Hi, How can I detemine the pixel color of a point on a 3D polygon based only on the texture coordinates and the polygon vertices?

1. You have a 3D point... (I hope Im right)
2. Render the polygon
3. Use glReadPixels to obtain the pixel data
4. Use gluUnProject (or gluProject??? I dont know) to get the position of your point on the screen
5. Get the color from the array returned by glReadPixels...

Hope this helps...



PM

---

Times change.

---

Excuse my poor english!

Opps...

I forgot to mention the reason why I need the pixel color. In essence, I am creating an intersection routine that will allow me to detect the intersection between a line segment and any polygon on my scene. If a hit is detected, I need to determine if the segment actually intersected with a transparent area of the polygon.

For example, assume I have a bush (or tree) in my scene composed of either 1 quad or two triangle. The polygon has a bush texture mapped on it with an alpha channel. There will be areas on the polygon that are transparent. If I hit those areas, I should ignore the intersection.

I need a way to get the alpha component of the texture associated with my 3D intersection point.

I have the following information:

1) The 3D intersection point.
2) The polygon vertices.
3) The texture coordinate associated with each vertices.
4) The polygon normal.
5) The texture size, raster, etc.

I don''t want to render the polygon to get the color. Also, doing it that way would also cause me to loose the alpha channel that I am looking for.

Later, I will use a scoring texture as opposed to a visual texture. The scoring texture will have the same size of the visual texture but it will only be used for intersection. That way I can define solid or hard areas of the object. For example, A ''tree'' can be associated with a single texture although it contain hard and soft surfaces.

I hope this provides for information on what I need.

Opps...

I forgot to mention the reason why I need the pixel color. In essence, I am creating an intersection routine that will allow me to detect the intersection between a line segment and any polygon on my scene. If a hit is detected, I need to determine if the segment actually intersected with a transparent area of the polygon.

For example, assume I have a bush (or tree) in my scene composed of either 1 quad or two triangle. The polygon has a bush texture mapped on it with an alpha channel. There will be areas on the polygon that are transparent. If I hit those areas, I should ignore the intersection.

I need a way to get the alpha component of the texture associated with my 3D intersection point.

I have the following information:

1) The 3D intersection point.
2) The polygon vertices.
3) The texture coordinate associated with each vertices.
4) The polygon normal.
5) The texture size, raster, etc.

I don''t want to render the polygon to get the color. Also, doing it that way would also cause me to loose the alpha channel that I am looking for.

Later, I will use a scoring texture as opposed to a visual texture. The scoring texture will have the same size of the visual texture but it will only be used for intersection. That way I can define solid or hard areas of the object. For example, A ''tree'' can be associated with a single texture although it contain hard and soft surfaces.

I hope this provides for information on what I need.

Interpolation.

You have your hit location of the polygon. Calculate the distance from each vertex, and store it as a percent. Then, use that percent on the texture itself (in memory) and it will give you that current pixel.
Psuedo time:



tada
~Main

==
Colt "MainRoach" McAnlis
Programmer
www.badheat.com/sinewave

Thanks,