[ab] Feature suggestion -- support subsurface blitting

[Anthony Fairchild]

Hello again,

I finally got back to working on my lispy jigsaw puzzle game and I've made a
few changes to the code to clean things up and make it more manageable.  In
the first implementation I made a new surface for every puzzle piece and
rotation.  This generated a very large number of surfaces.  The cleaner
solution involves using a single surface containing an image array of each
puzzle piece.  See this link for an example:
http://img395.imageshack.us/my.php?image=leaveshb1.png

To blit the images on the screen I have to use SDL-BASE::BLIT-SURFACE
because it take a source and destination rectangle.  I created my own
blitting function to wrap the low level foreign pointer stuff, and it
initially looked like this:

(defun blit (src dst sx sy dx dy w h)
  (sdl-base::blit-surface (sdl:fp src) (sdl:fp dst)
                          (sdl:fp (sdl:rectangle :x sx :y sy
                                                 :w w :h h))
                          (sdl:fp (sdl:rectangle
                                   :x dx :y dy
                                   :w w :h h))))

But this function is very slow because calling SDL:RECTANGLE conses a lot,
so much that the GC was kicking in during my paints!.  To fix it I had to
create some global variables to hold reusable rectangles.  Here's the ugly
fast code:

;; Use these globals to hold reusable rectangles for BLIT-FAST to
;; avoid consing.  This is ugly and not thread safe. Is there a better
;; way to do this??
(defparameter *blit-r-src* (sdl:rectangle :x 0 :y 0 :w 0 :h 0))
(defparameter *blit-r-dst* (sdl:rectangle :x 0 :y 0 :w 0 :h 0))

(defun blit-fast (src dst sx sy dx dy w h)
  (setf (sdl:x *blit-r-src*) sx)(setf (sdl:y *blit-r-src*) sy)
  (setf (sdl:width *blit-r-src*) w)(setf (sdl:height *blit-r-src*) h)
  (setf (sdl:x *blit-r-dst*) dx)(setf (sdl:y *blit-r-dst*) dy)
  (setf (sdl:width *blit-r-dst*) w)(setf (sdl:height *blit-r-dst*) h)
  (sdl-base::blit-surface (sdl:fp src) (sdl:fp dst)
                               (sdl:fp *blit-r-src*)
                               (sdl:fp *blit-r-dst*)))

It seems like there is a better way of doing that.  Any suggestions?  Also,
I would like to propose another DRAW-SURFACE-* type function which takes a
source rectangle (or position) as well as the destination rectangle.
Thoughts?

Thanks,

Anthony
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