[example] tweaking canvas example

1 files changed, 11 insertions, 5 deletions

diff --git a/src/interactive/canvas.lisp b/src/interactive/canvas.lisp
index 2fa341c..ce7829b 100644
--- a/src/interactive/canvas.lisp
+++ b/src/interactive/canvas.lisp
@@ -12,6 +12,9 @@
                             :element-type 'unsigned-byte
                             :initial-element 255))))
 
+(defun pixel-offset (x y pixels)
+  (* 4 (+ x (* y (pixel-width pixels)))))
+
 (let ((cached-pixel))
   (defun pixel (pixels x y &optional (use-cached t))
     "When USE-CACHED is NIL, return a fresh array displaced to
@@ -50,8 +53,7 @@
                          (,a (aref ,pixel-var 3)))
          ,@body))))
 
-(defun pixel-offset (x y pixels)
-  (* 4 (+ x (* y (pixel-width pixels)))))
+
 
 (defmacro with-pixels-rect ((x y r g b a) (pixels &key left right top bottom) &body body)
   "Executes BODY on all pixels in the box bounded by LEFT RIGHT TOP and BOTTOM of PIXELS.
@@ -73,11 +75,15 @@
          (loop for ,x from (if ,lv ,lv 0) below (if ,rv ,rv (pixel-width ,pxs)) do
            (loop for ,y from (if ,bv ,bv 0) below (if ,tv ,tv (pixel-height ,pxs))
                  do (progn
-                      (setf  ,px (adjust-array ,px 4
-                                               :displaced-to (pixels-data ,pxs)
-                                               :displaced-index-offset (pixel-offset ,x ,y ,pxs)))
+                      (setf ,px (adjust-array ,px 4
+                                              :displaced-to (pixels-data ,pxs)
+                                              :displaced-index-offset (pixel-offset ,x ,y ,pxs)))
                       ,@body)))))))
 
+(defun clear-canvas (canvas &key (r 0) (g 0) (b 0) (a 255))
+  (with-pixels-rect (x y pr pg pb pa) (canvas)
+    (setf pr r pg g pb b pa a)))
+
 (defmacro with-pixels-line ((x y r g b a) (pixels start-x start-y end-x end-y) &body body)
   "A convenience macro for doing something to a whole line of pixels -
 e.g., drawing a line in a particular color."