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Re: 2D graphics/turtle lib suitable for kids?
Posted: Fri Jan 07, 2011 5:48 am
by yena
I wrote a simple turtle graphics library based on lispbuilder-sdl. The code can be found here:
https://github.com/johanberntsson/cl-tu ... urtle.lisp
Re: 2D graphics/turtle lib suitable for kids?
Posted: Sun Jan 09, 2011 2:17 pm
by Warren Wilkinson
You're not teaching trigonometry, but basic geometry. You're still working from coordinates, just abstract ones. fd 1 (forward one, in a hypothetical dialect) could be one pixel (it was in Apple Logo) but it could also be an arbitrary distance, with 1.235 as a possibility, as well.
Advocating direct pixel manipulation seems... archaic, and non-portable to higher/lower resolutions.
SVG is much more flexible than (insert bitmapped format).
NeWS was much more flexible than X.
Artists don't draw on graphing paper, yo.
I like this topic =). Grid drawing is called pixel art:
http://www.pixeljoint.com/pixels/new_ic ... ?ob=rating, I did it all the time to make sprites. Flexibility of the output isn't important here, simplicity of ideas is (she'll ask "How can I make it red?" long before she'll ask "How can I make it 1024x768 triple buffered with 32 bits, an alpha channel and a Z buffer?" -- hyperbole I know)
Direct pixel manipulation is the simplist, most primitive and most portable way of doing graphics. All other interfaces are just predefined pixel plotting routines. Algebra is the arithmatic as vectors are to pixels. My suggestion is to start at the logical beginning (pixels) and grow upwards to turtles (or gradients, or boxes, or triangles, or sprites, or text or whatever your kid is interested in).
What good is turtles when you want gradients? I'd bet she'd prefer making gradient rainbows to manipulating a turtle. Pixel plotting can, with equal ease, do both.
Re: 2D graphics/turtle lib suitable for kids?
Posted: Sun Jan 09, 2011 7:56 pm
by Warren Wilkinson
I wanted to demonstrate the simplicity of raw pixel pushing. I wrote the library I was talking about, it took under an hour. It requires SDL, SBCL, and no other libraries.
Makefile
Code: Select all
gfx.so : gfx.c
gcc -c -fPIC `sdl-config --cflags` `sdl-config --libs` gfx.c && ld -shared -o gfx.so gfx.o
Code: Select all
#include "SDL/SDL.h"
SDL_Surface* screen = NULL;
int sdl_start (int x, int y, int d) {
if (SDL_Init( SDL_INIT_VIDEO | SDL_INIT_EVENTTHREAD ) != 0) { return -1; }
screen = SDL_SetVideoMode( x, y, d, SDL_SWSURFACE );
if (screen == NULL) { return -1; }
return 0;
}
void sdl_stop () {
SDL_FreeSurface( screen );
screen = NULL;
SDL_Quit();
}
char* gfx_error () { return SDL_GetError(); }
void gfx_show () { SDL_Flip(screen); }
void* gfx_raw () { return screen->pixels; }
void gfx_lock () { SDL_LockSurface(screen); }
void gfx_unlock () { SDL_UnlockSurface(screen); }
Code: Select all
(defpackage :gfx
(:use :common-lisp :sb-alien)
(:export ;; +width+ +height+ +depth+
+wide+ +tall+ +white+ +black+ +red+ +green+ +blue+
gfx-start gfx-stop gfx-show put))
(in-package :gfx)
(load-shared-object "libSDL.so")
(load-shared-object (car (directory "gfx.so"))) ;; Get the abs path of gfx.so.
(define-alien-variable screen system-area-pointer)
(define-alien-routine sdl-start int (width int) (height int) (depth int))
(define-alien-routine sdl-stop void)
(define-alien-routine gfx-error c-string)
(define-alien-routine gfx-show void)
(define-alien-routine gfx-raw system-area-pointer)
(define-alien-routine gfx-unlock void)
(define-alien-routine gfx-lock void)
(defconstant +width+ 800)
(defconstant +height+ 600)
(defconstant +depth+ 32)
(defconstant +white+ #xFFFFFF)
(defconstant +black+ #x000000)
(defconstant +red+ #xFF0000)
(defconstant +green+ #x00FF00)
(defconstant +blue+ #x0000FF)
(defun gfx-start ()
(if (zerop (sb-sys:sap-int screen))
(or (zerop (sdl-start +width+ +height+ +depth+))
(error (gfx-error)))
(error "Graphics are already initialized")))
(defun gfx-stop ()
(if (zerop (sb-sys:sap-int screen))
(error "Graphics are not initialized.")
(sdl-stop)))
(defun dot (color x y)
(setf x (min (max x 0) +width+) y (min (max y 0) +height+))
(let ((offset (ash (+ (* y +width+) x) 2)))
(setf (sb-sys:sap-ref-32 (gfx-raw) offset) color)))
(defconstant +wide+ (/ +width+ 8))
(defconstant +tall+ (/ +height+ 8))
(defun put (color x y)
"Puts an 8x8 pixels on the screen."
