on-paint

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

The on-paint method, together with the snips' draw methods, must be able to draw the entire state of a buffer. Never paint directly into a buffer'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.

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 approrpiate. Before on-paint returns, it must restore any drawing context settings that it changes.

• (send a-wx:media-buffer on-paint before dc left top right bottom dx dy draw-caret) -> void
      before : boolean
      dc : wx:dc% object
      left : inexact real
      top : inexact real
      right : inexact real
      bottom : inexact real
      dx : inexact real
      dy : inexact real
      draw-caret : small integer

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

  See also invalidate-bitmap-cache.