13.1 The :ink Drawing Option

The :ink drawing option, used with the drawing functions described in Chapter 12, can take as its value: [annotate]

More exactly, an ink can be any member of the class design. For now you may think of a design as a possibly translucent color. More general designs are described in Chapter 14. [annotate]

The drawing functions work by selecting a region of the drawing plane and painting it with color. The region to be painted is the intersection of the shape specified by the drawing function and the :clipping-region drawing option, which is then transformed by the :transformation drawing option. The :ink drawing option is a design that specifies a new arrangement of colors (and opacities) in this region of the medium's drawing plane. Any viewports or dataports attached to this drawing plane are updated accordingly. The :ink drawing option is never affected by the :transformation drawing option nor by the medium's transformation; this ensures that stipple patterns on adjacent sheets join seamlessly. [annotate]

Minor issue: The description of how the clipping region and transformations contribute isn't good enough. It is true if there are no other transformations and clipping regions present, and both are specified in the current drawing operation. But it doesn't say what happens if things are nested. I'm not sure it needs to. Rather, I think it should just say that the the region is clipped by the current clipping region in effect, then transformed by the current transform in effect, and that the rules for these are discussed in the drawing options section. --- DCPL [annotate]

Drawing consists conceptually of the following sequence of operations, performed in parallel at every point in the drawing plane. Of course, the actual implementation does not involve an infinite (or large parallel) computation. [annotate]

  1. The design specifies a color and an opacity at the point. These can depend on the drawing plane's current color and opacity, on the medium's foreground color, and on the medium's background color. [annotate]
  2. The color blending function is applied to the design's color and opacity and the drawing plane's color and opacity, returning a new color and opacity for the point. [annotate]
  3. The drawing plane's color and opacity at that point are set to the new color and opacity. [annotate]