Force basic render loop and add some debug logs.

app/main.cpp

@@ -8,6 +8,7 @@
 #include <QIcon>
 #include <QQuickStyle>
 #include <QtQml/qqml.h>
+#include <QQuickWindow>
 
 #include <kdsingleapplication.h>
 
@@ -44,9 +45,10 @@ int main(int argc, char *argv[])
     QLoggingCategory::setFilterRules("qt.qml.connections.warning=false");
     QGuiApplication::setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy::Round);
 
-// #if defined (Q_OS_LINUX)
-//     setenv("QSG_RENDER_LOOP", "threaded", 0);
-// #endif
+// Set render loop to basic for debug/test builds.
+#if defined (Q_OS_LINUX)
+    setenv("QSG_RENDER_LOOP", "basic", 0);
+#endif
 
 #if defined(Q_OS_MAC)
     // This allows UTF-8 characters usage in OSX.
@@ -88,6 +90,12 @@ int main(int argc, char *argv[])
     app.setOrganizationDomain(QStringLiteral("cool-retro-term"));
     app.setApplicationVersion(appVersion);
 
+    qInfo() << "cool-retro-term version" << appVersion;
+    qInfo() << "Qt version" << QT_VERSION_STR;
+    qInfo() << "Platform" << QGuiApplication::platformName();
+    qInfo() << "QSG_RENDER_LOOP" << qgetenv("QSG_RENDER_LOOP");
+    qInfo() << "QQuickWindow graphicsApi" << QQuickWindow::graphicsApi();
+
     KDSingleApplication singleApp(QStringLiteral("cool-retro-term"));
 
     if (!singleApp.isPrimaryInstance()) {

app/qml/ApplicationSettings.qml

@@ -38,6 +38,7 @@ QtObject {
     readonly property real maxBurnInFadeTime: 1.6
 
     property bool isMacOS: Qt.platform.os === "osx"
+    property bool isLinux: Qt.platform.os === "linux"
 
     // GENERAL SETTINGS ///////////////////////////////////////////////////////
     property bool showMenubar: false
@@ -52,6 +53,7 @@ QtObject {
     property real burnInQuality: 0.5
 
     property bool blinkingCursor: false
+    property bool preferAcceleratedFontRendering: false
 
 
     // PROFILE SETTINGS ///////////////////////////////////////////////////////
@@ -167,7 +169,8 @@ QtObject {
             "bloomQuality": bloomQuality,
             "burnInQuality": burnInQuality,
             "useCustomCommand": useCustomCommand,
-            "customCommand": customCommand
+            "customCommand": customCommand,
+            "preferAcceleratedFontRendering": preferAcceleratedFontRendering
         }
         return stringify(settings)
     }
@@ -260,6 +263,8 @@ QtObject {
                 !== undefined ? settings.useCustomCommand : useCustomCommand
         customCommand = settings.customCommand
                 !== undefined ? settings.customCommand : customCommand
+        preferAcceleratedFontRendering = settings.preferAcceleratedFontRendering
+                !== undefined ? settings.preferAcceleratedFontRendering : preferAcceleratedFontRendering
     }
 
     function loadProfileString(profileString) {

app/qml/PreprocessedTerminal.qml

@@ -93,16 +93,16 @@ Item{
 
         property int textureResolutionScale: appSettings.lowResolutionFont ? Screen.devicePixelRatio : 1
         property int margin: appSettings.margin / screenScaling
-        property int totalWidth: Math.floor(parent.width / (screenScaling * fontWidth))
-        property int totalHeight: Math.floor(parent.height / screenScaling)
+        property int totalWidth: Math.max(1, Math.floor(parent.width / (screenScaling * fontWidth)))
+        property int totalHeight: Math.max(1, Math.floor(parent.height / screenScaling))
 
-        property int rawWidth: totalWidth - 2 * margin
-        property int rawHeight: totalHeight - 2 * margin
+        property int rawWidth: Math.max(1, totalWidth - 2 * margin)
+        property int rawHeight: Math.max(1, totalHeight - 2 * margin)
 
         textureSize: Qt.size(width / textureResolutionScale, height / textureResolutionScale)
 
-        width: ensureMultiple(rawWidth, Screen.devicePixelRatio)
-        height: ensureMultiple(rawHeight, Screen.devicePixelRatio)
+        width: Math.max(1, ensureMultiple(rawWidth, Screen.devicePixelRatio))
+        height: Math.max(1, ensureMultiple(rawHeight, Screen.devicePixelRatio))
 
         /** Ensure size is a multiple of factor. This is needed for pixel perfect scaling on highdpi screens. */
         function ensureMultiple(size, factor) {
@@ -111,6 +111,7 @@ Item{
 
         fullCursorHeight: true
         blinkingCursor: appSettings.blinkingCursor
+        useFBORendering: appSettings.preferAcceleratedFontRendering
 
         colorScheme: "cool-retro-term"
 
@@ -266,8 +267,11 @@ Item{
         hideSource: true
         wrapMode: ShaderEffectSource.Repeat
         visible: false
-        textureSize: Qt.size(kterminal.totalWidth * scaleTexture, kterminal.totalHeight * scaleTexture)
-        sourceRect: Qt.rect(-kterminal.margin, -kterminal.margin, kterminal.totalWidth, kterminal.totalHeight)
+        textureSize: Qt.size(Math.max(1, kterminal.totalWidth * scaleTexture),
+                             Math.max(1, kterminal.totalHeight * scaleTexture))
+        sourceRect: Qt.rect(-kterminal.margin, -kterminal.margin,
+                            Math.max(1, kterminal.totalWidth),
+                            Math.max(1, kterminal.totalHeight))
     }
 
     Item {

app/qml/SettingsAdvancedTab.qml

@@ -146,6 +146,14 @@ ColumnLayout {
             SizedLabel {
                 text: Math.round(burnInSlider.value * 100) + "%"
             }
+
+            CheckBox {
+                Layout.columnSpan: 4
+                text: qsTr("Prefer accelerated font rendering")
+                visible: appSettings.isLinux
+                checked: appSettings.preferAcceleratedFontRendering
+                onCheckedChanged: appSettings.preferAcceleratedFontRendering = checked
+            }
         }
     }
 }