Refactor point-to-line distance calculation in VideoEditor

This commit refines the distance calculation method in the VideoEditor class by introducing a new function, _point_to_line_distance_and_foot, which computes the distance from a point to an infinite line and returns the foot of the perpendicular. The snapping logic has been updated to utilize this new method, enhancing the accuracy of line snapping between tracking points. Additionally, debug statements have been added to assist in tracking the snapping process and verifying point conversions.

croppa/main.py

@@ -510,7 +510,7 @@ class VideoEditor:
     CROP_SIZE_STEP = 15  # pixels to expand/contract crop
 
     # Motion tracking settings
-    TRACKING_POINT_THRESHOLD = 10  # pixels for delete/snap radius
+    TRACKING_POINT_THRESHOLD = 20  # pixels for delete/snap radius
 
     # Seek frame counts
     SEEK_FRAMES_CTRL = 60  # Ctrl modifier: 60 frames
@@ -1132,6 +1132,32 @@ class VideoEditor:
         next_frame = min(next_frames)
         return next_frame, self.tracking_points[next_frame]
 
+    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)
+        
+        # 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
+            distance = ((px - x1) ** 2 + (py - y1) ** 2) ** 0.5
+            return distance, (x1, y1)
+        
+        distance = abs(A * px + B * py + C) / denominator
+        
+        # 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)
+        
+        return distance, (xf, yf)
+
     def advance_frame(self) -> bool:
         """Advance to next frame - handles playback speed and marker looping"""
         if not self.is_playing:
@@ -2155,23 +2181,91 @@ class VideoEditor:
                             removed = True
                             break
                 
-                # If not removed, check for snapping to nearby points from other frames
+                # If not removed, check for snapping to nearby points or lines from other frames
                 if not removed:
                     snapped = False
-                    # Check all tracking points from all frames for snapping
+                    best_snap_distance = float('inf')
-                    for _, points in self.tracking_points.items():
+                    best_snap_point = None
+                    
+                    # Check all tracking points from all frames for point 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:
+                            distance = ((sxp - x) ** 2 + (syp - y) ** 2) ** 0.5
-                                # Snap to this existing point
+                            if distance <= threshold and distance < best_snap_distance:
-                                self.tracking_points.setdefault(self.current_frame, []).append((int(px), int(py)))
+                                best_snap_distance = distance
-                                snapped = True
+                                best_snap_point = (int(px), int(py))
-                                break
+                    
-                        if snapped:
+                    # Check for line snapping between previous and next tracking points (the actual cyan arrows)
-                            break
+                    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}")
+                    
+                    if prev_result and next_result:
+                        prev_frame, prev_pts = prev_result
+                        next_frame, next_pts = next_result
+                        
+                        print(f"DEBUG: Checking line between prev frame {prev_frame} and next frame {next_frame}")
+                        
+                        # Check each corresponding pair of points between previous and next
+                        for j in range(min(len(prev_pts), len(next_pts))):
+                            px1, py1 = prev_pts[j]
+                            px2, py2 = next_pts[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 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 {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:
+                                print(f"DEBUG: Line snap found! Distance {line_distance:.2f} <= threshold {threshold}")
+                                
+                                # Clamp the foot to the line segment
+                                # Calculate parameter t for the foot point
+                                line_dx = sx2 - sx1
+                                line_dy = sy2 - sy1
+                                line_length_sq = line_dx * line_dx + line_dy * line_dy
+                                
+                                if line_length_sq > 0:
+                                    t = ((foot_x - sx1) * line_dx + (foot_y - sy1) * line_dy) / line_length_sq
+                                    t = max(0, min(1, t))  # Clamp to [0, 1]
+                                    
+                                    # Calculate clamped foot point
+                                    clamped_foot_x = sx1 + t * line_dx
+                                    clamped_foot_y = sy1 + t * line_dy
+                                    
+                                    print(f"DEBUG: Clamped foot from ({foot_x:.1f}, {foot_y:.1f}) to ({clamped_foot_x:.1f}, {clamped_foot_y:.1f})")
+                                    
+                                    # Convert clamped foot back to rotated coordinates
+                                    closest_rx, closest_ry = self._map_screen_to_rotated(int(clamped_foot_x), int(clamped_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 prev/next points found for line 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")
                 

croppa/spec.md

@@ -57,8 +57,9 @@ 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 existing point**: Remove tracking point (within 10px)
-- **Right-click near existing point**: Snap to existing point from any frame (within 50px radius)
+- **Right-click near existing point**: Snap to existing point from any frame (within 10px radius)
+- **Right-click near motion path**: Snap to closest point on yellow arrow line between tracking points (within 10px radius)
 - **v**: Toggle motion tracking on/off
 - **V**: Clear all tracking points
 - **Blue cross**: Shows computed tracking position