On Thursday, 30 March 2023 at 12:59:31 UTC, Dennis wrote:
On Thursday, 30 March 2023 at 10:29:25 UTC, z wrote:
Is this code correct or logically sound?
You need to be exact on what 'correct' is. The comment above
`triangleFacesCamera` says:
Indicates wether a triangle faces an imaginary view point.
There's no view point / camera position defined anywhere in
your code.
Instead, all it's doing is comparing the angle of one triangle
side (A->B) with another (B->C) in the XZ plane. This suggests
you want to know the triangle winding order: clockwise or
counter clockwise.
If you search for "triangle winding order" you'll find simple
and correct ways to do that. Your code needlessly computes
angles, only considers the XZ plane, and doesn't compare the
angles correctly.
r2 -= r1;
return r2 > 0;
You need to wrap (r2 - r1) into [-τ/2, τ/2] range, then you can
compare with 0.
Yes, the viewpoint/cam should be [0,0,0] for now. The old
algorithm completely discards depth information after scaling
triangle point data depending on depth distance from 0 hence why
i ignored it.
I've tried to search before but was only able to find articles
for 3D triangles, and documentation for OpenGL, which i don't use.
My description of the old algorithm was also badly written(it is
confusing!) so here it is rewritten to be more understandable :
```D
enum {x, y}//leftright/side, updown/height
alias tri = byte[2];
/**
Determines if a triangle is visible.
*/
extern bool oldfunction(tri tA, tri tB, tri tC) {
short r0, r1;//r, "result"
r0 = cast(short) ((tB[y]-tA[y]) * (tC[x]-tB[x]));
r1 = cast(short) ((tC[y]-tA[y]) * (tB[x]-tA[x]));
r1 -= r0;
return r1 > 0;//"visible" means result is neither negative or zero
}
```
(replacing my code with this but in float point "works" but there
is an apparent "angle bias" and other problems that are difficult
to pinpoint or describe.)
Does this match anything known? It doesn't look like cross
product to me because the subtractions occur earlier than the
multiplications.
By correct i mean that it can be used exactly like the old
algorithm. (to ignore subshapes from a 3D model)
Thanks again