[gnome-shell/gbsneto/icon-grid-dnd: 5/13] allView: Switch pages when dragging above or below the grid

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 553de0ac90200d0a34e764e78b3b6d23ca5b06c5
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Fri Jun 28 20:48:22 2019 -0300

    allView: Switch pages when dragging above or below the grid
    
    This is necessary for being able to drag application icons
    to folders in different pages.
    
    Add a drag motion handler to AllView and handle overshoots
    when dragging. Only handle it when dragging from AllView.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/603

 js/ui/appDisplay.js | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
---
diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index b1aeafa93..c7029a739 100644
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -334,6 +334,9 @@ var AllView = class AllView extends BaseAppView {
             Main.queueDeferredWork(this._redisplayWorkId);
         });
 
+        Main.overview.connect('item-drag-begin', this._onDragBegin.bind(this));
+        Main.overview.connect('item-drag-end', this._onDragEnd.bind(this));
+
         this._nEventBlockerInhibits = 0;
     }
 
@@ -649,6 +652,59 @@ var AllView = class AllView extends BaseAppView {
             this.folderIcons[i].adaptToSize(availWidth, availHeight);
     }
 
+    _handleDragOvershoot(dragEvent) {
+        let [gridX, gridY] = this.actor.get_transformed_position();
+        let [gridWidth, gridHeight] = this.actor.get_transformed_size();
+        let gridBottom = gridY + gridHeight;
+
+        // Within the grid boundaries - cancel any existing scrolling
+        if (dragEvent.y > gridY && dragEvent.y < gridBottom) {
+            if (Tweener.isTweening(this._adjustment))
+                Tweener.removeTweens(this._adjustment);
+            return;
+        }
+
+        // Moving above the grid
+        let currentY = this._adjustment.value;
+        if (dragEvent.y <= gridY && currentY > 0) {
+            this.goToPage(this._grid.currentPage - 1);
+            return;
+        }
+
+        // Moving below the grid
+        let maxY = this._adjustment.upper - this._adjustment.page_size;
+        if (dragEvent.y >= gridBottom && currentY < maxY) {
+            this.goToPage(this._grid.currentPage + 1);
+            return;
+        }
+    }
+
+    _onDragBegin() {
+        this._dragMonitor = {
+            dragMotion: this._onDragMotion.bind(this)
+        };
+        DND.addDragMonitor(this._dragMonitor);
+    }
+
+    _onDragMotion(dragEvent) {
+        let appIcon = dragEvent.source;
+
+        // Handle the drag overshoot. When dragging to above the
+        // icon grid, move to the page above; when dragging below,
+        // move to the page below.
+        if (appIcon.parentView == this)
+            this._handleDragOvershoot(dragEvent);
+
+        return DND.DragMotionResult.CONTINUE;
+    }
+
+    _onDragEnd() {
+        if (this._dragMonitor) {
+            DND.removeDragMonitor(this._dragMonitor);
+            this._dragMonitor = null;
+        }
+    }
+
     inhibitEventBlocker() {
         this._nEventBlockerInhibits++;
         this._eventBlocker.visible = this._nEventBlockerInhibits == 0;