Rebol/Red 中的彩色绘图

Question

在来自 http://business-programming.com/business_programming.html 的以下代码中，我想添加一个按钮来转换以蓝色而不是白色绘制的线条。我尝试在不同的地方添加 color: blue 但它不起作用：

view center-face layout [
      ; color: blue                                     ; does not work.
    s: area black 650x350 feel [
        engage: func [f a e] [
              ; color: blue                             ; does not work here also.
            if a = 'over [
                append s/effect/draw e/offset
                show s
            ]
            if a = 'up [append s/effect/draw 'line] ; tried adding "'pen 'blue" here before 'line
        ]
    ] effect [draw [line]]
    b: btn "Save" [
        save/png %a.png to-image s 
        alert "Saved 'a.png'"
    ]
    btn "Clear" [
        s/effect/draw: copy [line]
        show s]
    ]

如何让线条以蓝色而不是白色绘制？

Answer 1

修改

] effect [draw [line]]

至

] effect [draw [pen blue line]]

见REBOL 2: View Draw Dialect

Rebol/Red 中的彩色绘图

Drawing in color in Rebol/Red

draw

rebol