High-dpi drawTiledPixmap (raster paint engine)

Implement more consistent behavior for drawTiledPixmap(),
which should produce the same visual tiling pattern
independent of display devicePixelRatio

Consider the following pixmaps and draw calls:

  QPixmap px32; // 32x32
  QPixmap px64; // 64x64
  drawTiledPixmap(QRect(0, 0, 128, 128), px32);
  drawTiledPixmap(QRect(0, 0, 128, 128), px64);

On 1x displays this will produce 4x4 and 2x2 tiles,
respectively.

On 2x displays this would previously produce a different
tiling pattern, where the paint engine would tile in
the device pixel coordinate system. Change this to
tile in the device independent coordinate system,
producing the same visual tiling pattern as the 1x case.

It is possible to produce a 4x4 tiling pattern with
high-resolution output from the 64x64 pixmap by setting
the devicePixelRatio:

  QPixmap px64;
  px64.setDevicePixelRatio(2);
  drawTiledPixmap(QRect(0, 0, 128, 128), px64);

This change adds an inverse scale to the image filler
transform that accounts for the pixmap devicePixelRatio.

[ChangeLog][QtGui] QPainter::drawTiledPixmap() now
tiles in the device independent coordinate system.

Change-Id: I4918d274192967f222f181b374571c7c597dcd76
Reviewed-by: Jonathan Courtois <jonathan.courtois@gmail.com>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: 石博文 <sbw@sbw.so>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 54 insertions, 0 deletions

diff --git a/tests/manual/highdpi/main.cpp b/tests/manual/highdpi/main.cpp
index bd6af75b16..6f854a68d4 100644
--- a/tests/manual/highdpi/main.cpp
+++ b/tests/manual/highdpi/main.cpp
@@ -334,6 +334,59 @@ void PixmapPainter::paintEvent(QPaintEvent *)
     x+=dx * 2; p.drawImage(QRect(x, y, pixmapPointSize * 2, pixmapPointSize * 2), imageLarge);
  }
 
+class TiledPixmapPainter : public QWidget
+{
+public:
+    QPixmap pixmap1X;
+    QPixmap pixmap2X;
+    QPixmap pixmapLarge;
+
+    TiledPixmapPainter();
+    void paintEvent(QPaintEvent *event);
+};
+
+TiledPixmapPainter::TiledPixmapPainter()
+{
+    pixmap1X = QPixmap(":/qticon32.png");
+    pixmap2X = QPixmap(":/qticon32@2x.png");
+    pixmapLarge = QPixmap(":/qticon64.png");
+}
+
+void TiledPixmapPainter::paintEvent(QPaintEvent *event)
+{
+    QPainter p(this);
+
+    int xoff = 10;
+    int yoff = 10;
+    int tiles = 4;
+    int pixmapEdge = 32;
+    int tileAreaEdge = pixmapEdge * tiles;
+
+    // Expected behavior for both 1x and 2x dislays:
+    // 1x pixmap   : 4 x 4 tiles
+    // large pixmap: 2 x 2 tiles
+    // 2x pixmap   : 4 x 4 tiles
+    //
+    // On a 2x display the 2x pimxap tiles
+    // will be drawn in high resolution.
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmap1X);
+    yoff += tiles * pixmapEdge + 10;
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmapLarge);
+    yoff += tiles * pixmapEdge + 10;
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmap2X);
+
+    // Again, with an offset. The offset is in
+    // device-independent pixels.
+    QPoint offset(40, 40); // larger than the pixmap edge size to exercise that code path
+    yoff = 10;
+    xoff = 20 + tiles * pixmapEdge ;
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmap1X, offset);
+    yoff += tiles * pixmapEdge + 10;
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmapLarge, offset);
+    yoff += tiles * pixmapEdge + 10;
+    p.drawTiledPixmap(QRect(xoff, yoff, tileAreaEdge, tileAreaEdge), pixmap2X, offset);
+}
+
 class Labels : public QWidget
 {
 public:
@@ -1119,6 +1172,7 @@ int main(int argc, char **argv)
 
     DemoContainerList demoList;
     demoList << new DemoContainer<PixmapPainter>("pixmap", "Test pixmap painter");
+    demoList << new DemoContainer<TiledPixmapPainter>("tiledpixmap", "Test tiled pixmap painter");
     demoList << new DemoContainer<Labels>("label", "Test Labels");
     demoList << new DemoContainer<MainWindow>("mainwindow", "Test QMainWindow");
     demoList << new DemoContainer<StandardIcons>("standard-icons", "Test standard icons");