smart way to identify plasma theme hasShadows

--many plasma themes disable their shadows with
settings their opacity to zero instead of removing
their shadow elements. In such case the new approach
sets the hasShadow flag to zero

app/plasma/extended/panelbackground.cpp

@@ -20,6 +20,9 @@
 
 #include "panelbackground.h"
 
+// local
+#include "theme.h"
+
 // Qt
 #include <QDebug>
 #include <QImage>
@@ -31,9 +34,10 @@
 namespace Latte {
 namespace PlasmaExtended {
 
-PanelBackground::PanelBackground(Plasma::Types::Location edge, QObject *parent)
+PanelBackground::PanelBackground(Plasma::Types::Location edge, Theme *parent)
     : QObject(parent),
-      m_location(edge)
+      m_location(edge),
+      m_parentTheme(parent)
 {
 }
 
@@ -143,35 +147,6 @@ void PanelBackground::updatePaddings(Plasma::Svg *svg)
     emit paddingsChanged();
 }
 
-bool PanelBackground::hasVisibleShadow(Plasma::Svg *svg) const
-{
-    if (!svg || !svg->hasElement("shadow-topleft")) {
-        return false;
-    }
-
-    QString cornerId = "shadow-topleft";
-    QImage corner = svg->image(svg->elementSize(cornerId), cornerId);
-
-    int fullTransparentPixels = 0;
-
-    for(int c=0; c<corner.width(); ++c) {
-        for(int r=0; r<corner.height(); ++r) {
-            QRgb *line = (QRgb *)corner.scanLine(r);
-            QRgb point = line[c];
-
-            if (qAlpha(point) == 0) {
-                fullTransparentPixels++;
-            }
-        }
-    }
-
-    int pixels = (corner.width() * corner.height());
-
-    qDebug() << "  PLASMA THEME TOPLEFT SHADOW :: pixels : " << pixels << "  transparent pixels" << fullTransparentPixels;
-
-    return (fullTransparentPixels != pixels );
-}
-
 void PanelBackground::updateRoundnessFromShadows(Plasma::Svg *svg)
 {
     if (!svg) {
@@ -353,7 +328,7 @@ void PanelBackground::updateRoundness(Plasma::Svg *svg)
         return;
     }
 
-    if (hasVisibleShadow(svg)) {
+    if (m_parentTheme->hasShadow()) {
         qDebug() << "PLASMA THEME, calculating roundness from shadows...";
         updateRoundnessFromShadows(svg);
     } else {

app/plasma/extended/panelbackground.h

@@ -28,6 +28,12 @@
 #include <Plasma>
 #include <Plasma/FrameSvg>
 
+namespace Latte {
+namespace PlasmaExtended {
+class Theme;
+}
+}
+
 namespace Latte {
 namespace PlasmaExtended {
 
@@ -44,7 +50,7 @@ class PanelBackground: public QObject
     Q_PROPERTY(float maxOpacity READ maxOpacity NOTIFY maxOpacityChanged)
 
 public:
-    PanelBackground(Plasma::Types::Location edge, QObject *parent);
+    PanelBackground(Plasma::Types::Location edge, Theme *parent);
     ~PanelBackground();
 
     int paddingTop() const;
@@ -65,8 +71,6 @@ signals:
     void maxOpacityChanged();
 
 private:
-    bool hasVisibleShadow(Plasma::Svg *svg) const;
-
     QString prefixed(const QString &id);
     QString element(Plasma::Svg *svg, const QString &id);
 
@@ -89,6 +93,7 @@ private:
 
     Plasma::Types::Location m_location{Plasma::Types::BottomEdge};
 
+    Theme *m_parentTheme{nullptr};
 };
 
 }

app/plasma/extended/theme.cpp

@@ -82,7 +82,6 @@ Theme::Theme(KSharedConfig::Ptr config, QObject *parent) :
     connect(this, &Theme::compositingChanged, this, &Theme::updateBackgrounds);
     connect(this, &Theme::outlineWidthChanged, this, &Theme::saveConfig);
 
-    connect(&m_theme, &Plasma::Theme::themeChanged, this, &Theme::hasShadowChanged);
     connect(&m_theme, &Plasma::Theme::themeChanged, this, &Theme::load);
     connect(&m_theme, &Plasma::Theme::themeChanged, this, &Theme::themeChanged);
 }
@@ -103,7 +102,7 @@ Theme::~Theme()
 
 bool Theme::hasShadow() const
 {
-    return PanelShadows::self()->hasShadows();
+    return m_hasShadow;
 }
 
 bool Theme::isLightTheme() const
@@ -310,12 +309,46 @@ void Theme::updateReversedSchemeValues()
 
 void Theme::updateBackgrounds()
 {
+    updateHasShadow();
+
     m_backgroundTopEdge->update();
     m_backgroundLeftEdge->update();
     m_backgroundBottomEdge->update();
     m_backgroundRightEdge->update();
 }
 
+void Theme::updateHasShadow()
+{
+    Plasma::Svg *svg = new Plasma::Svg(this);
+    svg->setImagePath(QStringLiteral("widgets/panel-background"));
+    svg->resize();
+
+    QString cornerId = "shadow-topleft";
+    QImage corner = svg->image(svg->elementSize(cornerId), cornerId);
+
+    int fullTransparentPixels = 0;
+
+    for(int c=0; c<corner.width(); ++c) {
+        for(int r=0; r<corner.height(); ++r) {
+            QRgb *line = (QRgb *)corner.scanLine(r);
+            QRgb point = line[c];
+
+            if (qAlpha(point) == 0) {
+                fullTransparentPixels++;
+            }
+        }
+    }
+
+    int pixels = (corner.width() * corner.height());
+
+    m_hasShadow = (fullTransparentPixels != pixels );
+    emit hasShadowChanged();
+
+    qDebug() << "  PLASMA THEME TOPLEFT SHADOW :: pixels : " << pixels << "  transparent pixels" << fullTransparentPixels << " | HAS SHADOWS :" << m_hasShadow;
+
+    svg->deleteLater();
+}
+
 void Theme::loadThemePaths()
 {
     m_themePath = Layouts::Importer::standardPath("plasma/desktoptheme/" + m_theme.themeName());

app/plasma/extended/theme.h

@@ -110,6 +110,7 @@ private:
     void updateBackgrounds();
 
     void setOriginalSchemeFile(const QString &file);
+    void updateHasShadow();
     void updateDefaultScheme();
     void updateDefaultSchemeValues();
     void updateReversedScheme();
@@ -118,6 +119,7 @@ private:
     void qmlRegisterTypes();
 
 private:
+    bool m_hasShadow{false};
     bool m_isLightTheme{false};
     bool m_compositing{true};
 

shell/package/contents/configuration/pages/AppearanceConfig.qml

@@ -1035,7 +1035,7 @@ PlasmaComponents.Page {
                         text: i18n("Shadows")
                         checked: plasmoid.configuration.panelShadows
                         checkable: true
-                        enabled: showBackground.checked && LatteCore.WindowSystem.compositingActive
+                        enabled: showBackground.checked && LatteCore.WindowSystem.compositingActive && themeExtended.hasShadow
                         tooltip: i18n("Background shows its shadows")
 
                         onClicked: {