WIP: Add PdmDevicePixelRatioScaled.

Work around QPainDevice::metric's int return type
by adding a new metric that returns a scaled devicePixelRatio.
Choose a scale factor that gives us more than enough
range.

The QPainDevice::devicePixelRatio() convenience accessor
is public API and can unfortunately not be changed
to return a qreal. Add devicePixelRatioF() which
returns the (unscaled) devicePixelRatio.

Change all call sites of QPainDevice::devicePixelRatio()
to use QPainDevice::devicePixelRatioF().

Task-number: QTBUG-38858
Change-Id: Ia97c24e1c7b10241d6425fab2fa513702bb750b8

12 files changed, 37 insertions, 9 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index 5cc1cf760f..57c290492c 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -3782,6 +3782,10 @@ int QImage::metric(PaintDeviceMetric metric) const
         return d->devicePixelRatio;
         break;
 
+    case PdmDevicePixelRatioScaled:
+        return d->devicePixelRatio * QPaintDevice::devicePixelRatioFScale;
+        break;
+
     default:
         qWarning("QImage::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/image/qpixmap_blitter.cpp b/src/gui/image/qpixmap_blitter.cpp
index f24cbc3db9..92f87b6ea9 100644
--- a/src/gui/image/qpixmap_blitter.cpp
+++ b/src/gui/image/qpixmap_blitter.cpp
@@ -115,6 +115,8 @@ int QBlittablePlatformPixmap::metric(QPaintDevice::PaintDeviceMetric metric) con
         return qt_defaultDpiY();
     case QPaintDevice::PdmDevicePixelRatio:
         return devicePixelRatio();
+    case QPaintDevice::PdmDevicePixelRatioScaled:
+        return devicePixelRatio() * QPaintDevice::devicePixelRatioFScale;
     default:
         qWarning("QRasterPlatformPixmap::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/image/qpixmap_raster.cpp b/src/gui/image/qpixmap_raster.cpp
index 9c8835a7a0..6d4e90a6c4 100644
--- a/src/gui/image/qpixmap_raster.cpp
+++ b/src/gui/image/qpixmap_raster.cpp
@@ -288,6 +288,9 @@ int QRasterPlatformPixmap::metric(QPaintDevice::PaintDeviceMetric metric) const
         return qt_defaultDpiY();
     case QPaintDevice::PdmDevicePixelRatio:
         return image.devicePixelRatio();
+    case QPaintDevice::PdmDevicePixelRatioScaled:
+        return image.devicePixelRatio() * QPaintDevice::devicePixelRatioFScale;
+
     default:
         qWarning("QRasterPlatformPixmap::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/opengl/qopenglpaintdevice.cpp b/src/gui/opengl/qopenglpaintdevice.cpp
index c0657feaa0..51086ffe65 100644
--- a/src/gui/opengl/qopenglpaintdevice.cpp
+++ b/src/gui/opengl/qopenglpaintdevice.cpp
@@ -271,6 +271,9 @@ int QOpenGLPaintDevice::metric(QPaintDevice::PaintDeviceMetric metric) const
         return qRound(d_ptr->dpmy * 0.0254);
     case PdmDevicePixelRatio:
         return d_ptr->devicePixelRatio;
+    case PdmDevicePixelRatioScaled:
+        return d_ptr->devicePixelRatio * QPaintDevice::devicePixelRatioFScale;
+
     default:
         qWarning("QOpenGLPaintDevice::metric() - metric %d not known", metric);
         return 0;
diff --git a/src/gui/painting/qpaintdevice.cpp b/src/gui/painting/qpaintdevice.cpp
index 36e0bbe223..4ee3d91ea3 100644
--- a/src/gui/painting/qpaintdevice.cpp
+++ b/src/gui/painting/qpaintdevice.cpp
@@ -41,6 +41,8 @@ QPaintDevice::QPaintDevice()
     painters = 0;
 }
 
+qreal QPaintDevice::devicePixelRatioFScale = 10000000.0;
+
 QPaintDevice::~QPaintDevice()
 {
     if (paintingActive())
@@ -79,7 +81,13 @@ Q_GUI_EXPORT int qt_paint_device_metric(const QPaintDevice *device, QPaintDevice
 
 int QPaintDevice::metric(PaintDeviceMetric m) const
 {
+    // Fallback: A subclass has not implemented PdmDevicePixelRatioScaled but might
+    // have implemented PdmDevicePixelRatio.
+    if (m == PdmDevicePixelRatioScaled)
+        return this->metric(PdmDevicePixelRatio) * devicePixelRatioFScale;
+
     qWarning("QPaintDevice::metrics: Device has no metric information");
+
     if (m == PdmDpiX) {
         return 72;
     } else if (m == PdmDpiY) {
@@ -95,4 +103,5 @@ int QPaintDevice::metric(PaintDeviceMetric m) const
     }
 }
 
