Re: Is this code correct?
On Saturday, 1 April 2023 at 15:32:27 UTC, Dennis wrote: On Friday, 31 March 2023 at 13:11:58 UTC, z wrote: 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. The first function you posted takes a 3D triangle as input, so I assumed you're working in 3D. What are you working on? Determines if a triangle is visible. You haven't defined what 'visible' means for a geometric triangle. explained to the best of my ability : https://d.godbolt.org/z/4a8zPGsGo the "angle bias" i was trying to explain about is present, when `rot = 0` the `mask` is supposed to only have three `true` values.(that of the "front" triangle.) You haven't defined what 'visible' means for a geometric triangle. Problem is, all i have is an assembly dump and the data it interacts with, both of which are very(very) old.
Re: Is this code correct?
On Friday, 31 March 2023 at 13:11:58 UTC, z wrote: 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. The first function you posted takes a 3D triangle as input, so I assumed you're working in 3D. What are you working on? Determines if a triangle is visible. You haven't defined what 'visible' means for a geometric triangle.
Re: Is this code correct?
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
Re: Is this code correct?
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.
Is this code correct?
Is this code correct or logically sound?
```D
import std;
enum {side/depth/height and side/height
x,//0
y,//1
z //2
}
/**
Indicates wether a triangle faces an imaginary view point.
*/
bool triangleFacesCamera(float[3] tA, float[3] tB, float[3] tC) {
float r1, r2;
r1 = atan2(tB[x] - tA[x], tB[z] - tA[z]);//tried swapping
parameters without success
r2 = atan2(tC[x] - tB[x], tC[z] - tB[z]);//also tried with tA as
substraction 2nd operand, with same/similar results.
//trying with both is still broken, but appears to change the
breakage pattern.
r2 -= r1;
return r2 > 0;
}
```
For context, it is trying to reproduce an old algorithm that does
the same thing :
```D
//in D pseudo code
extern short sus(byte A, byte B){
r0 = sus(tB[y] - tA[y], tB[x] - tA[x]);
r1 = sus(tC[y] - tA[y], tC[x] - tA[x]);
r1 -= r0;
return r1 > 0;
}
```
`sus` is named so because it makes use of `atan` and a premade
table that *looks like* `tan(a*(a*5.09...))` but is impossible to
exactly reproduce for me.(on a graph it looks like tan but
crammed to loop only four/sixteen/sixtyfour times at τ/4,π,τ)
Trying to parse both `atan2` and `sus` with `(sin(angle),
cos(angle))` as arguments[1] shows that atan2 outputs it as an
angle in `-π~π` angle representation but `sus`'s output differs
in that it looks like `sin(x*2)`.
I'd add images to better illustrate it but do not know how...
Big thanks
[1] https://run.dlang.io/is/xR8TcE
ps: is it normal that sometimes posting has a very long delay?
when it happens it is as if the post has gone nowhere but then it
suddenly appears much later, which can cause confusion and
duplicate posting, oof.
