OmaPhoto 1.0.0: the Linux port of Compositor

A layered image editor for Linux and Omarchy, ported from Compositor
(github.com/robbietilton/Compositor), whose Swift source is its
specification. It reads and writes Compositor's .comp projects.

Packages for Ubuntu, Fedora and Arch come from the release workflow;
scripts/install/ holds one install script per distribution family,
and flake.nix serves NixOS.

Co-Authored-By: Claude <noreply@anthropic.com>

src/UI/BlendModePicker.cpp

@@ -0,0 +1,65 @@
+#include "UI/BlendModePicker.h"
+
+BlendModePicker::BlendModePicker(EditorSession &session, QWidget *parent) : QComboBox(parent), m_session(session)
+{
+    setAccessibleName(QStringLiteral("Blend mode"));
+    setObjectName(QStringLiteral("blendMode"));
+    for (const LayerBlendMode mode : allLayerBlendModes)
+        addItem(rawValue(mode));
+    connect(this, &QComboBox::highlighted, this, &BlendModePicker::highlight);
+    connect(this, &QComboBox::activated, this, &BlendModePicker::choose);
+    connect(&m_session, &EditorSession::changed, this, &BlendModePicker::synchronize);
+    synchronize();
+}
+
+void BlendModePicker::showPopup()
+{
+    m_tracking = true;
+    m_layerID = m_session.activeLayerID();
+    m_highlighted = std::nullopt;
+    QComboBox::showPopup();
+}
+
+void BlendModePicker::hidePopup()
+{
+    QComboBox::hidePopup();
+    m_tracking = false;
+    // A click closes the menu, then chooses: clear after.
+    QMetaObject::invokeMethod(this, [this] {
+        m_session.previewBlendMode(std::nullopt, std::nullopt);
+        m_layerID = std::nullopt;
+        m_highlighted = std::nullopt;
+    }, Qt::QueuedConnection);
+}
+
+void BlendModePicker::synchronize()
+{
+    setEnabled(m_session.canEditAppearance());
+    if (m_tracking)
+        return;
+    const std::optional<ImageLayer> active = m_session.activeLayer();
+    setCurrentText(rawValue(active ? active->blendMode : LayerBlendMode::normal));
+}
+
+void BlendModePicker::highlight(int index)
+{
+    const std::optional<LayerBlendMode> mode = layerBlendMode(itemText(index));
+    if (mode)
+        m_highlighted = mode;
+    m_session.previewBlendMode(mode, m_layerID);
+}
+
+void BlendModePicker::choose(int index)
+{
+    // The layer the menu opened on; closed, the active one.
+    const std::optional<QUuid> target = m_layerID ? m_layerID : m_session.activeLayerID();
+    const std::optional<LayerBlendMode> mode = m_highlighted ? m_highlighted : layerBlendMode(itemText(index));
+    m_highlighted = std::nullopt;
+    m_layerID = std::nullopt;
+    if (!mode || m_session.activeLayerID() != target) {
+        synchronize();
+        return;
+    }
+    m_session.setLayerBlendMode(*mode);
+    setCurrentText(rawValue(*mode));
+}