June 23, 2010
Notes on Clipping and translation in MIDP
To make less mistakes in MIDP graphics it's important to know how is it work. Actually, MIDP docs and books I've read describes clipping and translation very superficially.
The notes 1 and 3 described below was some a surprise for me.
1. Graphics calculates and stores clipping: a) on each clipRect() call; b) in absolute (screen) coords.
Example:
you could expect nothing on screen, but it's wrong.
2. (obvious) Graphics' clipRect() offset is expected in current translated coords. (see example below in (3))
3. Graphics always have clipping enabled (by default is's equal to the whole paintable area size, different depending on fullscreen mode).
Example:
The notes 1 and 3 described below was some a surprise for me.
1. Graphics calculates and stores clipping: a) on each clipRect() call; b) in absolute (screen) coords.
Example:
clipRect(0,0,50,25)rect is painted with height 25
translate(0,-25)
fillRect(0,0,50,50)
you could expect nothing on screen, but it's wrong.
2. (obvious) Graphics' clipRect() offset is expected in current translated coords. (see example below in (3))
3. Graphics always have clipping enabled (by default is's equal to the whole paintable area size, different depending on fullscreen mode).
Example:
you get nothing painted, because on clipRect() call clipping was intersected with default clipping -> become (w=0,h=0) which is stored. On second translate call clipping area is not recalculated.
translate(0,-25)
clipRect(0,25)
translate(0,25)
fillRect(0,0,50,50)
Labels: graphics, j2me, java, midp, programming
