Qt Designer: Adapt the new form dialog to High DPI.

Propagate the device pixel ratio obtained from QWidget::grab()
and determine the size depending on screen size so that it is reasonable
with or without High DPI scaling.

Task-number: QTBUG-53713
Change-Id: I2a0dd1df91fccd455707ab23205e2e5ad592d570
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

1 files changed, 24 insertions, 17 deletions

diff --git a/src/designer/src/lib/shared/newformwidget.cpp b/src/designer/src/lib/shared/newformwidget.cpp
index b2b0640a2..d7ae18a87 100644
--- a/src/designer/src/lib/shared/newformwidget.cpp
+++ b/src/designer/src/lib/shared/newformwidget.cpp
@@ -53,6 +53,8 @@
 #include <QtCore/QDir>
 #include <QtCore/QTextStream>
 
+#include <QtWidgets/QApplication>
+#include <QtWidgets/QDesktopWidget>
 #include <QtWidgets/QHeaderView>
 #include <QtWidgets/QTreeWidgetItem>
 #include <QtGui/QPainter>
@@ -320,18 +322,23 @@ QImage NewFormWidget::grabForm(QDesignerFormEditorInterface *core,
 
 QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &workingDir) const
 {
-    const int margin = 7;
-    const int shadow = 7;
-    const int previewSize = 256;
+    const QSizeF screenSize(QApplication::desktop()->screenGeometry(this).size());
+    const int previewSize = qRound(screenSize.width() / 7.5); // 256 on 1920px screens.
+    const int margin = previewSize / 32 - 1; // 7 on 1920px screens.
+    const int shadow = margin;
 
     const QImage wimage = grabForm(m_core, file, workingDir,  currentDeviceProfile());
     if (wimage.isNull())
         return QPixmap();
-    const QImage image =  wimage.scaled(previewSize - margin * 2, previewSize - margin * 2,
-                                        Qt::KeepAspectRatio,
-                                        Qt::SmoothTransformation);
-
-    QImage dest(previewSize, previewSize, QImage::Format_ARGB32_Premultiplied);
+    const qreal devicePixelRatio = wimage.devicePixelRatioF();
+    const QSize imageSize(previewSize - margin * 2, previewSize - margin * 2);
+    QImage image = wimage.scaled((QSizeF(imageSize) * devicePixelRatio).toSize(),
+                                 Qt::KeepAspectRatio, Qt::SmoothTransformation);
+    image.setDevicePixelRatio(devicePixelRatio);
+
+    QImage dest((QSizeF(previewSize, previewSize) * devicePixelRatio).toSize(),
+                QImage::Format_ARGB32_Premultiplied);
+    dest.setDevicePixelRatio(devicePixelRatio);
     dest.fill(0);
 
     QPainter p(&dest);
@@ -339,14 +346,14 @@ QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &working
 
     p.setPen(QPen(palette().brush(QPalette::WindowText), 0));
 
-    p.drawRect(margin-1, margin-1, image.width() + 1, image.height() + 1);
+    p.drawRect(QRectF(margin - 1, margin - 1, imageSize.width() + 1.5, imageSize.height() + 1.5));
 
     const QColor dark(Qt::darkGray);
     const QColor light(Qt::transparent);
 
     // right shadow
     {
-        const QRect rect(margin + image.width() + 1, margin + shadow, shadow, image.height() - shadow + 1);
+        const QRect rect(margin + imageSize.width() + 1, margin + shadow, shadow, imageSize.height() - shadow + 1);
         QLinearGradient lg(rect.topLeft(), rect.topRight());
         lg.setColorAt(0, dark);
         lg.setColorAt(1, light);
@@ -355,7 +362,7 @@ QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &working
 
     // bottom shadow
     {
-        const QRect rect(margin + shadow, margin + image.height() + 1, image.width() - shadow + 1, shadow);
+        const QRect rect(margin + shadow, margin + imageSize.height() + 1, imageSize.width() - shadow + 1, shadow);
         QLinearGradient lg(rect.topLeft(), rect.bottomLeft());
         lg.setColorAt(0, dark);
         lg.setColorAt(1, light);
@@ -364,8 +371,8 @@ QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &working
 
     // bottom/right corner shadow
     {
-        const QRect rect(margin + image.width() + 1, margin + image.height() + 1, shadow, shadow);
-        QRadialGradient g(rect.topLeft(), shadow);
+        const QRect rect(margin + imageSize.width() + 1, margin + imageSize.height() + 1, shadow, shadow);
+        QRadialGradient g(rect.topLeft(), shadow - 1);
         g.setColorAt(0, dark);
         g.setColorAt(1, light);
         p.fillRect(rect, g);
@@ -373,8 +380,8 @@ QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &working
 
     // top/right corner
     {
-        const QRect rect(margin + image.width() + 1, margin, shadow, shadow);
-        QRadialGradient g(rect.bottomLeft(), shadow);
+        const QRect rect(margin + imageSize.width() + 1, margin, shadow, shadow);
+        QRadialGradient g(rect.bottomLeft(), shadow - 1);
         g.setColorAt(0, dark);
         g.setColorAt(1, light);
         p.fillRect(rect, g);
@@ -382,8 +389,8 @@ QPixmap NewFormWidget::formPreviewPixmap(QIODevice &file, const QString &working
 
     // bottom/left corner
     {
-        const QRect rect(margin, margin + image.height() + 1, shadow, shadow);
-        QRadialGradient g(rect.topRight(), shadow);
+        const QRect rect(margin, margin + imageSize.height() + 1, shadow, shadow);
+        QRadialGradient g(rect.topRight(), shadow - 1);
         g.setColorAt(0, dark);
         g.setColorAt(1, light);
         p.fillRect(rect, g);