Enable non-integer device pixel ratio

Work around QPaintDevice::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 QPaintDevice::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 QPaintDevice::devicePixelRatio()
to use QPainDevice::devicePixelRatioF().

Task-number: QTBUG-46615
Change-Id: I97ec4000fe379b7ff5e1624a871ae2512790aad9
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

5 files changed, 32 insertions, 25 deletions

diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 1ee28f2e9a..ea7a761bf1 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -695,7 +695,7 @@ 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);
@@ -704,7 +704,7 @@ 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();
 }
@@ -778,8 +778,8 @@ void QOpenGLWidgetPrivate::initialize()
     }
 
     paintDevice = new QOpenGLWidgetPaintDevice(q);
-    paintDevice->setSize(q->size() * q->devicePixelRatio());
-    paintDevice->setDevicePixelRatio(q->devicePixelRatio());
+    paintDevice->setSize(q->size() * q->devicePixelRatioF());
+    paintDevice->setDevicePixelRatio(q->devicePixelRatioF());
 
     context = ctx.take();
     initialized = true;
@@ -808,7 +808,7 @@ void QOpenGLWidgetPrivate::invokeUserPaint()
     QOpenGLFunctions *f = ctx->functions();
     QOpenGLContextPrivate::get(ctx)->defaultFboRedirect = fbo->handle();
 
-    f->glViewport(0, 0, q->width() * q->devicePixelRatio(), q->height() * q->devicePixelRatio());
+    f->glViewport(0, 0, q->width() * q->devicePixelRatioF(), q->height() * q->devicePixelRatioF());
     q->paintGL();
     flushPending = true;
 
@@ -859,8 +859,8 @@ QImage QOpenGLWidgetPrivate::grabFramebuffer()
     render();
     resolveSamples();
     q->makeCurrent();
-    QImage res = qt_gl_read_framebuffer(q->size() * q->devicePixelRatio(), false, false);
-    res.setDevicePixelRatio(q->devicePixelRatio());
+    QImage res = qt_gl_read_framebuffer(q->size() * q->devicePixelRatioF(), false, false);
+    res.setDevicePixelRatio(q->devicePixelRatioF());
 
     return res;
 }
@@ -879,7 +879,7 @@ void QOpenGLWidgetPrivate::resizeViewportFramebuffer()
     if (!initialized)
         return;
 
-    if (!fbo || q->size() * q->devicePixelRatio() != fbo->size())
+    if (!fbo || q->size() * q->devicePixelRatioF() != fbo->size())
         recreateFbo();
 }
 
@@ -1196,6 +1196,7 @@ int QOpenGLWidget::metric(QPaintDevice::PaintDeviceMetric metric) const
         return QWidget::metric(metric);
 
     QWidget *tlw = window();
+    QWindow *window = tlw ? tlw->windowHandle() : 0;
     QScreen *screen = tlw && tlw->windowHandle() ? tlw->windowHandle()->screen() : 0;
     if (!screen && QGuiApplication::primaryScreen())
         screen = QGuiApplication::primaryScreen();
@@ -1243,8 +1244,13 @@ int QOpenGLWidget::metric(QPaintDevice::PaintDeviceMetric metric) const
         else
             return qRound(dpmy * 0.0254);
     case PdmDevicePixelRatio:
-        if (screen)
-            return screen->devicePixelRatio();
+        if (window)
+            return int(window->devicePixelRatio());
+        else
+            return 1.0;
+    case PdmDevicePixelRatioScaled:
+        if (window)
+            return int(window->devicePixelRatio() * devicePixelRatioFScale());
         else
             return 1.0;
     default:
@@ -1304,7 +1310,7 @@ bool QOpenGLWidget::event(QEvent *e)
         }
         break;
     case QEvent::ScreenChangeInternal:
-        if (d->initialized && d->paintDevice->devicePixelRatio() != devicePixelRatio())
+        if (d->initialized && d->paintDevice->devicePixelRatioF() != devicePixelRatioF())
             d->recreateFbo();
         break;
     default:
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index c3fed921f9..06c42ff041 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -2035,7 +2035,7 @@ void QWidgetPrivate::setSystemClip(QPaintDevice *paintDevice, const QRegion &reg
 // Transform the system clip region from device-independent pixels to device pixels
     QPaintEngine *paintEngine = paintDevice->paintEngine();
     QTransform scaleTransform;
-    const qreal devicePixelRatio = paintDevice->devicePixelRatio();
+    const qreal devicePixelRatio = paintDevice->devicePixelRatioF();
     scaleTransform.scale(devicePixelRatio, devicePixelRatio);
     paintEngine->d_func()->systemClip = scaleTransform.map(region);
 }
@@ -5361,7 +5361,7 @@ void QWidgetPrivate::render_helper(QPainter *painter, const QPoint &targetOffset
         if (size.isNull())
             return;
 
