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renderer: properly support stroke bounding box after scaling.

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The stroke bounding box in ThorVG was previously only approximated,
as the stroke transformation was mistakenly omitted. This has now
been enhanced.

The stroke join/corner is still not taken into account in the
bounding box computation...
This commit is contained in:
Hermet Park 2025-07-24 18:16:31 +09:00 • committed by Hermet Park
parent 0cb903c711
commit 7730f8ba8b
2 changed files with 11 additions and 5 deletions
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3
examples/BoundingBox.cpp
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@ -256,10 +256,11 @@ struct UserExample : tvgexam::Example
shape->moveTo(0, 0);
shape->lineTo(150, 100);
shape->lineTo(0, 100);
shape->close();
shape->fill(255, 0, 255);
shape->strokeWidth(30);
shape->strokeFill(0, 255, 255);
shape->close();
shape->strokeJoin(tvg::StrokeJoin::Round);
tvg::Matrix m = {1.8794f, -0.6840f, 0.0f, 0.6840f, 1.8794f, 0.0f, 0.0f, 0.0f, 1.0f};
shape->transform(m);

13
src/renderer/tvgShape.h
View file

@ -125,10 +125,15 @@ struct ShapeImpl : Shape
//Stroke feathering
if (stroking && rs.stroke) {
x -= rs.stroke->width * 0.5f;
y -= rs.stroke->width * 0.5f;
w += rs.stroke->width;
h += rs.stroke->width;
//Use geometric mean for feathering.
//Join, Cap wouldn't be considered. Generate stroke outline and compute bbox for accurate size?
auto sx = sqrt(m.e11 * m.e11 + m.e21 * m.e21);
auto sy = sqrt(m.e12 * m.e12 + m.e22 * m.e22);
auto feather = rs.stroke->width * sqrt(sx * sy);
x -= feather * 0.5f;
y -= feather * 0.5f;
w += feather;
h += feather;
}
pt4[0] = {x, y};