Created
November 9, 2023 12:50
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Finds the intersection point between two grease pencil strokes in Blender
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| import bpy | |
| from math import pi, sin, cos | |
| def ellipse(gp_frame, center, radius_x, radius_z, num_points): | |
| gp_stroke = gp_frame.strokes.new() | |
| gp_stroke.line_width = 30 | |
| gp_stroke.use_cyclic = True | |
| gp_stroke.points.add(count=num_points) | |
| step = (2 * pi) / num_points | |
| for i in range(num_points): | |
| angle = i * step | |
| x = center[0] + (radius_x * cos(angle)) | |
| y = 0 | |
| z = center[2] + (radius_z* sin(angle)) | |
| gp_stroke.points[i].co = (x, y, z) | |
| return gp_stroke | |
| def find_line_intersection(a1_pos, a2_pos, b1_pos, b2_pos, bounded=True): | |
| a1x, a1z = a1_pos[0], a1_pos[2] | |
| a2x, a2z = a2_pos[0], a2_pos[2] | |
| b1x, b1z = b1_pos[0], b1_pos[2] | |
| b2x, b2z = b2_pos[0], b2_pos[2] | |
| denom = (a1x-a2x)*(b1z-b2z)-(a1z-a2z)*(b1x-b2x) | |
| if denom == 0: | |
| return None | |
| numerator_x = ((b1x-b2x)*(a1x*a2z-a1z*a2x)-(a1x-a2x)*(b1x*b2z-b1z*b2x)) | |
| numerator_z = ((b1z-b2z)*(a1x*a2z-a1z*a2x)-(a1z-a2z)*(b1x*b2z-b1z*b2x)) | |
| xi = numerator_x / denom | |
| zi = numerator_z / denom | |
| if bounded: | |
| if xi < min(a1x, a2x) or xi > max(a1x, a2x): | |
| return None | |
| if zi < min(a1z, a2z) or zi > max(a1z, a2z): | |
| return None | |
| if xi < min(b1x, b2x) or xi > max(b1x, b2x): | |
| return None | |
| if zi < min(b1z, b2z) or zi > max(b1z, b2z): | |
| return None | |
| return (xi, 0, zi) | |
| def find_stroke_intersections(stroke1, stroke2, bounded=True): | |
| intersections = [] | |
| for i in range(len(stroke1.points)): | |
| p1 = stroke1.points[i].co | |
| if i == (len(stroke1.points)-1): | |
| if stroke1.use_cyclic: | |
| p2 = stroke1.points[0].co | |
| else: | |
| break | |
| else: | |
| p2 = stroke1.points[i+1].co | |
| for j in range(len(stroke2.points)): | |
| p3 = stroke2.points[j].co | |
| if j == (len(stroke2.points)-1): | |
| if stroke2.use_cyclic: | |
| p4 = stroke2.points[0].co | |
| else: | |
| break | |
| else: | |
| p4 = stroke2.points[j+1].co | |
| intersection = find_line_intersection(p1, p2, p3, p4, bounded) | |
| if intersection: | |
| intersections.append(intersection) | |
| return intersections | |
| sel_obj = None | |
| sel_objs = bpy.context.selected_objects | |
| if sel_objs: | |
| sel_obj = sel_objs[0] | |
| if sel_obj is not None and sel_obj.type == 'GPENCIL': | |
| gpencil = sel_obj.data | |
| gp_layer = gpencil.layers.active | |
| gp_frame = gp_layer.frames[0] | |
| stroke1, stroke2 = gp_frame.strokes[0], gp_frame.strokes[1] | |
| # a1 = stroke1.points[0].co | |
| # a2 = stroke1.points[1].co | |
| # b1 = stroke2.points[0].co | |
| # b2 = stroke2.points[1].co | |
| intersections = find_stroke_intersections(stroke1, stroke2, True) | |
| for intersection in intersections: | |
| ellipse(gp_frame, intersection, 0.1, 0.1, 24) | |
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