on-paint in text:delegate-mixin

Provides a way to add arbitrary graphics to an editor's display. This method is called just before and just after every painting of the editor.

The on-paint method, together with the snips' draw methods, must be able to draw the entire state of an editor. Never paint directly into an editor's display canvas except from within on-paint or draw. Instead, put all extra drawing code within on-paint and call invalidate-bitmap-cache when part of the display needs to be repainted.

If an on-paint method uses cached location information, then the cached information should be recomputed in response to a call of invalidate-bitmap-cache.

The on-paint method must not make any assumptions about the state of the drawing context (e.g., the current pen), except that the clipping region is already set to something appropriate. Before on-paint returns, it must restore any drawing context settings that it changes.

The editor is internally locked for writing and reflowing during a call to this method (see also Locks).

• (send a-text:delegate-mixin on-paint before? dc left top right bottom dx dy draw-caret) -> void
     before? : boolean
     dc : dc<%> object
     left : real number
     top : real number
     right : real number
     bottom : real number
     dx : real number
     dy : real number
     draw-caret : symbol in '(no-caret show-inactive-caret show-caret)

  The before? argument is #t when the method is called just before a painting the contents of the editor or #f when it is called after painting. The left, top, right, and bottom arguments specify which region of the editor is being repainted, in editor coordinates. To get the coordinates for dc, offset editor coordinates by adding (dx, dy). See Caret for information about draw-caret.

  See also invalidate-bitmap-cache.

  Draws a blue region in the delegatee editor that shows where the visible region of the delegate editor is.