Fix: 2D tri/quad vs point intersection tests edge cases #117786

Aras Pranckevicius · 2024-02-03T17:49:43+01:00

2024-02-03 17:49:43 +01:00

isect_point_tri_v2 and isect_point_quad_v2 are handling tris/quads
in either clockwise or counter-clockwise vertex orderings. However,
for counter-clockwise order it was considering points that lie on the edges
or vertices as "inside", whereas for counter-clockwise it was treating
them as "outside", unless they were on the first edge.

Visibly affected place is VSE: it has an optimization that checks
whether a fully opaque strip image fully covers the rendered area.
When the strip was scaled up to exactly cover the rendered area,
the check was failing since isect_point_quad_v2 was saying that a
point is outside the rect.

As far as I can tell, the functions have been "slightly wrong" in
this way for at least 15 years; harder to see through earlier
history in git.

Added a bunch of unit tests to cover this. Without the fix, "edge"
and "corner" cases against "cw" tri/quad were failing.

Performance (checked on clang15 on M1 Max):

isect_point_tri_v2 is pretty much the same performance (assembly
several instructions shorter),
isect_point_quad_v2 is about three times faster (assembly 2x
shorter), seemingly the compiler is able to use some SIMD now.

`isect_point_tri_v2` and `isect_point_quad_v2` are handling tris/quads in either clockwise or counter-clockwise vertex orderings. However, for counter-clockwise order it was considering points that lie on the edges or vertices as "inside", whereas for counter-clockwise it was treating them as "outside", unless they were on the first edge. Visibly affected place is VSE: it has an optimization that checks whether a fully opaque strip image fully covers the rendered area. When the strip was scaled up to *exactly* cover the rendered area, the check was failing since `isect_point_quad_v2` was saying that a point is outside the rect. As far as I can tell, the functions have been "slightly wrong" in this way for at least 15 years; harder to see through earlier history in git. Added a bunch of unit tests to cover this. Without the fix, "edge" and "corner" cases against "cw" tri/quad were failing. Performance (checked on clang15 on M1 Max): - `isect_point_tri_v2` is pretty much the same performance (assembly several instructions shorter), - `isect_point_quad_v2` is about three times *faster* (assembly 2x shorter), seemingly the compiler is able to use some SIMD now.

Aras Pranckevicius added 1 commit 2024-02-03 17:49:53 +01:00

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93886337e8 Fix: 2D tri/quad vs point intersection tests edge cases

isect_point_tri_v2 and isect_point_quad_v2 are handling tris/quads
in either clockwise or counter-clockwise vertex orderings. However,
for clockwise order it was considering points that lie on the edges
or vertices as "inside", whereas for counter-clockwise it was treating
them as "outside".

Visibly affected place is VSE: it has an optimization that checks
whether a fully opaque strip image fully covers the rendered area.
When the strip was scaled up to *exactly* cover the rendered area,
the check was failing since isect_point_quad_v2 was saying that a
point is outside the rect.

As far as I can tell, the functions have been "slightly wrong" in
this way for at least 15 years; harder to see through earlier
history in git.

Added a bunch of unit tests to cover this. Without the fix, "edge"
and "corner" cases against "cw" tri/quad were failing.

Performance (checked on clang15 on M1 Max):
- isect_point_tri_v2 is pretty much the same performance (assembly
  several instructions shorter),
- isect_point_quad_v2 is about three times *faster* (assembly 2x
  shorter), seemingly the compiler is able to use some SIMD now.

Aras Pranckevicius commented

2024-02-03 17:50:10 +01:00

@blender-bot build

Aras Pranckevicius merged commit f6276ec163 into main

2024-02-03 19:03:29 +01:00

Aras Pranckevicius referenced this issue from a commit

2024-02-03 19:03:30 +01:00

Fix: 2D tri/quad vs point intersection tests edge cases

Aras Pranckevicius deleted branch math_isect_point_fix

2024-02-03 19:03:31 +01:00

YimingWu referenced this issue from a commit

2024-02-05 10:56:06 +01:00