oneliner-paint-drops.r

Author: Vincent Ecuyer
Date: 29-Jan-2013

Contents:

1. Purpose

Simple demo showing color drops fading in the background as more are added.

2. Note

Not compatible with current REBOL releases - REBOL/View 1.2.x is needed. This oneliner used a trick with the draw block in the face effect: when a time delay or a frequency is specified in older versions of /View, the draw block is evaluated at each tick, and words coming from the parent context are allowed. Nearly any code can be used inside a paren! ( ), as long as the value of the last element is legit in the draw block.

This doesn't work anymore because the draw dialect only does words lookup, but not a full evalution, which is a good thing security-wise.

3. Usage

Just launch the script, or copy/paste the line in the /View console.

4. Commented Code

; builds and shows a window
view layout [

    ; a 100x100 box updated 9 times a second
    b: box rate 9 effect [
        ; the effect is based on the interaction between the effect 
        ; block and the image attribute

        ; paints a small circle filled with a random color 
        ; (0.0.0 to 240.240.240) in a random place in the box
        draw [pen (random snow) circle (random 99x99) 2]

        ; mixes the new drop with the already blurred ones in b/image
        blur
    ]

    ; a very small box (just visible enough to receive event) 
    ; updated 9 times a second
    box 1x1 rate 9 effect [
        ; makes a copy of the other box as it's displayed 
        ; before it changes its content 
        ; and places this copy in the background
        draw [(b/image: to-image b)]
    ]
]

5. Updated Version

Not as short (154 chars at best when removing spaces and comments), but this does work in REBOL/View 2.7.8:

; draw block: 
; in any color between 0.0.0 and 240.240.240, 
; draws a filled circle anywhere inside the 100x100 default box
d: [pen (random snow) circle (random 99x99) 2]

; builds and shows a window
view layout [
    ; a box with an effect: the draw block and the blur for fading
    b: box rate 9 effect [draw [] blur] feel [
        engage: does [
            ; paints a new drop (changes the draw block)
            b/effect/2: compose d
            ; saves the blurred result as a background
            b/image: to-image b
            ; updates the box
            show b
        ]
    ]
]