Fix text scaling with non-integer scale factors when PLASMA_USE_QT_SCALING=1 is set

Summary:
When `PLASMA_USE_QT_SCALING=1` is set, Plasma uses native Qt scaling. This works fine for integer scale factors, and fixes a lot of bugs (see [[https://bugs.kde.org/show_bug.cgi?id=356446|Bug 356446]]) but it introduces a new one: with non-integer scale factors, text becomes blurry and pixellated because of a bug in `Text.NativeRendering`: https://bugreports.qt.io/browse/QTBUG-67007

QQC2-desktop-style forces the use of `Text.QtRendering` rendering for non-integer scale factors, successfully working around the problem. But PlasmaComponents QML objects don't implement the same workaround, so we see the issue in Plasma. This patch fixes that, and gets us one step closer to being able to use Qt scaling in Plasmashell.

There is no effect when `PLASMA_USE_QT_SCALING=1` is not being used.

FIXED-IN 5.13
BUG: 391691
BUG: 384031
CCBUG: 386216
CCBUG: 391695
CCBUG: 391694
CCBUG: 385547
CCBUG: 391692
CCBUG: 356446

Test Plan:
Before: `PLASMA_USE_QT_SCALING=1` set, 1.2 scale factor: Plasma text looks awful:
{F5749797}

After: `PLASMA_USE_QT_SCALING=1` set, 1.2 scale factor: Plasma text looks amazing!
{F5749798}

Note that we still get sub-pixel anti-aliasing and good kerning. There appear to be no layout regressions.

Without both `PLASMA_USE_QT_SCALING=1` and a non-integer scale factor set, there is no visual change compared to the status quo.

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: mart, broulik, #frameworks

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D11244

examples/applets/testtheme/contents/ui/FontGizmo.qml

@@ -17,7 +17,7 @@
  */
 
 import QtQuick 2.1
-
+import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
 
@@ -28,7 +28,9 @@ import org.kde.plasma.core 2.0 as PlasmaCore
 
 Text {
 
-    renderType: QtQuickControlsPrivate.Settings.isMobile ? Text.QtRendering : Text.NativeRendering
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: QtQuickControlsPrivate.Settings.isMobile || Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
     font.pointSize: 22
 
     //font.family: theme.defaultFont.family

src/declarativeimports/plasmacomponents/qml/Label.qml

@@ -18,6 +18,7 @@
 */
 
 import QtQuick 2.1
+import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -41,7 +42,10 @@ Text {
     verticalAlignment: lineCount > 1 ? Text.AlignTop : Text.AlignVCenter
 
     activeFocusOnTab: false
-    renderType: QtQuickControlsPrivate.Settings.isMobile ? Text.QtRendering : Text.NativeRendering
+
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: QtQuickControlsPrivate.Settings.isMobile || Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
 
     font.capitalization: theme.defaultFont.capitalization
     font.family: theme.defaultFont.family

src/declarativeimports/plasmacomponents/qml/private/DualStateButton.qml

@@ -18,6 +18,7 @@
 */
 
 import QtQuick 2.1
+import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -95,7 +96,10 @@ Item {
         id: label
 
         text: dualButton.text
-        renderType: QtQuickControlsPrivate.Settings.isMobile ? Text.QtRendering : Text.NativeRendering
+
+        // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+        // https://bugreports.qt.io/browse/QTBUG-67007
+        renderType: QtQuickControlsPrivate.Settings.isMobile || Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
         anchors {
             top: parent.top
             bottom: parent.bottom

src/declarativeimports/plasmacomponents3/ComboBox.qml

@@ -39,6 +39,10 @@ T.ComboBox {
     rightPadding: surfaceNormal.margins.right
     bottomPadding: surfaceNormal.margins.bottom
 
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
+
     delegate: ItemDelegate {
         width: control.popup.width
         text: control.textRole ? (Array.isArray(control.model) ? modelData[control.textRole] : model[control.textRole]) : modelData

src/declarativeimports/plasmacomponents3/Label.qml

@@ -18,6 +18,7 @@
  */
 
 import QtQuick 2.1
+import QtQuick.Window 2.2
 import QtQuick.Templates @QQC2_VERSION@ as T
 import org.kde.plasma.core 2.0 as PlasmaCore
 
@@ -27,7 +28,10 @@ T.Label {
     verticalAlignment: lineCount > 1 ? Text.AlignTop : Text.AlignVCenter
 
     activeFocusOnTab: false
-    renderType: Text.NativeRendering
+
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
 
     //font data is the system one by default
     //TODO: from theme singleton?

