if anyone got any links, keywords, or just a simple algorithm he doesn't
mind sharing, I'd appreciate it!

 

Best regards,

Diogo de Andrade