Clean up line clipping code in rasterizer

Replace old code with the line clipper from qcosmeticstroker.

Also avoids tripping some issue with the current clang 13 that would
cause paint errors on macOS.

Fixes: QTBUG-98403
Fixes: QTBUG-98388
Pick-to: 6.2 6.2.2
Change-Id: I257eeec6f71153ec51b4176df3be8c443938484c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

1 files changed, 59 insertions, 36 deletions

diff --git a/src/gui/painting/qrasterizer.cpp b/src/gui/painting/qrasterizer.cpp
index 7b26b20db8..5cb4d37eba 100644
--- a/src/gui/painting/qrasterizer.cpp
+++ b/src/gui/painting/qrasterizer.cpp
@@ -744,6 +744,63 @@ static inline QScFixed qSafeFloatToQScFixed(qreal x)
     return QScFixed(tmp);
 }
 
+// returns true if the whole line gets clipped away
+static inline bool qClipLine(QPointF *pt1, QPointF *pt2, const QRectF &clip)
+{
+    qreal &x1 = pt1->rx();
+    qreal &y1 = pt1->ry();
+    qreal &x2 = pt2->rx();
+    qreal &y2 = pt2->ry();
+
+    if (!qIsFinite(x1) || !qIsFinite(y1) || !qIsFinite(x2) || !qIsFinite(y2))
+        return true;
+
+    const qreal xmin = clip.left();
+    const qreal xmax = clip.right();
+    const qreal ymin = clip.top();
+    const qreal ymax = clip.bottom();
+
+    if (x1 < xmin) {
+        if (x2 <= xmin)
+            return true;
+        y1 += (y2 - y1) / (x2 - x1) * (xmin - x1);
+        x1 = xmin;
+    } else if (x1 > xmax) {
+        if (x2 >= xmax)
+            return true;
+        y1 += (y2 - y1) / (x2 - x1) * (xmax - x1);
+        x1 = xmax;
+    }
+    if (x2 < xmin) {
+        y2 += (y2 - y1) / (x2 - x1) * (xmin - x2);
+        x2 = xmin;
+    } else if (x2 > xmax) {
+        y2 += (y2 - y1) / (x2 - x1) * (xmax - x2);
+        x2 = xmax;
+    }
+
+    if (y1 < ymin) {
+        if (y2 <= ymin)
+            return true;
+        x1 += (x2 - x1) / (y2 - y1) * (ymin - y1);
+        y1 = ymin;
+    } else if (y1 > ymax) {
+        if (y2 >= ymax)
+            return true;
+        x1 += (x2 - x1) / (y2 - y1) * (ymax - y1);
+        y1 = ymax;
+    }
+    if (y2 < ymin) {
+        x2 += (x2 - x1) / (y2 - y1) * (ymin - y2);
+        y2 = ymin;
+    } else if (y2 > ymax) {
+        x2 += (x2 - x1) / (y2 - y1) * (ymax - y2);
+        y2 = ymax;
+    }
+
+    return false;
+}
+
 void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width, bool squareCap)
 {
     if (a == b || !(width > 0.0) || d->clipRect.isEmpty())
@@ -760,42 +817,8 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
 
     QPointF offs = QPointF(qAbs(b.y() - a.y()), qAbs(b.x() - a.x())) * width * 0.5;
     const QRectF clip(d->clipRect.topLeft() - offs, d->clipRect.bottomRight() + QPoint(1, 1) + offs);
-
-    if (!clip.contains(pa) || !clip.contains(pb)) {
-        qreal t1 = 0;
-        qreal t2 = 1;
-
-        const qreal o[2] = { pa.x(), pa.y() };
-        const qreal d[2] = { pb.x() - pa.x(), pb.y() - pa.y() };
-
-        const qreal low[2] = { clip.left(), clip.top() };
-        const qreal high[2] = { clip.right(), clip.bottom() };
-
-        for (int i = 0; i < 2; ++i) {
-            if (d[i] == 0) {
-                if (o[i] <= low[i] || o[i] >= high[i])
-                    return;
-                continue;
-            }
-            const qreal d_inv = 1 / d[i];
-            qreal t_low = (low[i] - o[i]) * d_inv;
-            qreal t_high = (high[i] - o[i]) * d_inv;
-            if (t_low > t_high)
-                qSwap(t_low, t_high);
-            if (t1 < t_low)
-                t1 = t_low;
-            if (t2 > t_high)
-                t2 = t_high;
-            if (t1 >= t2)
-                return;
-        }
-
-        QPointF npa = pa + (pb - pa) * t1;
-        QPointF npb = pa + (pb - pa) * t2;
-
-        pa = npa;
-        pb = npb;
-    }
+    if (qClipLine(&pa, &pb, clip))
+        return;
 
     {
         // old delta