;; I am trying to learn to use cl-opengl by translating some of those ;; examples from the redbook which are not in the distributed code ;; under ../examples/redbook.

;; In particular, I should like to understand some of Ch6 of the Redbook ;; dealing with blending and antialiasing. I began with blending.

;; While I seem to have pieces working, the code below, and its author, ;; are obviously missing one or more essential ideas. I would be happy ;; to learn what they are, so that I can discover how I might had found ;; them out without bothering the list about possibly trivial matters.

;; (lisp-implementation-version) returns ;; Version 1.9-r15972M (linuxX8664) for ccl. ;; I use 2-pane emacs with C-c C-c to move forms from source ;; buffer to *slime-repl ccl* buffer ;; all under Linux Mint 14 (64 bit).

;; Thanks for any and all assistance ;; Cheers /Greg Bennett

;;+ Code and comments on its execution follow.

;; This is blender.lisp ;; An attempt to adapt the code in the ;; OpenGL Programming Guide P230/1 ;; to cl-opengl ;; borrowing from redbook/examples/lines.lisp for basic windowing code, ;; and with helpful hints from Bart Botta about how to convert the C ;; code to opengl's forms.

;; Comparing the Guide with the examples files, I infer that ;; the contents of void inint(void) go to (defmethod (glut:display-window ())) ;; while void display(void) -> (defmethod (glut:display( )))

;; *Typically executing the forms below down to and including ;; (defun (gb-blend( ..)) ;; and then running (gb-blend) produces a solid yellow ;; window. The x in its top right does indeed kill it.

;; Adding the (defmethod keyboard ...) form and running ;; (gb-blend) produces that yellow window, the keys a,s,r,m,x ;; have no effect on it at all.

;; The x in its top right kills it. Esc kills it too and ;; leads to this in the message ;; window of what was the repl: ;+ Lisp connection closed unexpectedly: connection broken ;+ by remote peer

;+ alt-x slime asks whether I want to start another lisp ;+ answer no -> (presumably) the lisp with which contact ;+ had been severed. This repl knows about nothing which ;+ preceded its interruption.

;; I said Typically, because just ONCE the code without ;; the keyboard method produced a yellow pane with a white ;; square in its centre.

;; Adding the keyboard method to this -> that same pair ;; which reacted to the keys as described on P230 in respect ;; of the white square: ;; a no change ;; s white -> blue ;; r blue -> yellow ;; m yellow -> black ;; x black -> white ;; Esc graceful fold.

;; Having closed the window, ;; immediately re-doing (gb-blend) -> that same collection ;; of responses to keys.

;; Closing lisp, redoing the whole exercise from ;; the same, unchanged, source file -> only the ;; solid yellow pane, unchanged by key presses, save Esc which ;; produces the train wreck described earlier.

;; A package (defpackage :zot (:use :cl))

;; Use it (in-package :zot)

;; Class for windows in which blending actions should occur (defclass blender-window (glut:window) () (:default-initargs :width 400 :height 400 :pos-x 50 :pos-y 50 :mode '(:single :rgb) :title "Blender Window"))

;; Set up some attributes ;; Described as in void init(void) on P230 (defmethod glut:display-window ((w blender-window)) (gl:clear-color 1.0 1.0 0.0 0.0) (gl:blend-func :one :one) (gl:enable :blend) )

;; We seem to need this reshape method ;; in order that anything show on the screen (defmethod glut:reshape ((w blender-window) width height) (gl:viewport 0 0 width height) (gl:matrix-mode :projection) (gl:load-identity) (glu:ortho-2d 0 width 0 height))

;; A method on display to get what seems ;; to be a rectangle to be modified by blending actions ;; code in void display(void) on P230 (defmethod glut:display ((w blender-window)) (gl:clear :color-buffer-bit) (gl:color 0.0 0.0 1.0) (gl:rect -0.5 -0.5 0.5 0.5) (gl:flush))

(defun gb-blend () (glut:display-window (make-instance 'blender-window)))

;; If I have translated correctly, that's all I need. ;; Let's make a blender-window

;; There is it in the top left of the screen ;; correct title, solid yellow background. ;; (? Should there have been a yellow square in the middle ?) ;; On to blending through the keyboard.

;; The keyboard method to drive the blender options ;; in the OpenGL P G P231 (defmethod glut:keyboard ((w blender-window) key x y) (declare (ignore x y)) (case key ((#\a) (gl:blend-equation :func-add)) ((#\s) (gl:blend-equation :func-subtract)) ((#\r) (gl:blend-equation :func-reverse-subtract)) ((#\m) (gl:blend-equation :min)) ((#\x) (gl:blend-equation :max)) ((#\Esc) (glut:destroy-current-window)) ) (glut:post-redisplay) )

;; Assuming correct translation, run (gb-blend) and press 'a' ;; The story is at the top of the file.