Improve rounding in QCosmeticStroker

Fixes the drawn position of end points in drawLine.

Based on a patch by Jørgen Lind, and modified so that
it caused no test regressions.

Task-number: QTBUG-38144
Change-Id: I24aa28480cc6ae09abf91d80378970565a29b254
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 45 insertions, 0 deletions

diff --git a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
index 159bb6a041..f6167262a9 100644
--- a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
+++ b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
@@ -111,6 +111,7 @@ private slots:
     void drawLine_task190634();
     void drawLine_task229459();
     void drawLine_task234891();
+    void drawLineEndPoints();
 
     void drawRect_data() { fillData(); }
     void drawRect();
@@ -1036,6 +1037,50 @@ void tst_QPainter::drawLine_task216948()
         QCOMPARE(img.pixel(0, i), QColor(Qt::black).rgba());
 }
 
+void tst_QPainter::drawLineEndPoints()
+{
+    QImage img(256, 256, QImage::Format_ARGB32_Premultiplied);
+    img.fill(0x0);
+
+    QPainter p;
+    for (int x = 0; x < img.width(); ++x) {
+        QRgb color = qRgb(x, 0, 0);
+        p.begin(&img);
+        p.setPen(QPen(color));
+        p.drawLine(x, 0, 255 - x, 255);
+        p.end();
+        QCOMPARE(img.pixel(x, 0), color);
+        QCOMPARE(img.pixel(255 - x, 255), color);
+    }
+    for (int y = 0; y < img.height(); ++y) {
+        QRgb color = qRgb(0, y, 0);
+        p.begin(&img);
+        p.setPen(QPen(color));
+        p.drawLine(0, y, 255, 255 - y);
+        p.end();
+        QCOMPARE(img.pixel(0, y), color);
+        QCOMPARE(img.pixel(255, 255 - y), color);
+    }
+    for (int x = 0; x < img.width(); ++x) {
+        QRgb color = qRgb(x, 0, x);
+        p.begin(&img);
+        p.setPen(QPen(color));
+        p.drawLine(x, 255, 255 - x, 0);
+        p.end();
+        QCOMPARE(img.pixel(x, 255), color);
+        QCOMPARE(img.pixel(255 - x, 0), color);
+    }
+    for (int y = 0; y < img.height(); ++y) {
+        QRgb color = qRgb(0, y, y);
+        p.begin(&img);
+        p.setPen(QPen(color));
+        p.drawLine(255, y, 0, 255 - y);
+        p.end();
+        QCOMPARE(img.pixel(255, y), color);
+        QCOMPARE(img.pixel(0, 255 - y), color);
+    }
+}
+
 void tst_QPainter::drawRect()
 {
     QFETCH(QRect, rect);