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isPointInTriangle returning true when it shouldn't

See original GitHub issue

Issue details

Intersector#isPointInTriangle fails for points lying on the plane of the triangle but not within it due to a floating-point rounding error in some cases.

The last check if the function:

if (ab * bc - ac * bb < 0) return false;

is sometimes having its arithmetic being rounded to 0.0 causing the function to return true even though the answer should be false.

Reproduction steps/code

Intersector.isPointInTriangle(
                new Vector3( -5120.8345f,8946.126f,-3270.5813f),

                new Vector3(50.008057f, 22.20586f, 124.62208f),

                new Vector3( 62.282288f, 22.205864f, 109.665924f),

                new Vector3(70.92052f, 7.205861f, 115.437805f))

will return true even though the point is clearly not in the triangle.

Version of libGDX and/or relevant dependencies

Tested on version 1.10.0 however should still be failing on all versions

Issue Analytics

State:
Created a year ago
Comments:5 (2 by maintainers)

Top GitHub Comments

1reaction

tylerhasmancommented, Jun 16, 2022

Looks like this new function that @tommyettinger created is working well. I’ll try to remember and create a pull request tonight

0reactions

tommyettingercommented, Jun 17, 2022

Hooray for numeric stability!

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