diff options
| -rw-r--r-- | examples/10-canvas-sneks.lisp | 25 |
1 files changed, 20 insertions, 5 deletions
diff --git a/examples/10-canvas-sneks.lisp b/examples/10-canvas-sneks.lisp index 453ef0e..a69b429 100644 --- a/examples/10-canvas-sneks.lisp +++ b/examples/10-canvas-sneks.lisp @@ -37,6 +37,11 @@ (setf (dy snek) (random-between -1 1)))) (defun advance-snek-pos (snek) + "Advance a snek's position. Check that the snek remains contained in +its HOME. If it isn't, revert position and have the snek change its +mind about where it wants to go. Finally, update the snek's BOD, +ensuring that its BOD is no longer than LEN, truncating it when +necessary." (with-slots (x y dx dy home bod len) snek (incf x dx) (incf y dy) @@ -46,10 +51,12 @@ (snek-change-mind snek)) (push y bod) (push x bod) - (when (< len (length bod)) + (when (<= (* 2 len) (length bod)) (setf bod (nreverse (cddr (nreverse bod))))))) (defun snek-thots (snek) + "A SNEK will decide to change direction the longer it has been +moving in a particular direction." (incf (brain snek) 0.01) (when (< (random 1.0) (brain snek)) (setf (brain snek) 0.0) @@ -59,15 +66,20 @@ (advance-snek-pos snek) (snek-thots snek)) +(defvar *alpha-step* 10) + (defun draw-snek (snek canvas) + "Draws a snek to a canvas. The BOD of a snek is a list of recent +positions that the snek's head had occupied. The body is drawn by +reducing the alpha of the snek's COLOR by 10 for every point in the BOD." (with-slots (bod color) snek (destructuring-bind (red green blue) color - (let ((alpha 255)) + (let ((alpha (max 0 (- 255 (* *alpha-step* (/ (length bod) 2)))))) (loop - for (x y . more) on bod by #'cddr + for (y x . more) on (reverse bod) by #'cddr do (ww::with-pixel (r g b a) (ww::pixel canvas x y) (setf r red g green b blue a alpha)) - (setf alpha (max 0 (- alpha 10)))))))) + (setf alpha (min 255 (+ alpha *alpha-step*)))))))) (defun random-snek (&optional (boundx 100) (boundy 100)) (make-instance 'snek @@ -81,6 +93,8 @@ (ww:defhandler sneks-a-go-go (ww::on-perframe (app ticks) + "Clears cavnas. Moves gives each snek its turn. Draws each + snek. Updates the screen." (with-slots (sneks snek-pit) app (ww::clear-canvas snek-pit) (dolist (snek sneks) @@ -89,7 +103,8 @@ (ww::blit snek-pit)))) (defmethod ww::boot ((app sneking )) - "Adds the intro text and sets up the start button handler." + "Sets up snek-pit, a canvas to which sneks are drawn. Creates random +sneks. Adds the canvas to the app, and sets up the perframe handler." (setf (snek-pit app) (make-instance 'ww:canvas :pixel-width 100 :pixel-height 100) (sneks app) |