Fixed QPainter::begin() so that it fails gracefully.

Fixed QPainter::begin() so that if it fails, it can still be used on
other paint devices without causing an assert. Autotest included.
I also made begin() fail on images with the QImage::Format_Indexed8
format and added warnings in the documentation since painting on such
images is not supported.

Reviewed-by: Trond

1 files changed, 40 insertions, 0 deletions

diff --git a/tests/auto/qpainter/tst_qpainter.cpp b/tests/auto/qpainter/tst_qpainter.cpp
index 9515d87..2231287 100644
--- a/tests/auto/qpainter/tst_qpainter.cpp
+++ b/tests/auto/qpainter/tst_qpainter.cpp
@@ -238,6 +238,8 @@ private slots:
 
     void taskQT4444_dontOverflowDashOffset();
 
+    void painterBegin();
+
 private:
     void fillData();
     QColor baseColor( int k, int intensity=255 );
@@ -4312,5 +4314,43 @@ void tst_QPainter::taskQT4444_dontOverflowDashOffset()
     QVERIFY(true); // Don't crash
 }
 
+void tst_QPainter::painterBegin()
+{
+    QImage nullImage;
+    QImage indexed8Image(16, 16, QImage::Format_Indexed8);
+    QImage rgb32Image(16, 16, QImage::Format_RGB32);
+    QImage argb32Image(16, 16, QImage::Format_ARGB32_Premultiplied);
+
+    QPainter p;
+
+    // Painting on null image should fail.
+    QVERIFY(!p.begin(&nullImage));
+
+    // Check that the painter is not messed up by using it on another image.
+    QVERIFY(p.begin(&rgb32Image));
+    QVERIFY(p.end());
+
+    // If painting on indexed8 image fails, the painter state should still be OK.
+    if (p.begin(&indexed8Image))
+        QVERIFY(p.end());
+    QVERIFY(p.begin(&rgb32Image));
+    QVERIFY(p.end());
+
+    // Try opening a painter on the two different images.
+    QVERIFY(p.begin(&rgb32Image));
+    QVERIFY(!p.begin(&argb32Image));
+    QVERIFY(p.end());
+
+    // Try opening two painters on the same image.
+    QVERIFY(p.begin(&rgb32Image));
+    QPainter q;
+    QVERIFY(!q.begin(&rgb32Image));
+    QVERIFY(!q.end());
+    QVERIFY(p.end());
+
+    // Try ending an inactive painter.
+    QVERIFY(!p.end());
+}
+
 QTEST_MAIN(tst_QPainter)
 #include "tst_qpainter.moc"