+
 QT_END_NAMESPACE
diff --git a/src/gui/painting/qpaintdevice.h b/src/gui/painting/qpaintdevice.h
index 7c756c66de..819116c585 100644
--- a/src/gui/painting/qpaintdevice.h
+++ b/src/gui/painting/qpaintdevice.h
@@ -58,7 +58,8 @@ public:
         PdmDpiY,
         PdmPhysicalDpiX,
         PdmPhysicalDpiY,
-        PdmDevicePixelRatio
+        PdmDevicePixelRatio,
+        PdmDevicePixelRatioScaled
     };
 
     virtual ~QPaintDevice();
@@ -76,9 +77,13 @@ public:
     int physicalDpiX() const { return metric(PdmPhysicalDpiX); }
     int physicalDpiY() const { return metric(PdmPhysicalDpiY); }
     int devicePixelRatio() const { return metric(PdmDevicePixelRatio); }
+    qreal devicePixelRatioF()  const { return metric(PdmDevicePixelRatioScaled) / devicePixelRatioFScale; }
     int colorCount() const { return metric(PdmNumColors); }
     int depth() const { return metric(PdmDepth); }
 
+    // ### Classes that are not QPaintDevice subclasses are implementing metric()
+    // ### There needs to be some kind of (semi)-public API.
+    static qreal devicePixelRatioFScale;
 protected:
     QPaintDevice();
     virtual int metric(PaintDeviceMetric metric) const;
@@ -87,7 +92,6 @@ protected:
     virtual QPainter *sharedPainter() const;
 
     ushort        painters;                        // refcount
-
 private:
     Q_DISABLE_COPY(QPaintDevice)
 
diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 6f00abfc5f..69cbb42923 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -219,7 +219,7 @@ QTransform QPainterPrivate::viewTransform() const
     return QTransform();
 }
 
-int QPainterPrivate::effectiveDevicePixelRatio() const
+qreal QPainterPrivate::effectiveDevicePixelRatio() const
 {
     // Special cases for devices that does not support PdmDevicePixelRatio go here:
     if (device->devType() == QInternal::Printer)
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 7c32dc1694..fdad8e2460 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -241,7 +241,7 @@ public:
     }
 
     QTransform viewTransform() const;
-    int effectiveDevicePixelRatio() const;
+    qreal effectiveDevicePixelRatio() const;
     QTransform hidpiScaleTransform() const;
     static bool attachPainterPrivate(QPainter *q, QPaintDevice *pdev);
     void detachPainterPrivate(QPainter *q);
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index fc1280bfc4..38643c50da 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -4493,7 +4493,7 @@ QImage QGLWidget::grabFrameBuffer(bool withAlpha)
 {
     makeCurrent();
     QImage res;
-    qreal pixelRatio = devicePixelRatio();
+    qreal pixelRatio = devicePixelRatioF();
     int w = pixelRatio * width();
     int h = pixelRatio * height();
     if (format().rgba())
diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 8faa9f8681..8c60818819 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -671,7 +671,7 @@ void QOpenGLWidgetPrivate::recreateFbo()
     format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
     format.setSamples(samples);
 
-    const QSize deviceSize = q->size() * q->devicePixelRatio();
+    const QSize deviceSize = q->size() * q->devicePixelRatioF();
     fbo = new QOpenGLFramebufferObject(deviceSize, format);
     if (samples > 0)
         resolvedFbo = new QOpenGLFramebufferObject(deviceSize);
@@ -680,7 +680,7 @@ void QOpenGLWidgetPrivate::recreateFbo()
     context->functions()->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
 
     paintDevice->setSize(deviceSize);
-    paintDevice->setDevicePixelRatio(q->devicePixelRatio());
+    paintDevice->setDevicePixelRatio(q->devicePixelRatioF());
 
     emit q->resized();
 }
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index ad0142c5df..2d76cee008 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -12654,6 +12654,9 @@ int QWidget::metric(PaintDeviceMetric m) const
         return qRound(screen->physicalDotsPerInchY());
     } else if (m == PdmDevicePixelRatio) {
         return topLevelWindow ? topLevelWindow->devicePixelRatio() : qApp->devicePixelRatio();
+    } else if (m == PdmDevicePixelRatioScaled) {
+        return (topLevelWindow ? topLevelWindow->devicePixelRatio() : qApp->devicePixelRatio())
+            * QPaintDevice::devicePixelRatioFScale;
     } else {
         val = QPaintDevice::metric(m);// XXX
     }
diff --git a/src/widgets/styles/qmacstyle_mac.mm b/src/widgets/styles/qmacstyle_mac.mm
index 67970ba33d..95a41b4830 100644
--- a/src/widgets/styles/qmacstyle_mac.mm
+++ b/src/widgets/styles/qmacstyle_mac.mm
@@ -1989,7 +1989,7 @@ void QMacStylePrivate::drawColorlessButton(const HIRect &macRect, HIThemeButtonD
         }
     }
 
-    int devicePixelRatio = p->device()->devicePixelRatio();
+    int devicePixelRatio = p->device()->devicePixelRatioF();
     int width = devicePixelRatio * (int(macRect.size.width) + extraWidth);
     int height = devicePixelRatio * (int(macRect.size.height) + extraHeight);
 
@@ -7216,7 +7216,7 @@ CGContextRef qt_mac_cg_context(const QPaintDevice *pdev)
         }
 
         CGContextTranslateCTM(ret, 0, pm->height());
-        int devicePixelRatio = pdev->devicePixelRatio();
+        qreal devicePixelRatio = pdev->devicePixelRatioF();
         CGContextScaleCTM(ret, devicePixelRatio, devicePixelRatio);
         CGContextScaleCTM(ret, 1, -1);
         return ret;