gistfile1.cpp

// Tests each segment for a hit. All calculations are done in screen space pixel coordinates
bool CollisionPath::hitTest(const ViewportPosition &selection_position) const
{
	const Vector2 &mouse_pixel_pos = selection_position.getPixelPosition();
	const Viewport &viewport = selection_position.getViewport();
	const Camera &camera = viewport.getCamera();
	const WorldLayer &layer = *getLayer();

	for(auto iter = anchors.begin(); iter != anchors.end()-1; ++iter) {
		const Vector2 &segment_begin = 
			camera.projectToPixels(viewport, *iter, layer.getDistance());
		const Vector2 &segment_end = 
			camera.projectToPixels(viewport, *(iter+1), layer.getDistance());

		// Calculate nearest position on segment from mouse
		const Vector2 begin_to_end_v = (segment_end - segment_begin);
		const float segment_length = begin_to_end_v.length();
		const Vector2 segment_normal = begin_to_end_v / segment_length;
		const float t = segment_normal * (mouse_pixel_pos - segment_begin);
		const Vector2 nearest_pos = segment_begin + (segment_normal * t);

		// Check if point lies outside of segment
		if(t < 0.0f || t > segment_length) {
			continue;
		}

		// Calculate layer distance from mouse position
		const Vector2 mouse_to_nearest_pos_v = nearest_pos - mouse_pixel_pos;
		const float mouse_to_segment_distance = mouse_to_nearest_pos_v.length();

		if(mouse_to_segment_distance < 3.0f) {
			return true;
		}
	}	

	return false;
}