[gameprogrammer] issues with Calculating texture coordinates

Hi,

I am trying to figure out how to calculate texture coordinates and was looking into some google sites. I also went through Bob's Texture mapping information in gameprogrammer.org page and the PCGPE article. However I still have some doubts :-

Firstly it says to have view space coordinates - I am getting the windows screen coordinates
using the gluProject function OpenGL. Then it says to calculate the P, M, N vectors(i.e. the vertex in the texture space) and then to calculate the 9 magic numbers.

From what I read from the 2 articles - if I have 3 vectors v1, v2 and v3 then

P = v1 ;
M = v2 - P;
N = P - v3;

Now after I calculate the 9 magic numbers and then I calculate the fx and fy(framebuffer vectors) which is the screen space or view space vector v1 -> v1.x / v1.z and v1.y / v1.z.

Using these 9 magic numbers and the frame buffer vector we calculate the values of U and V right and that is the index into the texture to use ?

However this does not seem to work. I have a window coordinate as <320.000000, 240.000000, 0.900901> so if I divide by 0.9 it will give me a value around 355 and in turn the U and V will be a large value.

Is my understanding of view space correct in assuming that its screen coordinates or window coordinates ? And if so then what exactly am I missing.

Also lastly to calculate the UV for each vertex for a triangle the magic numbers needs to be computed once only right and the different fx and fy values give the different UV coordinates ?

Thanks
Gautam




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