-        const qreal pixmapDevicePixelRatio = qreal(painter->device()->devicePixelRatio());
+        const qreal pixmapDevicePixelRatio = painter->device()->devicePixelRatioF();
         QPixmap pixmap(size * pixmapDevicePixelRatio);
         pixmap.setDevicePixelRatio(pixmapDevicePixelRatio);
 
@@ -11833,13 +11833,11 @@ void QWidgetPrivate::updateFrameStrut()
     Q_Q(QWidget);
     if (q->data->fstrut_dirty) {
         if (QTLWExtra *te = maybeTopData()) {
-            if (te->window) {
-                if (const QPlatformWindow *pw = te->window->handle()) {
-                    const QMargins margins = pw->frameMargins();
-                    if (!margins.isNull()) {
-                        te->frameStrut.setCoords(margins.left(), margins.top(), margins.right(), margins.bottom());
-                        q->data->fstrut_dirty = false;
-                    }
+            if (te->window && te->window->handle()) {
+                const QMargins margins = te->window->frameMargins();
+                if (!margins.isNull()) {
+                    te->frameStrut.setCoords(margins.left(), margins.top(), margins.right(), margins.bottom());
+                    q->data->fstrut_dirty = false;
                 }
             }
         }
@@ -12658,6 +12656,9 @@ 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 (QPaintDevice::devicePixelRatioFScale() *
+                (topLevelWindow ? topLevelWindow->devicePixelRatio() : qApp->devicePixelRatio()));
     } else {
         val = QPaintDevice::metric(m);// XXX
     }
@@ -12873,7 +12874,7 @@ QDebug operator<<(QDebug debug, const QWidget *widget)
                                        frameGeometry.bottom() - geometry.bottom());
                 debug << ", margins=" << margins;
             }
-            debug << ", devicePixelRatio=" << widget->devicePixelRatio();
+            debug << ", devicePixelRatio=" << widget->devicePixelRatioF();
             if (const WId wid = widget->internalWinId())
                 debug << ", winId=0x" << hex << wid << dec;
         }
diff --git a/src/widgets/styles/qmacstyle_mac.mm b/src/widgets/styles/qmacstyle_mac.mm
index f4686f2810..aa1a783577 100644
--- a/src/widgets/styles/qmacstyle_mac.mm
+++ b/src/widgets/styles/qmacstyle_mac.mm
@@ -1972,7 +1972,7 @@ 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);
 
@@ -7199,7 +7199,7 @@ 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;
diff --git a/src/widgets/styles/qwindowsstyle_p_p.h b/src/widgets/styles/qwindowsstyle_p_p.h
index 3d1206b369..c8778cc914 100644
--- a/src/widgets/styles/qwindowsstyle_p_p.h
+++ b/src/widgets/styles/qwindowsstyle_p_p.h
@@ -65,7 +65,7 @@ public:
     static int pixelMetricFromSystemDp(QStyle::PixelMetric pm, const QStyleOption *option = 0, const QWidget *widget = 0);
     static int fixedPixelMetric(QStyle::PixelMetric pm);
     static int devicePixelRatio(const QWidget *widget = 0)
-        { return widget ? widget->devicePixelRatio() : QWindowsStylePrivate::appDevicePixelRatio(); }
+        { return widget ? int(widget->devicePixelRatioF()) : QWindowsStylePrivate::appDevicePixelRatio(); }
 
     bool hasSeenAlt(const QWidget *widget) const;
     bool altDown() const { return alt_down; }
diff --git a/src/widgets/widgets/qlabel.cpp b/src/widgets/widgets/qlabel.cpp
index e58a3e8211..55e277026c 100644
--- a/src/widgets/widgets/qlabel.cpp
+++ b/src/widgets/widgets/qlabel.cpp
@@ -1096,7 +1096,7 @@ void QLabel::paintEvent(QPaintEvent *)
                     d->cachedimage = new QImage(d->pixmap->toImage());
                 delete d->scaledpixmap;
                 QImage scaledImage =
-                    d->cachedimage->scaled(cr.size() * devicePixelRatio(),
+                    d->cachedimage->scaled(cr.size() * devicePixelRatioF(),
                                            Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
                 d->scaledpixmap = new QPixmap(QPixmap::fromImage(scaledImage));
             }