Wednesday, June 14, 2006

Update Functions

Ah, it's been a while.

I managed to get even better performance by precreating all the bitmaps for the cells. Obvious really, but it's now running pretty well.

Since the whole point of this exercise is for me to experiment with lisp features I've been experimenting with storing an update and render closure in each cell. This has worked out really nicely, allowing me to have a more efficient board update when opening up empty cells and also the ability to do neat effects like control the speed that the board opens up.

So the function below creates an update function that'll expose surrounding cells on the next update:

 
(defun show-surrounding-cells ()
(make-updatefn (board ix iy)
(do-surrounding-cells (mine-x mine-y board ix iy)
(let ((cell (aref (board-cells board) mine-x mine-y)))
(when (cell-mine-count cell)
(setf (cell-updatefn cell) (update-expose)))))
nil))


It's also possible to create animation effects by using an update function and a render function sharing the same closure:


(defun hit-mine (cell speed)
(let ((count *cell-size*)
(delay speed))

(labels
((render (bitmap board ix iy left top right bottom cell mouse-inside)

(draw-cell bitmap board ix iy left top right bottom cell mouse-inside)

(let ((remain (- *cell-size* count)))
(alleg:blit *invisible-cell* bitmap
remain remain
(+ remain left) (+ remain top)
(- *cell-size* (* 2 remain)) (- *cell-size* (* 2 remain))))))

(setf (cell-renderfn cell) #'render)

(make-updatefn ()
(cond
((zerop delay) (decf count) (setf delay speed))
(t (decf delay)))
(if (zerop count)
(progn
(setf (cell-renderfn cell) nil)
nil)
self)))))


So this one makes the invisible cell bitmap shrink to nothingness leaving the new one behind.

I can create higher-level update functions as well. One useful one is delay, that just waits a certain number of frames before switching the given function in.


(defun delay-update (count function)
(make-updatefn ()
(decf count)
(if (zerop count)
function
self)))


However, this leaves open the possibility of setting an update function over the top of another one that might be doing useful work. We can deal with this nicely with a combine update function:


(defun combine-updatefn (fn1 fn2)
(make-updatefn (board ix iy)
(setf fn1 (when fn1 (funcall fn1 board ix iy))
fn2 (when fn2 (funcall fn2 board ix iy)))
(cond
((and fn1 fn2) self)
(fn1 fn1)
(fn2 fn2)
(t nil))))


This runs both the update functions, eventually removing itself when one of the sub ones finishes.

As a debugging aid I can print out the current function on each cell, and it should be possible to set it up to inspect a particulary cell by clicking on it. Very cool potential there.

The great thing about this is that means I can store arbitrary data on a cell and do processing on it without having to make room for it in my main cell datastrucure. So by doing this I've decoupled the update logic and animation data from my simple board representation. Of course this sort of thing isn't limited to lisp, but it's an interesting way to think about it that falls into place quite naturally.

My latest distraction is trying to get SLIME and CLISP to work better with macro argument lists. I've been doing some hacking replacing lisp's standard defmacro with my own version that stores away some extra data, but I think the proper solution is going to be modifying CLISP itself.

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