Refactor motion path logic in VideoEditor for clarity

This commit updates the VideoEditor class to improve the logic for drawing and checking motion paths between tracking points. The comments have been adjusted to clarify the conditions for drawing lines between previous→current and previous→next frames. Additionally, debug statements have been enhanced to provide clearer insights during the snapping process, ensuring better tracking point interactions.

croppa/main.py

@@ -1132,26 +1132,31 @@ class VideoEditor:
         next_frame = min(next_frames)
         return next_frame, self.tracking_points[next_frame]
 
-    def _point_to_line_distance(self, px, py, x1, y1, x2, y2):
-        """Calculate distance from point (px, py) to line segment (x1, y1) to (x2, y2)"""
-        # Vector from line start to end
-        line_dx = x2 - x1
-        line_dy = y2 - y1
-        line_length_sq = line_dx * line_dx + line_dy * line_dy
+    def _point_to_line_distance_and_foot(self, px, py, x1, y1, x2, y2):
+        """Calculate distance from point (px, py) to infinite line (x1, y1) to (x2, y2) and return foot of perpendicular"""
+        # Convert line to general form: Ax + By + C = 0
+        # (y2 - y1)(x - x1) - (x2 - x1)(y - y1) = 0
+        A = y2 - y1
+        B = -(x2 - x1)  # Note the negative sign
+        C = -(A * x1 + B * y1)
         
-        if line_length_sq == 0:
+        # Calculate distance: d = |Ax + By + C| / sqrt(A^2 + B^2)
+        denominator = (A * A + B * B) ** 0.5
+        if denominator == 0:
             # Line is actually a point
-            return ((px - x1) ** 2 + (py - y1) ** 2) ** 0.5
+            distance = ((px - x1) ** 2 + (py - y1) ** 2) ** 0.5
+            return distance, (x1, y1)
         
-        # Parameter t for closest point on line (0 = start, 1 = end)
-        t = max(0, min(1, ((px - x1) * line_dx + (py - y1) * line_dy) / line_length_sq))
+        distance = abs(A * px + B * py + C) / denominator
         
-        # Closest point on line segment
-        closest_x = x1 + t * line_dx
-        closest_y = y1 + t * line_dy
+        # Calculate foot of perpendicular: (xf, yf)
+        # xf = xu - A(Axu + Byu + C)/(A^2 + B^2)
+        # yf = yu - B(Axu + Byu + C)/(A^2 + B^2)
+        numerator = A * px + B * py + C
+        xf = px - A * numerator / (A * A + B * B)
+        yf = py - B * numerator / (A * A + B * B)
         
-        # Distance to closest point
-        return ((px - closest_x) ** 2 + (py - closest_y) ** 2) ** 0.5
+        return distance, (xf, yf)
 
     def advance_frame(self) -> bool:
         """Advance to next frame - handles playback speed and marker looping"""
@@ -2028,35 +2033,42 @@ class VideoEditor:
             prev_result = self._get_previous_tracking_point()
             next_result = self._get_next_tracking_point()
             
-            # Draw motion path if we have both previous and next points
-            if prev_result and next_result:
-                prev_frame, prev_pts = prev_result
-                next_frame, next_pts = next_result
+            # Draw motion path - either previous→current OR previous→next
+            line_to_draw = None
+            if prev_result and self.current_frame in self.tracking_points:
+                # Draw previous→current line (we're on a frame with tracking points)
+                line_to_draw = ("prev_current", prev_result, (self.current_frame, self.tracking_points[self.current_frame]))
+            elif prev_result and next_result:
+                # Draw previous→next line (we're between frames)
+                line_to_draw = ("prev_next", prev_result, next_result)
+            
+            if line_to_draw:
+                line_type, (frame1, pts1), (frame2, pts2) = line_to_draw
                 
                 # Draw lines between corresponding tracking points
-                for i, (prev_rx, prev_ry) in enumerate(prev_pts):
-                    if i < len(next_pts):
-                        next_rx, next_ry = next_pts[i]
-                        prev_sx, prev_sy = self._map_rotated_to_screen(prev_rx, prev_ry)
-                        next_sx, next_sy = self._map_rotated_to_screen(next_rx, next_ry)
+                for i, (px1, py1) in enumerate(pts1):
+                    if i < len(pts2):
+                        px2, py2 = pts2[i]
+                        sx1, sy1 = self._map_rotated_to_screen(px1, py1)
+                        sx2, sy2 = self._map_rotated_to_screen(px2, py2)
                         
