From 1896424554498e96f3e3e25999b7b550a1133a05 Mon Sep 17 00:00:00 2001
From: Allan Sandfeld Jensen <allan.jensen@qt.io>
Date: Mon, 30 Sep 2024 14:53:29 +0200
Subject: [PATCH] Fix text drawing onto transparent ARGB32

We can not use the same blend routines for ARGB32 as we use for
ARGB32PM. It needs to blend transparent colors differently.

Pick-to: 6.5
Fixes: QTBUG-91262
Change-Id: I6b75fa8096b92452655dcad94478ae2a74415939
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
(cherry picked from commit bb854606ec8f95787dfd2a4d1b6bcaddbcf4d042)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/gui/painting/qdrawhelper.cpp              |  4 +--
 .../gui/painting/qpainter/tst_qpainter.cpp    | 26 +++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 62032a48690..866745cca69 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -6051,8 +6051,8 @@ DrawHelper qDrawHelper[] =
     {
         blend_color_generic,
         qt_bitmapblit_argb32,
-        qt_alphamapblit_argb32,
-        qt_alphargbblit_argb32,
+        qt_alphamapblit_generic,
+        qt_alphargbblit_generic,
         qt_rectfill_nonpremul_argb32
     },
     // Format_ARGB32_Premultiplied
diff --git a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
index 92b28f65bd0..7528690ae42 100644
--- a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
+++ b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp
@@ -280,6 +280,7 @@ private slots:
 
     void fillPolygon();
 
+    void textOnArgb32();
     void drawImageAtPointF();
     void scaledDashes();
 #if QT_CONFIG(raster_fp)
@@ -5460,6 +5461,31 @@ void tst_QPainter::fillPolygon()
     }
 }
 
+void tst_QPainter::textOnArgb32()
+{
+    QImage backing(100, 20, QImage::Format_RGB32);
+    backing.fill(Qt::white);
+    QImage img(100, 20, QImage::Format_ARGB32);
+    img.fill(Qt::transparent); // Filled with transparent black
+
+    QPainter imagePainter(&img);
+    imagePainter.setPen(Qt::red);
+    imagePainter.setFont(QFontDatabase::systemFont(QFontDatabase::GeneralFont));
+    imagePainter.setRenderHints(QPainter::TextAntialiasing);
+    imagePainter.drawText(img.rect(), Qt::AlignCenter,"Text example");
+    imagePainter.end();
+    imagePainter.begin(&backing);
+    imagePainter.drawImage(backing.rect(), img);
+    imagePainter.end();
+    for (int y = 0; y < backing.height(); ++y) {
+        for (int x = 0; x < backing.width(); ++x) {
+            const uint32_t px = backing.pixel(x, y);
+            // Red over white, should always be full red.
+            QCOMPARE(qRed(px), 255);
+        }
+    }
+}
+
 void tst_QPainter::drawImageAtPointF()
 {
     // Just test we do not crash