processing / processing/processing4

PShape.contains() is broken for transformed shapes (double invert)

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Description

contains() in PShape is inverting the matrix twice, so it cancels itself out and hit-testing runs in the wrong space.

In PShape.java:

PMatrix inverseCoords = matrix.get();
inverseCoords.invert();
inverseCoords.invert();
inverseCoords.mult(new PVector(x, y), p);

That second invert() should not be there.

So for translated/rotated/scaled shapes, contains(x, y) gives wrong answers.

Quick repro:

PShape s = createShape(RECT, 0, 0, 50, 50);
s.translate(100, 100);
println(s.contains(120, 120)); // false, should be true

Expected: point-in-shape test respects the shape transform.
Actual: transform handling is wrong because inverse matrix is never actually applied.

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start in PShape.java at contains(), where the issue identifies two consecutive matrix inversions. Run the supplied translated-rectangle repro and verify that removing the extra inversion makes contains(120, 120) return true for the transformed shape.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
computer-graphics
Issue type
Bug
Difficulty
1/5
Estimated time
Under an hour
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
55/100

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