- canvas->rend_desc().set_tl(Vector(-4,2.25));
- canvas->rend_desc().set_br(Vector(4,-2.25));
+ // The top left and botton right positions are expressed in units
+ // Original convention is that 1 unit = 60 pixels
+ canvas->rend_desc().set_tl(Vector(-(preferred_x_size/60.0)/2.0,(preferred_y_size/60.0)/2.0));
+ canvas->rend_desc().set_br(Vector((preferred_x_size/60.0)/2.0,-(preferred_y_size/60.0)/2.0));