Implement snapping functionality for tracking points in VideoEditor

This commit enhances the VideoEditor class by adding a snapping feature that allows users to snap new tracking points to existing points from any frame within a 50px radius. The logic first checks for the removal of existing points before determining if a new point should be added or if it should snap to a nearby point. The specification has been updated to reflect this new snapping behavior, improving the precision of motion tracking.

croppa/main.py

@@ -2227,6 +2227,8 @@ class VideoEditor:
                 rx, ry = self._map_screen_to_rotated(x, y)
                 threshold = 50
                 removed = False
+                
+                # First check for removal of existing points on current frame
                 if self.current_frame in self.tracking_points:
                     pts_screen = []
                     for idx, (px, py) in enumerate(self.tracking_points[self.current_frame]):
@@ -2240,9 +2242,27 @@ class VideoEditor:
                             # self.show_feedback_message("Tracking point removed")
                             removed = True
                             break
+                
+                # If not removed, check for snapping to nearby points from other frames
                 if not removed:
+                    snapped = False
+                    # Check all tracking points from all frames for snapping
+                    for frame_num, points in self.tracking_points.items():
+                        for (px, py) in points:
+                            sxp, syp = self._map_rotated_to_screen(px, py)
+                            if (sxp - x) ** 2 + (syp - y) ** 2 <= threshold ** 2:
+                                # Snap to this existing point
+                                self.tracking_points.setdefault(self.current_frame, []).append((int(px), int(py)))
+                                snapped = True
+                                break
+                        if snapped:
+                            break
+                    
+                    # If no snapping, add new point at clicked location
+                    if not snapped:
                         self.tracking_points.setdefault(self.current_frame, []).append((int(rx), int(ry)))
                         # self.show_feedback_message("Tracking point added")
+                
                 self.clear_transformation_cache()
                 self.save_state()
 

croppa/spec.md

@@ -58,6 +58,7 @@ Be careful to save and load settings when navigating this way
 ### Motion Tracking
 - **Right-click**: Add tracking point (green circle with white border)
 - **Right-click existing point**: Remove tracking point (within 50px)
+- **Right-click near existing point**: Snap to existing point from any frame (within 50px radius)
 - **v**: Toggle motion tracking on/off
 - **V**: Clear all tracking points
 - **Blue cross**: Shows computed tracking position