Page 83	Table of Contents	Index	Page 85
	Chapters
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 A, B, C, D, E

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CHAPTER 10. DRAWING OPTIONS

advice of CLIM to the rendering substrate on how to perform the rendering.

=> line-style [Protocol Class]
The protocol class for line styles. If you want to create a new class that behaves like a line
style, it should be a subclass of line-style. Subclasses of line-style must obey the line style
protocol.

=> line-style-p object [Function]
Returns true if object is a line style, otherwise returns false.

=> standard-line-style [Class]
An instantiable class that implements line styles. A subclass of line-style. This is the class
that make-line-style instantiates. Members of this class are immutable.

=> make-line-style &key unit thickness joint-shape cap-shape dashes [Function]
Returns an object of class standard-line-style with the supplied characteristics. The argu-
ments and their default values are described in Section 10.3.1.

10.3.1 Line Style Protocol and Line Style Suboptions

Each of these suboptions has a corresponding reader that can be used to extract a particular
component from a line style. The generic functions decribed below comprise the line style
protocol; all subclasses of line-style must implement methods for these generic functions.

=> :line-unit [Option]
=> line-style-unit line-style [Generic Function]
Gives the unit used for measuring line thickness and dash pattern length for the line style.
Possible values are :normal, :point, or :coordinate. The meaning of these options is:

• :normal - thicknesses and lengths are given in a relative measure in terms of the usual or
  "normal" line thickness. The normal line thickness is the thickness of the "comfortably
  visible thin line", ¹ which is a property of the underlying rendering substrate. This is the
  default.
  
• :point - thicknesses and lengths are given in an absolute measure in terms of printer's
  points (approximately 1=72 of an inch). ²

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¹ In some window systems, the phrase "thinnest visible line" is used. This is not appropriate for CLIM, which
intends to be device independent. (For instance, the thinnest visible line on a 400 d.p.i. laser printer is a function
of the user's viewing distance from the paper.) Another attribute of a "normal" line is that its thickness should
approximately match the stroke thickness of "normal" text, where again the exact measurements are the province
of the rendering engine, not of CLIM.

² This measure was chosen so that CLIM implementors who interface CLIM to an underlying rendering engine
(the window system) may legitimately choose to make it render as 1 pixel on current (1990) display devices.

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Page 83	Table of Contents	Index	Page 85
	Chapters
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 A, B, C, D, E