From 423b6509382c3bcc36eca78ced0254bfb463d017 Mon Sep 17 00:00:00 2001 From: Eirik Aavitsland Date: Fri, 21 Jan 2022 08:05:29 +0100 Subject: Fix painting clipping glitches with fractional scaling In QPainter, clipping can only be done on whole pixels. The various ways of specifying a clipping rectangle to the QPainter API have been inconsistent in how fractional rectangles (either specified directly, or as a result of fractional scaling) are mapped (rounded) to integer coordinates. Also, the mappings have not made sure to keep the edge-to-edge property of clip rects under scaling. This is particularly important when scaling QRegions with multiple rects, as QRegion is designed on the assumption that an area can be described as a set of edge-to-edge rects. The fix rounds a clip rect identically with a fill rect. (Indeed, a followup plan would be to merge QRasterPaintEngine's toNormalizedFillRect() with the rectangle rounding function in this commit). Notably, a QRectF clip is now interpreted the same as a QPainterPath clip describing the same area. This modifies d9cc1499954829faf9486fb72056e29f1bad58e3 Task-number: QTBUG-100329 Fixes: QTBUG-95957 Task-number: QTBUG-100343 Pick-to: 6.3 Change-Id: Iaae6464b9b17f8bf3adc69007f6ef8d623bf2c80 Reviewed-by: Volker Hilsheimer --- src/gui/painting/qmath_p.h | 15 +++++++++++++++ src/gui/painting/qpaintengine_raster.cpp | 6 +++--- src/gui/painting/qtransform.cpp | 6 +++--- 3 files changed, 21 insertions(+), 6 deletions(-) (limited to 'src/gui/painting') diff --git a/src/gui/painting/qmath_p.h b/src/gui/painting/qmath_p.h index 0191f8381f..6691665f41 100644 --- a/src/gui/painting/qmath_p.h +++ b/src/gui/painting/qmath_p.h @@ -53,12 +53,27 @@ #include #include +#include QT_BEGIN_NAMESPACE static const qreal Q_PI = qreal(M_PI); // pi static const qreal Q_MM_PER_INCH = 25.4; +inline QRect qt_mapFillRect(const QRectF &rect, const QTransform &xf) +{ + // Only for xf <= scaling or 90 degree rotations + Q_ASSERT(xf.type() <= QTransform::TxScale + || (xf.type() == QTransform::TxRotate && qFuzzyIsNull(xf.m11()) && qFuzzyIsNull(xf.m22()))); + // Transform the corners instead of the rect to avoid hitting numerical accuracy limit + // when transforming topleft and size separately and adding afterwards, + // as that can sometimes be slightly off around the .5 point, leading to wrong rounding + QPoint pt1 = xf.map(rect.topLeft()).toPoint(); + QPoint pt2 = xf.map(rect.bottomRight()).toPoint(); + // Normalize and adjust for the QRect vs. QRectF bottomright + return QRect::span(pt1, pt2).adjusted(0, 0, -1, -1); +} + QT_END_NAMESPACE #endif // QMATH_P_H diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp index b044b485df..6fbedabdbd 100644 --- a/src/gui/painting/qpaintengine_raster.cpp +++ b/src/gui/painting/qpaintengine_raster.cpp @@ -49,7 +49,7 @@ #include #include #include -#include +#include "qmath_p.h" #include // #include @@ -1195,7 +1195,7 @@ void QRasterPaintEngine::clip(const QVectorPath &path, Qt::ClipOperation op) #endif const qreal *points = path.points(); QRectF r(points[0], points[1], points[4]-points[0], points[5]-points[1]); - if (setClipRectInDeviceCoords(s->matrix.mapRect(r).toAlignedRect(), op)) + if (setClipRectInDeviceCoords(qt_mapFillRect(r, s->matrix), op)) return; } } @@ -1255,7 +1255,7 @@ void QRasterPaintEngine::clip(const QRect &rect, Qt::ClipOperation op) QPaintEngineEx::clip(rect, op); return; - } else if (!setClipRectInDeviceCoords(s->matrix.mapRect(QRectF(rect)).toRect(), op)) { + } else if (!setClipRectInDeviceCoords(qt_mapFillRect(rect, s->matrix), op)) { QPaintEngineEx::clip(rect, op); return; } diff --git a/src/gui/painting/qtransform.cpp b/src/gui/painting/qtransform.cpp index 9d4f28c895..c318958207 100644 --- a/src/gui/painting/qtransform.cpp +++ b/src/gui/painting/qtransform.cpp @@ -45,7 +45,7 @@ #include "qpainterpath.h" #include "qpainterpath_p.h" #include "qvariant.h" -#include +#include "qmath_p.h" #include #include @@ -1486,12 +1486,12 @@ QRegion QTransform::map(const QRegion &r) const QRegion res; if (m11() < 0 || m22() < 0) { for (const QRect &rect : r) - res += mapRect(QRectF(rect)).toRect(); + res += qt_mapFillRect(QRectF(rect), *this); } else { QVarLengthArray rects; rects.reserve(r.rectCount()); for (const QRect &rect : r) { - QRect nr = mapRect(QRectF(rect)).toRect(); + QRect nr = qt_mapFillRect(QRectF(rect), *this); if (!nr.isEmpty()) rects.append(nr); } -- cgit v1.2.3