+ float canvas_x0 = (x0 - half_track_w) * projector_z + projector_x;
+ float canvas_y0 = (y0 - half_track_h) * projector_z + projector_y;
+ float canvas_x1 = (x1 - half_track_w) * projector_z + projector_x;
+ float canvas_y1 = (y1 - half_track_h) * projector_z + projector_y;
+ float canvas_x2 = (x2 - half_track_w) * projector_z + projector_x;
+ float canvas_y2 = (y2 - half_track_h) * projector_z + projector_y;
+ float canvas_x3 = (x3 - half_track_w) * projector_z + projector_x;
+ float canvas_y3 = (y3 - half_track_h) * projector_z + projector_y;