13.3 Graphics state

The graphics-state object associated with each port holds values for parameters such as foreground, background, operation, thickness, scale-thickness, mask and font which affect graphics ports drawing to that port.

The full set of parameters is described under graphics-state.

13.3.1 Setting the graphics state

The graphics state values associated with a drawing function call are set by one of three mechanisms.

1. Enumeration in the drawing function call. For example:

   (draw-line port 1 1 100 100  
              :thickness 10
              :scale-thickness nil
              :foreground :red)
   

2. Bound using macros such as with-graphics-state. For example:

   (with-graphics-state (port :thickness 10
                              :scale-thickness nil
                              :foreground :red)
     (draw-line port 1 1 100 100)
     (draw-rectangle port 2 2 40 50 :filled t))
   

   For common cases of locally changing the transform in the graphics state, there are specific macros:

   • with-graphics-transform just changes the transform like with-graphics-state with :transform.
   • with-graphics-transform-reset allows you to ignore surrounding transformations.
   • with-graphics-translation, with-graphics-post-translation, with-graphics-scale and with-graphics-rotation perform commonly-used transformations.
   • with-graphics-mask affects specifically the masking slots.
3. Set by the set-graphics-state function. For example:

   (set-graphics-state port :thickness 10
                       :scale-thickness nil
                       :foreground :red)
   

The first two mechanisms change the graphics state temporarily. The last one changes it permanently in port, effectively altering the "default" state.