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Assert that custom painters balance save/restores.

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This commit is contained in:
Hixie 2016-02-11 17:06:07 -08:00
parent 16ecfeb074
commit 0d1a3cfcff
2 changed files with 36 additions and 2 deletions
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36
packages/flutter/lib/src/rendering/proxy_box.dart
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@ -1264,9 +1264,43 @@ class RenderCustomPaint extends RenderProxyBox {
} }
void _paintWithPainter(Canvas canvas, Offset offset, CustomPainter painter) { void _paintWithPainter(Canvas canvas, Offset offset, CustomPainter painter) {
int debugPreviousCanvasSaveCount;
canvas.save();
assert(() { debugPreviousCanvasSaveCount = canvas.getSaveCount(); return true; });
canvas.translate(offset.dx, offset.dy); canvas.translate(offset.dx, offset.dy);
painter.paint(canvas, size); painter.paint(canvas, size);
canvas.translate(-offset.dx, -offset.dy); assert(() {
// This isn't perfect. For example, we can't catch the case of
// someone first restoring, then setting a transform or whatnot,
// then saving.
// If this becomes a real problem, we could add logic to the
// Canvas class to lock the canvas at a particular save count
// such that restore() fails if it would take the lock count
// below that number.
int debugNewCanvasSaveCount = canvas.getSaveCount();
if (debugNewCanvasSaveCount > debugPreviousCanvasSaveCount) {
throw new RenderingError(
'The $painter custom painter called canvas.save() or canvas.saveLayer() at least '
'${debugNewCanvasSaveCount - debugPreviousCanvasSaveCount} more '
'time${debugNewCanvasSaveCount - debugPreviousCanvasSaveCount == 1 ? '' : 's' } '
'than it called canvas.restore().\n'
'This leaves the canvas in an inconsistent state and will probably result in a broken display.\n'
'You must pair each call to save()/saveLayer() with a later matching call to restore().'
);
}
if (debugNewCanvasSaveCount < debugPreviousCanvasSaveCount) {
throw new RenderingError(
'The $painter custom painter called canvas.restore() '
'${debugPreviousCanvasSaveCount - debugNewCanvasSaveCount} more '
'time${debugPreviousCanvasSaveCount - debugNewCanvasSaveCount == 1 ? '' : 's' } '
'than it called canvas.save() or canvas.saveLayer().\n'
'This leaves the canvas in an inconsistent state and will result in a broken display.\n'
'You should only call restore() if you first called save() or saveLayer().'
);
}
return debugNewCanvasSaveCount == debugPreviousCanvasSaveCount;
});
canvas.restore();
} }
void paint(PaintingContext context, Offset offset) { void paint(PaintingContext context, Offset offset) {

2
packages/flutter/lib/src/widgets/checked_mode_banner.dart
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@ -15,7 +15,7 @@ class _CheckedModeBannerPainter extends CustomPainter {
static const kHeight = 12.0; // height of banner static const kHeight = 12.0; // height of banner
static const kTextAlign = const Offset(0.0, -3.0); // offset to move text up static const kTextAlign = const Offset(0.0, -3.0); // offset to move text up
static const kFontSize = kHeight * 0.85; static const kFontSize = kHeight * 0.85;
static const kShadowBlur = 8.0; // shadow blur sigma static const kShadowBlur = 4.0; // shadow blur sigma
static final Rect kRect = new Rect.fromLTWH(-kOffset, kOffset-kHeight, kOffset * 2.0, kHeight); static final Rect kRect = new Rect.fromLTWH(-kOffset, kOffset-kHeight, kOffset * 2.0, kHeight);
static const TextStyle kTextStyles = const TextStyle( static const TextStyle kTextStyles = const TextStyle(
color: const Color(0xFFFFFFFF), color: const Color(0xFFFFFFFF),