Visibility checking

Yeah I want one too. That''s why I have been doing RESEARCH and am going to WRITE MY OWN algorithm... Seriously, people don''t just dish out their code. Plus, it''s a complicated topic.

3 Letters BSP. Check out the tutorial at www.grandus.com

If you want a solid tree. Check out the D3D tutorial at www.mrgamemaker.com

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I wrote the best video game ever, then I woke up...

BSP? That''s a little overkill if it''s not meant to be realtime.

What you need to do is calculate a vector from the camera position to any vertex on the polygon. Then calculate the Dot Product of this vector with the surface normal of the polygon. The polygon is facing the viewer if the result is negative.

for one triangle?

as above for the backfaced culling also

prolly the quickest way (it''ll give u all the triangles but might give some that arent actually in the view frustum)
take the point (A) in the center of the triangle. find the distance(B) to its most distant vertice.
measure the distance from the A to each of the viewfrustum planes if the distance is less than B then draw the triangle.

its also possible to do an accurate check tri with plane but it requires quite a bit more maths and will be quite a bit slower. though u could do this test for any tris that are borderline on the above test.

http://members.xoom.com/myBollux

Thanks for the help. But I need to make sure that the triangle also isn''t blocked by other triangles. Also, I don''t really have a view frustrum because I want to know if the triangle is visible from any camera orientation.

I think what I''ll do is render 6 shots from the camera, each shot orthagonal to each other. The triangle I want to check will be blue, and all the other triangles will be red. Then I''ll just scan for a blue pixel in all of the shots. If I find one, then
the triangle is visible, if I don''t then it''s not.

The only problem is I need to know if the triangle is visible from anywhere in a box. I guess I could just try 20 different positions inside the box.

I need this so I can make the scene render quicker. Like if I''m at a certain point, I KNOW exactly which triangles are visible and which aren''t so I don''t even have to pass them to the renderer.

It sounds like you are trying to compute PVS (potentialy visible set). A web search will turn up lots of information on PVS, or check the BSP/PVS tutorial on www.mr-gamemaker.com as it does exactly what I think you are after.

Alan