                         # Draw motion path line with arrow (thin and transparent)
                         overlay = canvas.copy()
-                        cv2.line(overlay, (prev_sx, prev_sy), (next_sx, next_sy), (255, 255, 0), 1)  # Thin yellow line
+                        cv2.line(overlay, (sx1, sy1), (sx2, sy2), (255, 255, 0), 1)  # Thin yellow line
                         
-                        # Draw arrow head pointing from previous to next
-                        angle = np.arctan2(next_sy - prev_sy, next_sx - prev_sx)
+                        # Draw arrow head pointing from first to second point
+                        angle = np.arctan2(sy2 - sy1, sx2 - sx1)
                         arrow_length = 12
                         arrow_angle = np.pi / 6  # 30 degrees
                         
                         # Calculate arrow head points
-                        arrow_x1 = int(next_sx - arrow_length * np.cos(angle - arrow_angle))
-                        arrow_y1 = int(next_sy - arrow_length * np.sin(angle - arrow_angle))
-                        arrow_x2 = int(next_sx - arrow_length * np.cos(angle + arrow_angle))
-                        arrow_y2 = int(next_sy - arrow_length * np.sin(angle + arrow_angle))
+                        arrow_x1 = int(sx2 - arrow_length * np.cos(angle - arrow_angle))
+                        arrow_y1 = int(sy2 - arrow_length * np.sin(angle - arrow_angle))
+                        arrow_x2 = int(sx2 - arrow_length * np.cos(angle + arrow_angle))
+                        arrow_y2 = int(sy2 - arrow_length * np.sin(angle + arrow_angle))
                         
-                        cv2.line(overlay, (next_sx, next_sy), (arrow_x1, arrow_y1), (255, 255, 0), 1)
-                        cv2.line(overlay, (next_sx, next_sy), (arrow_x2, arrow_y2), (255, 255, 0), 1)
+                        cv2.line(overlay, (sx2, sy2), (arrow_x1, arrow_y1), (255, 255, 0), 1)
+                        cv2.line(overlay, (sx2, sy2), (arrow_x2, arrow_y2), (255, 255, 0), 1)
                         cv2.addWeighted(overlay, 0.3, canvas, 0.7, 0, canvas)  # Very transparent
             
             # Previous tracking point (red) - from the most recent frame with tracking points before current
@@ -2183,7 +2195,7 @@ class VideoEditor:
                     best_snap_point = None
                     
                     # Check all tracking points from all frames for point snapping
-                    for _, points in self.tracking_points.items():
+                    for frame_num, points in self.tracking_points.items():
                         for (px, py) in points:
                             sxp, syp = self._map_rotated_to_screen(px, py)
                             distance = ((sxp - x) ** 2 + (syp - y) ** 2) ** 0.5
@@ -2191,56 +2203,77 @@ class VideoEditor:
                                 best_snap_distance = distance
                                 best_snap_point = (int(px), int(py))
                     
-                    # Check for line snapping between consecutive tracking points
-                    tracking_frames = sorted(self.tracking_points.keys())
-                    for i in range(len(tracking_frames) - 1):
-                        frame1 = tracking_frames[i]
-                        frame2 = tracking_frames[i + 1]
-                        points1 = self.tracking_points[frame1]
-                        points2 = self.tracking_points[frame2]
+                    # Check for line snapping - either previous→next OR previous→current
+                    prev_result = self._get_previous_tracking_point()
+                    next_result = self._get_next_tracking_point()
+                    
+                    print(f"DEBUG: Line snapping - prev_result: {prev_result}, next_result: {next_result}")
+                    
+                    # Determine which line to check: previous→current OR previous→next
+                    line_to_check = None
+                    if prev_result and self.current_frame in self.tracking_points:
+                        # Check previous→current line (we're on a frame with tracking points)
+                        line_to_check = ("prev_current", prev_result, (self.current_frame, self.tracking_points[self.current_frame]))
+                        print(f"DEBUG: Checking prev->current line")
+                    elif prev_result and next_result:
+                        # Check previous→next line (we're between frames)
+                        line_to_check = ("prev_next", prev_result, next_result)
+                        print(f"DEBUG: Checking prev->next line")
+                    
+                    if line_to_check:
+                        line_type, (frame1, pts1), (frame2, pts2) = line_to_check
                         
