feat(iv): Implement files drag and drop into an iv window (#4774)

Drag and drop of files. Tested on my own Mac and it seem to work just
fine.

Fixes #4771

---------

Signed-off-by: Aleksandr Motsjonov <soswow@gmail.com>

Author: soswow

src/iv/imageviewer.cpp

@@ -152,6 +152,13 @@ ImageViewer::ImageViewer(bool use_ocio, const std::string& image_color_space,
 
     setWindowTitle(tr("Image Viewer"));
     resize(m_default_width, m_default_height);
+
+    setAcceptDrops(true);
+    // Disable drag and drop on child widgets
+    for (QWidget* child : findChildren<QWidget*>()) {
+        child->setAcceptDrops(false);
+    }
+
     //    setSizePolicy (QSizePolicy::Ignored, QSizePolicy::Ignored);
 
     setAttribute(Qt::WA_DeleteOnClose);
@@ -173,6 +180,30 @@ ImageViewer::closeEvent(QCloseEvent*)
     writeSettings();
 }
 
+void
+ImageViewer::dragEnterEvent(QDragEnterEvent* event)
+{
+    if (event->mimeData()->hasUrls())
+        event->acceptProposedAction();
+}
+
+void
+ImageViewer::dropEvent(QDropEvent* event)
+{
+    const QMimeData* mimeData = event->mimeData();
+    if (mimeData->hasUrls()) {
+        size_t old_size = m_images.size();
+        for (const QUrl& url : mimeData->urls()) {
+            QString filePath = url.toLocalFile();
+            add_image(filePath.toStdString());
+        }
+        // Switch to the first newly added image
+        if (m_images.size() > old_size) {
+            current_image(old_size);
+        }
+    }
+}
+
 
 
 void

src/iv/imageviewer.h

@@ -25,6 +25,7 @@
 #include <QCheckBox>
 #include <QDialog>
 #include <QMainWindow>
+#include <QMimeData>
 
 #if OIIO_QT_MAJOR < 6
 #    include <QGLWidget>
@@ -338,6 +339,8 @@ private slots:
     void keyPressEvent(QKeyEvent* event) override;
     void resizeEvent(QResizeEvent* event) override;
     void closeEvent(QCloseEvent* event) override;
+    void dragEnterEvent(QDragEnterEvent* event) override;
+    void dropEvent(QDropEvent* event) override;
 
     QTimer* slideTimer;     ///< Timer to use for slide show mode
     long slideDuration_ms;  ///< Slide show mode duration (in ms)