Clean up logical dpi for QImage.

Revert to the pre highdpi-patch behaviour.

Before, both physical and logical DPI would be based
on the dpmx/dpmy variables, which could be changed
with setDotsPerMeter(). The highdpi patch introduced
separate ldpmx/ldpmy variables, which were not
changed by setDotsPerMeter().

This broke when loading images: setDotsPerMeter
would be called but the logical dpi would not change.

Remove ldpmx/ldpmy. Keep scaling the physical dpi
by the devicePixelRatio, which will be set to 1 by
default.

Task-number: QTBUG-29187
Change-Id: I0d6f5f3b8efae5fb1adc0a50b22a5da78324a282
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

3 files changed, 26 insertions, 8 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index de1e555771..975ef54d6b 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -99,8 +99,6 @@ QImageData::QImageData()
       format(QImage::Format_ARGB32), bytes_per_line(0),
       ser_no(qimage_serial_number.fetchAndAddRelaxed(1)),
       detach_no(0),
-      ldpmx(qt_defaultDpiX() * 100 / qreal(2.54)),
-      ldpmy(qt_defaultDpiY() * 100 / qreal(2.54)),
       dpmx(qt_defaultDpiX() * 100 / qreal(2.54)),
       dpmy(qt_defaultDpiY() * 100 / qreal(2.54)),
       offset(0, 0), own_data(true), ro_data(false), has_alpha_clut(false),
@@ -4984,11 +4982,11 @@ int QImage::metric(PaintDeviceMetric metric) const
         return d->depth;
 
     case PdmDpiX:
-        return qRound(d->ldpmx * 0.0254);
+        return qRound(d->dpmx * 0.0254);
         break;
 
     case PdmDpiY:
-        return qRound(d->ldpmy * 0.0254);
+        return qRound(d->dpmy * 0.0254);
         break;
 
     case PdmPhysicalDpiX:
diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index e79eb9d562..18c686e917 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -82,10 +82,8 @@ struct Q_GUI_EXPORT QImageData {        // internal image data
     int ser_no;               // serial number
     int detach_no;
 
-    qreal  ldpmx;               // logical dots per meter X (or 0)
-    qreal  ldpmy;               // logical dots per meter Y (or 0)
-    qreal  dpmx;                // device dots per meter X (or 0)
-    qreal  dpmy;                // device dots per meter Y (or 0)
+    qreal  dpmx;                // dots per meter X (or 0)
+    qreal  dpmy;                // dots per meter Y (or 0)
     QPoint  offset;           // offset in pixels
 
     uint own_data : 1;
diff --git a/tests/auto/gui/image/qimage/tst_qimage.cpp b/tests/auto/gui/image/qimage/tst_qimage.cpp
index 6f372b0160..b668f57909 100644
--- a/tests/auto/gui/image/qimage/tst_qimage.cpp
+++ b/tests/auto/gui/image/qimage/tst_qimage.cpp
@@ -86,6 +86,7 @@ private slots:
 #endif
 
     void dotsPerMeterZero();
+    void dotsPerMeterAndDpi();
 
     void convertToFormatPreserveDotsPrMeter();
     void convertToFormatPreserveText();
@@ -899,6 +900,27 @@ void tst_QImage::dotsPerMeterZero()
 
     QCOMPARE(img.dotsPerMeterX(), defaultDpmX);
     QCOMPARE(img.dotsPerMeterY(), defaultDpmY);
+
+}
+
+// verify that setting dotsPerMeter has an effect on the dpi.
+void tst_QImage::dotsPerMeterAndDpi()
+{
+    QImage img(100, 100, QImage::Format_RGB32);
+    QVERIFY(!img.isNull());
+
+    QPoint defaultLogicalDpi(img.logicalDpiX(), img.logicalDpiY());
+    QPoint defaultPhysicalDpi(img.physicalDpiX(), img.physicalDpiY());
+
+    img.setDotsPerMeterX(100);  // set x
+    QCOMPARE(img.logicalDpiY(), defaultLogicalDpi.y()); // no effect on y
+    QCOMPARE(img.physicalDpiY(), defaultPhysicalDpi.y());
+    QVERIFY(img.logicalDpiX() != defaultLogicalDpi.x()); // x changed
+    QVERIFY(img.physicalDpiX() != defaultPhysicalDpi.x());
+
+    img.setDotsPerMeterY(200);  // set y
+    QVERIFY(img.logicalDpiY() != defaultLogicalDpi.y()); // y changed
+    QVERIFY(img.physicalDpiY() != defaultPhysicalDpi.y());
 }
 
 void tst_QImage::rotate_data()