                         # Check each corresponding pair of points
-                        for j in range(min(len(points1), len(points2))):
-                            px1, py1 = points1[j]
-                            px2, py2 = points2[j]
+                        for j in range(min(len(pts1), len(pts2))):
+                            px1, py1 = pts1[j]
+                            px2, py2 = pts2[j]
                             
                             # Convert to screen coordinates
                             sx1, sy1 = self._map_rotated_to_screen(px1, py1)
                             sx2, sy2 = self._map_rotated_to_screen(px2, py2)
                             
-                            # Calculate distance to line segment
-                            line_distance = self._point_to_line_distance(x, y, sx1, sy1, sx2, sy2)
+                            # Calculate distance to infinite line and foot of perpendicular
+                            line_distance, (foot_x, foot_y) = self._point_to_line_distance_and_foot(x, y, sx1, sy1, sx2, sy2)
+                            
+                            print(f"DEBUG: {line_type} Line {j}: ({sx1},{sy1}) to ({sx2},{sy2}), distance to click ({x},{y}) = {line_distance:.2f}, foot = ({foot_x:.1f}, {foot_y:.1f})")
                             
                             if line_distance <= threshold and line_distance < best_snap_distance:
-                                # Find the closest point on the line segment
-                                line_dx = sx2 - sx1
-                                line_dy = sy2 - sy1
-                                line_length_sq = line_dx * line_dx + line_dy * line_dy
+                                print(f"DEBUG: Line snap found! Distance {line_distance:.2f} <= threshold {threshold}")
                                 
-                                if line_length_sq > 0:
-                                    t = max(0, min(1, ((x - sx1) * line_dx + (y - sy1) * line_dy) / line_length_sq))
-                                    closest_sx = sx1 + t * line_dx
-                                    closest_sy = sy1 + t * line_dy
-                                    
-                                    # Convert back to rotated coordinates
-                                    closest_rx, closest_ry = self._map_screen_to_rotated(int(closest_sx), int(closest_sy))
+                                # Convert foot of perpendicular back to rotated coordinates (no clamping - infinite line)
+                                closest_rx, closest_ry = self._map_screen_to_rotated(int(foot_x), int(foot_y))
                                 
                                 best_snap_distance = line_distance
                                 best_snap_point = (int(closest_rx), int(closest_ry))
+                                print(f"DEBUG: Best line snap point: ({closest_rx}, {closest_ry})")
+                    else:
+                        print(f"DEBUG: No line found for snapping")
                     
                     # Apply the best snap if found
                     if best_snap_point:
+                        print(f"DEBUG: Final best_snap_point: {best_snap_point} (distance: {best_snap_distance:.2f})")
                         self.tracking_points.setdefault(self.current_frame, []).append(best_snap_point)
                         snapped = True
+                    else:
+                        print(f"DEBUG: No snap found, adding new point at: ({rx}, {ry})")
                     
                     # If no snapping, add new point at clicked location
                     if not snapped:
+                        print(f"DEBUG: No snap found, adding new point at: ({rx}, {ry})")
+                        print(f"DEBUG: Click was at screen coords: ({x}, {y})")
+                        print(f"DEBUG: Converted to rotated coords: ({rx}, {ry})")
+                        # Verify the conversion
+                        verify_sx, verify_sy = self._map_rotated_to_screen(rx, ry)
+                        print(f"DEBUG: Verification - rotated ({rx}, {ry}) -> screen ({verify_sx}, {verify_sy})")
                         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()
                 
+                # Force immediate display update to recalculate previous/next points and arrows
+                self.display_current_frame()
+
         # Handle scroll wheel: Ctrl+scroll -> zoom; plain scroll -> seek ±1 frame (independent of multiplier)
         if event == cv2.EVENT_MOUSEWHEEL:
             if flags & cv2.EVENT_FLAG_CTRLKEY: