Masks as Photoshop's: the button reveals the selection, Alt-click shows a mask alone (13.12)

src/Document/LayerMask+Alone.cpp

@@ -0,0 +1,21 @@
+#include "Document/EditorSession.h"
+
+// Swift's mask shown alone, an Alt-click on its thumbnail.
+std::optional<ImageLayer> EditorSession::maskAloneLayer() const
+{
+    const std::optional<ImageLayer> layer = activeLayer();
+    if (!m_viewsMaskAlone || !m_isMaskSelected || !layer || !layer->mask)
+        return std::nullopt;
+    return layer;
+}
+
+void EditorSession::toggleMaskAlone(QUuid id)
+{
+    const std::optional<ImageLayer> shown = maskAloneLayer();
+    const bool showing = shown && shown->id == id;
+    selectLayerTarget(id, true);
+    if (m_activeLayerID != id || !m_isMaskSelected)
+        return;
+    m_viewsMaskAlone = !showing;
+    notify();
+}