[Feature] Multi layer onion skinning

app/src/onionskinwidget.cpp

@@ -95,6 +95,7 @@ void OnionSkinWidget::makeConnections()
 
     connect(ui->onionSkinMode, &QCheckBox::stateChanged, this, &OnionSkinWidget::onionSkinModeChange);
     connect(ui->onionWhilePlayback, &QCheckBox::stateChanged, this, &OnionSkinWidget::playbackStateChanged);
+    connect(ui->onionSkinMultiLayer, &QCheckBox::stateChanged, this, &OnionSkinWidget::onionSkinMultipleLayersEnabled);
 
     PreferenceManager* prefs = editor()->preference();
     connect(prefs, &PreferenceManager::optionChanged, this, &OnionSkinWidget::updateUI);
@@ -123,8 +124,10 @@ void OnionSkinWidget::updateUI()
     ui->onionSkinMode->setChecked(prefs->getString(SETTING::ONION_TYPE) == "absolute");
 
     QSignalBlocker b6(ui->onionWhilePlayback);
-    ui->onionWhilePlayback->setChecked(prefs->getInt(SETTING::ONION_WHILE_PLAYBACK));
+    ui->onionWhilePlayback->setChecked(prefs->isOn(SETTING::ONION_WHILE_PLAYBACK));
 
+    QSignalBlocker b7(ui->onionSkinMultiLayer);
+    ui->onionSkinMultiLayer->setChecked(prefs->isOn(SETTING::ONION_MUTLIPLE_LAYERS));
 }
 
 void OnionSkinWidget::prevFramesGroupClicked(bool isOn)
@@ -193,3 +196,9 @@ void OnionSkinWidget::playbackStateChanged(int value)
     PreferenceManager* prefs = editor()->preference();
     prefs->set(SETTING::ONION_WHILE_PLAYBACK, value);
 }
+
+void OnionSkinWidget::onionSkinMultipleLayersEnabled(bool value)
+{
+    PreferenceManager* prefs = editor()->preference();
+    prefs->set(SETTING::ONION_MUTLIPLE_LAYERS, value);
+}

app/src/onionskinwidget.h

@@ -50,6 +50,7 @@ private slots:
     void onionPrevFramesNumChange(int);
     void onionNextFramesNumChange(int);
     void onionSkinModeChange(int);
+    void onionSkinMultipleLayersEnabled(bool value);
 
 private:
     void makeConnections();

app/ui/onionskin.ui

@@ -444,6 +444,20 @@
           <property name="topMargin">
            <number>0</number>
           </property>
+          <item>
+           <widget class="QCheckBox" name="onionSkinMultiLayer">
+            <property name="text">
+             <string>Show On All Layers</string>
+            </property>
+           </widget>
+          </item>
+          <item>
+           <widget class="Line" name="line">
+            <property name="orientation">
+             <enum>Qt::Horizontal</enum>
+            </property>
+           </widget>
+          </item>
           <item>
            <widget class="QCheckBox" name="onionSkinMode">
             <property name="text">

core_lib/src/canvaspainter.cpp

@@ -200,10 +200,8 @@ void CanvasPainter::paint(const QRect& blitRect)
     mPostLayersPixmapCacheValid = true;
 }
 
-void CanvasPainter::paintOnionSkin(QPainter& painter, const QRect& blitRect)
+void CanvasPainter::paintOnionSkinOnLayer(QPainter& painter, const QRect& blitRect, Layer* layer)
 {
-    Layer* layer = mObject->getLayer(mCurrentLayerIndex);
-
     mOnionSkinSubPainter.paint(painter, layer, mOnionSkinPainterOptions, mFrameNumber, [&] (OnionSkinPaintState state, int onionFrameNumber) {
         if (state == OnionSkinPaintState::PREV) {
             switch (layer->type())
@@ -224,6 +222,21 @@ void CanvasPainter::paintOnionSkin(QPainter& painter, const QRect& blitRect)
     });
 }
 
+void CanvasPainter::paintOnionSkin(QPainter& painter, const QRect& blitRect)
+{
+    if (!mOptions.bOnionSkinMultiLayer || mOptions.eLayerVisibility == LayerVisibility::CURRENTONLY) {
+        Layer* layer = mObject->getLayer(mCurrentLayerIndex);
+        paintOnionSkinOnLayer(painter, blitRect, layer);
+    } else {
+        for (int i = 0; i < mObject->getLayerCount(); i++) {
+            Layer* layer = mObject->getLayer(i);
+            if (layer == nullptr) { continue; }
+
+            paintOnionSkinOnLayer(painter, blitRect, layer);
+        }
+    }
+}
+
 void CanvasPainter::paintBitmapOnionSkinFrame(QPainter& painter, const QRect& blitRect, Layer* layer, int nFrame, bool colorize)
 {
     LayerBitmap* bitmapLayer = static_cast<LayerBitmap*>(layer);

core_lib/src/canvaspainter.h

@@ -44,6 +44,7 @@ struct CanvasPainterOptions
 
     LayerVisibility eLayerVisibility = LayerVisibility::RELATED;
     float fLayerVisibilityThreshold = 0.f;
+    bool bOnionSkinMultiLayer = false;
     float scaling = 1.0f;
     QPainter::CompositionMode cmBufferBlendMode = QPainter::CompositionMode_SourceOver;
     OnionSkinPainterOptions mOnionSkinOptions;
@@ -80,6 +81,7 @@ class CanvasPainter
      */
     void initializePainter(QPainter& painter, QPaintDevice& device, const QRect& blitRect);
 
