feat: allows dragging to move around the canvas

labelme/app.py

@@ -527,7 +527,7 @@ def __init__(
         )
         zoomOrg = action(
             self.tr("&Original size"),
-            functools.partial(self.setZoom, 100),
+            self.setOriginalSize,
             shortcuts["zoom_to_original"],
             "zoom",
             self.tr("Zoom to original size"),
@@ -1582,8 +1582,10 @@ def setScroll(self, orientation, value):
         self.scroll_values[orientation][self.filename] = value
 
     def setZoom(self, value):
+        self.actions.zoomOrg.setChecked(False)
         self.actions.fitWidth.setChecked(False)
         self.actions.fitWindow.setChecked(False)
+        self.canvas.setEnableDragBuffer(value > 100)
         self.zoomMode = self.MANUAL_ZOOM
         self.zoomWidget.setValue(value)
         self.zoom_values[self.filename] = (self.zoomMode, value)
@@ -1602,6 +1604,7 @@ def zoomRequest(self, delta, pos):
         if delta < 0:
             units = 0.9
         self.addZoom(units)
+        self.canvas.adjustSize()
 
         canvas_width_new = self.canvas.width()
         if canvas_width_old != canvas_width_new:
@@ -1619,16 +1622,24 @@ def zoomRequest(self, delta, pos):
                 self.scrollBars[Qt.Vertical].value() + y_shift,
             )
 
+    def setOriginalSize(self, value=True):
+        if value:
+            self.actions.zoomOrg.setChecked(False)
+        self.canvas.setEnableDragBuffer(False)
+        self.setZoom(100)
+
     def setFitWindow(self, value=True):
         if value:
             self.actions.fitWidth.setChecked(False)
         self.zoomMode = self.FIT_WINDOW if value else self.MANUAL_ZOOM
+        self.canvas.setEnableDragBuffer(False)
         self.adjustScale()
 
     def setFitWidth(self, value=True):
         if value:
             self.actions.fitWindow.setChecked(False)
         self.zoomMode = self.FIT_WIDTH if value else self.MANUAL_ZOOM
+        self.canvas.setEnableDragBuffer(False)
         self.adjustScale()
 
     def enableKeepPrevScale(self, enabled):

labelme/widgets/canvas.py

@@ -100,6 +100,7 @@ def __init__(self, *args, **kwargs):
         self.line = Shape()
         self.prevPoint = QPointF()
         self.prevMovePoint = QPointF()
+        self.prevDragPoint = QPointF()
         self.offsets = QPointF(), QPointF()
         self.scale = 1.0
         self.pixmap = QtGui.QPixmap()
@@ -117,6 +118,8 @@ def __init__(self, *args, **kwargs):
         self.hShapeIsSelected = False
         self._painter = QtGui.QPainter()
         self._cursor = CURSOR_DEFAULT
+        self.drag = False
+        self.enableDragBuffer = False
         # Menus:
         # 0: right-click without selection and dragging of shapes
         # 1: right-click with selection and dragging of shapes
@@ -308,6 +311,14 @@ def mouseMoveEvent(self, ev):
 
         is_shift_pressed = ev.modifiers() & Qt.ShiftModifier
 
+        # Drag to move canvas
+        if self.drag:
+            self.overrideCursor(CURSOR_GRAB)
+            delta = pos - self.prevDragPoint
+
+            self.scrollRequest.emit(int(delta.x()), Qt.Horizontal)
+            self.scrollRequest.emit(int(delta.y()), Qt.Vertical)
+
         # Polygon drawing.
         if self.drawing():
             if self.createMode in ["ai_polygon", "ai_mask"]:
@@ -563,9 +574,13 @@ def mousePressEvent(self, ev):
                 self.selectShapePoint(pos, multiple_selection_mode=group_mode)
                 self.repaint()
             self.prevPoint = pos
-        self._update_status()
+        elif ev.button() == Qt.MiddleButton:
+            self.overrideCursor(CURSOR_GRAB)
+            self.prevDragPoint = pos
+            self.drag = True
 
     def mouseReleaseEvent(self, ev):
+        pos: QPointF = self.transformPos(ev.localPos())
         if ev.button() == Qt.RightButton:
             menu = self.menus[len(self.selectedShapesCopy) > 0]
             self.restoreCursor()
@@ -583,6 +598,8 @@ def mouseReleaseEvent(self, ev):
                     self.selectionChanged.emit(
                         [x for x in self.selectedShapes if x != self.hShape]
                     )
+        elif ev.button() == Qt.MiddleButton:
+            self.drag = False
 
         if self.movingShape and self.hShape:
             index = self.shapes.index(self.hShape)
@@ -841,6 +858,9 @@ def transformPos(self, point: QPointF) -> QPointF:
         """Convert from widget-logical coordinates to painter-logical ones."""
         return point / self.scale - self.offsetToCenter()
 
+    def setEnableDragBuffer(self, enabled: bool):
+        self.enableDragBuffer = enabled
+
     def offsetToCenter(self) -> QPointF:
         s = self.scale
         area = super().size()
@@ -941,8 +961,14 @@ def sizeHint(self):
 
     def minimumSizeHint(self):
         if self.pixmap:
-            return self.scale * self.pixmap.size()
-        return super().minimumSizeHint()
+            min_size = self.scale * self.pixmap.size()
+            if self.enableDragBuffer:
+                # When drag buffer should be enabled, add a bit of buffer around the image
+                # This lets dragging the image around have a bit of give on the edges
+                min_size = 1.167 * min_size
+
+            return min_size
+        return super(Canvas, self).minimumSizeHint()
 
     def wheelEvent(self, ev: QtGui.QWheelEvent) -> None:
         mods: Qt.KeyboardModifiers = ev.modifiers()