(setf x (* x 8) y (* y 8) color (truncate color))
(gfx-lock)
(dotimes (dx 8) (dotimes (dy 8) (dot color (+ x dx) (+ y dy))))
(gfx-unlock)
(gfx-show))
(gfx-start)
(push #'gfx-stop sb-ext:*exit-hooks*)
The basic idea is to keep the code simple enough so that the library is a part of the learners world -- nothing up our sleeves. Simple libraries can be changed, and in my book that beats configurability.
Sat Jan 22 --
I've written a blog post on this.
Re: 2D graphics/turtle lib suitable for kids?
Posted: Sun Jan 09, 2011 8:36 pm
by TheGZeus
Warren Wilkinson wrote:You're not teaching trigonometry, but basic geometry. You're still working from coordinates, just abstract ones. fd 1 (forward one, in a hypothetical dialect) could be one pixel (it was in Apple Logo) but it could also be an arbitrary distance, with 1.235 as a possibility, as well.
Advocating direct pixel manipulation seems... archaic, and non-portable to higher/lower resolutions.
SVG is much more flexible than (insert bitmapped format).
NeWS was much more flexible than X.
Artists don't draw on graphing paper, yo.
I like this topic =). Grid drawing is called pixel art:
http://www.pixeljoint.com/pixels/new_ic ... ?ob=rating, I did it all the time to make sprites. Flexibility of the output isn't important here, simplicity of ideas is (she'll ask "How can I make it red?" long before she'll ask "How can I make it 1024x768 triple buffered with 32 bits, an alpha channel and a Z buffer?" -- hyperbole I know)
Direct pixel manipulation is the simplist, most primitive and most portable way of doing graphics. All other interfaces are just predefined pixel plotting routines. Algebra is the arithmatic as vectors are to pixels. My suggestion is to start at the logical beginning (pixels) and grow upwards to turtles (or gradients, or boxes, or triangles, or sprites, or text or whatever your kid is interested in).
What good is turtles when you want gradients? I'd bet she'd prefer making gradient rainbows to manipulating a turtle. Pixel plotting can, with equal ease, do both.
I'm recommending a more high-level programming technique.
I find it interesting that one would recommend low-level, direct bit manipulation in a language like Lisp, which is so high-level, and abstracts away things like memory management.
Then again, I'm the guy who's hoping to re-implement a NeWS-alike with native PostScript 3D graphics in the next few years.
While bitmaps will be available, and bitmapping of objects will obviously be a priority, resolution-independence across the board is of higher importance.
Re: 2D graphics/turtle lib suitable for kids?
Posted: Sun Jan 09, 2011 11:56 pm
by Warren Wilkinson
I'm all for simplicity, and I'll take it in whatever form it comes in, low level or high.
Resolution independence shouldn't be that hard: turn +width+ and +height+ to *width* and *height*, set them to your resolution and rerun the program. That is how postscript does it, it's just a variant of Forth.
A high level approach might incorrectly teach her that computers are the abstractions they implement. Instead, teach the real comp-sci stuff, because in this case its just as easy (or easier) than turtle graphics (which is a dead-end API) -- why not go with the facts?
Re: 2D graphics/turtle lib suitable for kids?
Posted: Mon Jan 10, 2011 8:33 am
by TheGZeus
Warren Wilkinson wrote:I'm all for simplicity, and I'll take it in whatever form it comes in, low level or high.
Resolution independence shouldn't be that hard: turn +width+ and +height+ to *width* and *height*, set them to your resolution and rerun the program. That is how postscript does it, it's just a variant of Forth.
A high level approach might incorrectly teach her that computers are the abstractions they implement. Instead, teach the real comp-sci stuff, because in this case its just as easy (or easier) than turtle graphics (which is a dead-end API) -- why not go with the facts?
Ah, I see.
When you mentioned BASIC in a positive light, I misunderstood your intentions.
I think having both direct pixel manipulation and higher-level geometric stuff available is a good idea. Options.
Heck, PS can display bitmap images, too.
Re: 2D graphics/turtle lib suitable for kids?
Posted: Wed Jan 12, 2011 4:59 am
by paulitiger
Hello.
I know: this is the Common Lisp section -- but:
I tried a turtle interface via
Clojure. And it worked very well, without large programming work.
Here is a small code example:
(import '(ch.aplu.turtle Turtle))
(def t1 (new Turtle))
(defn mt []
(dotimes [_ 50]
(.left t1 110)
(.forward t1 100)))
This produces a small star in the turtle window.
You can get the necessary Java Lib from:
http://www.aplu.ch/home/apluhomex.jsp
Kind Greetings
Re: 2D graphics/turtle lib suitable for kids?
Posted: Tue Jan 18, 2011 2:08 pm
by Jasper
cl-cairo2(
github) would be good for it especially if we also could easily have keyboard/mouse/etc input in conjunction with it, and it has much more drawing ability. Neat to be able to export to many things, svg, ps, pdf, png, X11 window. Maybe i'll see if i can add a function to give sdl an cairo surface. Note: if it becomes slow, you need to may need to lock it. cl-cairo2:sync-lock, and use sync-reset and then locking again to draw. (I don't understand why that continuously costs cpu if unlocked, afaiks no way to change what is already drawn looking at the
api.)