+    void paintOnionSkinOnLayer(QPainter& painter, const QRect& blitRect, Layer* layer);
     void paintOnionSkin(QPainter& painter, const QRect& blitRect);
 
     void renderPostLayers(QPainter& painter, const QRect& blitRect);

core_lib/src/interface/scribblearea.cpp

@@ -87,8 +87,6 @@ bool ScribbleArea::init()
 
     mMakeInvisible = false;
 
-    mMultiLayerOnionSkin = mPrefs->isOn(SETTING::MULTILAYER_ONION);
-
     mLayerVisibility = static_cast<LayerVisibility>(mPrefs->getInt(SETTING::LAYER_VISIBILITY));
 
     mDeltaFactor = mEditor->preference()->isOn(SETTING::INVERT_SCROLL_ZOOM_DIRECTION) ? -1 : 1;
@@ -148,8 +146,7 @@ void ScribbleArea::settingUpdated(SETTING setting)
     case SETTING::ONION_WHILE_PLAYBACK:
         invalidateAllCache();
         break;
-    case SETTING::MULTILAYER_ONION:
-        mMultiLayerOnionSkin = mPrefs->isOn(SETTING::MULTILAYER_ONION);
+    case SETTING::ONION_MUTLIPLE_LAYERS:
         invalidateAllCache();
         break;
     case SETTING::LAYER_VISIBILITY_THRESHOLD:
@@ -1103,6 +1100,7 @@ void ScribbleArea::prepCanvas(int frame)
     Object* object = mEditor->object();
 
     CanvasPainterOptions o;
+    o.bOnionSkinMultiLayer = mPrefs->isOn(SETTING::ONION_MUTLIPLE_LAYERS);
     o.bAntiAlias = mPrefs->isOn(SETTING::ANTIALIAS);
     o.bThinLines = mPrefs->isOn(SETTING::INVISIBLE_LINES);
     o.bOutlines = mPrefs->isOn(SETTING::OUTLINES);

core_lib/src/interface/scribblearea.h

@@ -218,7 +218,6 @@ public slots:
     LayerVisibility mLayerVisibility = LayerVisibility::ALL;
     bool mMakeInvisible = false;
     qreal mCurveSmoothingLevel = 0.0;
-    bool mMultiLayerOnionSkin = false; // Future use. If required, just add a checkbox to update it.
     int mDeltaFactor = 1;
 
     /* Under certain circumstances a mouse press event will fire after a tablet release event.

core_lib/src/managers/preferencemanager.cpp

@@ -119,7 +119,7 @@ void PreferenceManager::loadPrefs()
     // Onion Skin
     set(SETTING::PREV_ONION,               settings.value(SETTING_PREV_ONION,             false).toBool());
     set(SETTING::NEXT_ONION,               settings.value(SETTING_NEXT_ONION,             false).toBool());
-    set(SETTING::MULTILAYER_ONION,         settings.value(SETTING_MULTILAYER_ONION,       false).toBool());
+    set(SETTING::ONION_MUTLIPLE_LAYERS,    settings.value(SETTING_MULTILAYER_ONION,       false).toBool());
     set(SETTING::ONION_BLUE,               settings.value(SETTING_ONION_BLUE,             false).toBool());
     set(SETTING::ONION_RED,                settings.value(SETTING_ONION_RED,              false).toBool());
 
@@ -403,7 +403,7 @@ void PreferenceManager::set(SETTING option, bool value)
     case SETTING::NEXT_ONION:
         settings.setValue(SETTING_NEXT_ONION, value);
         break;
-    case SETTING::MULTILAYER_ONION:
+    case SETTING::ONION_MUTLIPLE_LAYERS:
         settings.setValue(SETTING_MULTILAYER_ONION, value);
         break;
     case SETTING::INVISIBLE_LINES:

core_lib/src/util/preferencesdef.h

@@ -51,6 +51,7 @@ enum class SETTING
     ONION_PREV_FRAMES_NUM,
     ONION_NEXT_FRAMES_NUM,
     ONION_WHILE_PLAYBACK,
+    ONION_MUTLIPLE_LAYERS,
     ONION_TYPE,
     FLIP_ROLL_MSEC,
     FLIP_ROLL_DRAWINGS,
@@ -78,7 +79,6 @@ enum class SETTING
     QUICK_SIZING,
     INVERT_DRAG_ZOOM_DIRECTION,
     INVERT_SCROLL_ZOOM_DIRECTION,
-    MULTILAYER_ONION,
     LANGUAGE,
     LAYOUT_LOCK,
     DRAW_ON_EMPTY_FRAME_ACTION,