src/declarativeimports/plasmacomponents3/TextArea.qml

@@ -18,6 +18,7 @@
  */
 
 import QtQuick 2.6
+import QtQuick.Window 2.2
 import QtQuick.Controls @QQC2_VERSION@
 import QtQuick.Templates @QQC2_VERSION@ as T
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -41,7 +42,10 @@ T.TextArea {
     opacity: control.enabled ? 1 : 0.6
     wrapMode: Text.WordWrap
     verticalAlignment: TextEdit.AlignTop
-    renderType: Text.NativeRendering
+
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
     
     Label {
         id: placeholder

src/declarativeimports/plasmacomponents3/TextField.qml

@@ -18,6 +18,7 @@
  */
 
 import QtQuick 2.6
+import QtQuick.Window 2.2
 import QtQuick.Controls @QQC2_VERSION@
 import QtQuick.Templates @QQC2_VERSION@ as T
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -39,7 +40,10 @@ T.TextField {
     selectedTextColor: theme.highlightedTextColor
     verticalAlignment: TextInput.AlignVCenter
     opacity: control.enabled ? 1 : 0.6
-    renderType: Text.NativeRendering
+
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
 
     Label {
         id: placeholder

src/declarativeimports/plasmastyle/ComboBoxStyle.qml

@@ -18,6 +18,7 @@
 */
 
 import QtQuick 2.0
+import QtQuick.Window 2.2
 import QtQuick.Controls.Styles 1.1 as QtQuickControlStyle
 
 import org.kde.plasma.core 2.0 as PlasmaCore
@@ -28,6 +29,10 @@ import "private" as Private
 QtQuickControlStyle.ComboBoxStyle {
     drowDownButtonWidth: units.iconSizes.small
 
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
+
     label: PlasmaComponents.Label {
         text: control.currentText
         elide: Text.ElideRight

src/declarativeimports/plasmastyle/SpinBoxStyle.qml

@@ -19,6 +19,7 @@
  */
 
 import QtQuick 2.0
+import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Styles 1.1 as QtQuickControlStyle
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
@@ -40,7 +41,9 @@ QtQuickControlStyle.SpinBoxStyle {
     selectedTextColor: theme.viewBackgroundColor
 
 
-    renderType: QtQuickControlsPrivate.Settings.isMobile ? Text.QtRendering : Text.NativeRendering
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: QtQuickControlsPrivate.Settings.isMobile || Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
 
     PlasmaCore.Svg {
         id: arrowSvg

src/declarativeimports/plasmastyle/TextAreaStyle.qml

@@ -19,6 +19,7 @@
 
 
 import QtQuick 2.1
+import QtQuick.Window 2.2
 import QtQuick.Controls.Styles 1.1 as QtQuickControlStyle
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
 import QtQuick.Controls 1.1
@@ -41,7 +42,9 @@ QtQuickControlStyle.TextAreaStyle {
     selectionColor: control.backgroundVisible ? theme.viewFocusColor : PlasmaCore.ColorScope.highlightColor
     selectedTextColor: control.backgroundVisible ? theme.viewHighlightedTextColor : PlasmaCore.ColorScope.highlightedTextColor
 
-    renderType: QtQuickControlsPrivate.Settings.isMobile ? Text.QtRendering : Text.NativeRendering
+    // Work around Qt bug where NativeRendering breaks for non-integer scale factors
+    // https://bugreports.qt.io/browse/QTBUG-67007
+    renderType: QtQuickControlsPrivate.Settings.isMobile || Screen.devicePixelRatio % 1 !== 0 ? Text.QtRendering : Text.NativeRendering
 
     frame: PlasmaCore.FrameSvgItem {
         id: base

src/declarativeimports/plasmastyle/TextFieldStyle.qml

@@ -18,6 +18,7 @@
 */
 
 import QtQuick 2.0
+import QtQuick.Window 2.2
 import QtQuick.Controls 1.0
 import QtQuick.Controls.Styles 1.1 as QtQuickControlStyle
 import QtQuick.Controls.Private 1.0 as QtQuickControlsPrivate
@@ -40,8 +41,10 @@ QtQuickControlStyle.TextFieldStyle {
      * more blurred with different rendring types.
      * Using Qt rendering, the dots will look more aligned and equally spaced.
      * Also if we are on mobile, make sure we use QtRendering
+     * Finally, use QtRendering if we're using a non-integer scale factor to work around
+     * https://bugreports.qt.io/browse/QTBUG-67007
      */
-    renderType: !QtQuickControlsPrivate.Settings.isMobile && control.echoMode == TextInput.Normal ? Text.NativeRendering : Text.QtRendering
+    renderType: !QtQuickControlsPrivate.Settings.isMobile && control.echoMode == TextInput.Normal && Screen.devicePixelRatio % 1 == 0 ? Text.NativeRendering : Text.QtRendering
 
     background: Item {
         //QQC button heights are max(backgroundHeight, label + margins).