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Flash 8 帮助文件curveTo方法中画圆函数的语义错误

👤 dnawo 📅 2007-06-18 👁 7729 👍 0 💬 0 🔄 来源:本站原创
在Flash8帮助文件讲述curveTo方法时举了个创建圆形的例子,如下:

this.createEmptyMovieClip("circle2_mc", 2);
circle2_mc.lineStyle(0, 0x000000);
drawCircle(circle2_mc, 100, 100, 100);
function drawCircle(mc:MovieClip, x:Number, y:Number, r:Number):Void {
mc.moveTo(x+r, y);
mc.curveTo(r+x, Math.tan(Math.PI/8)*r+y, Math.sin(Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y);
mc.curveTo(Math.tan(Math.PI/8)*r+x, r+y, x, r+y);
mc.curveTo(-Math.tan(Math.PI/8)*r+x, r+y, -Math.sin(Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y);
mc.curveTo(-r+x, Math.tan(Math.PI/8)*r+y, -r+x, y);
mc.curveTo(-r+x, -Math.tan(Math.PI/8)*r+y, -Math.sin(Math.PI/4)*r+x, -Math.sin(Math.PI/4)*r+y);
mc.curveTo(-Math.tan(Math.PI/8)*r+x, -r+y, x, -r+y);
mc.curveTo(Math.tan(Math.PI/8)*r+x, -r+y, Math.sin(Math.PI/4)*r+x, -Math.sin(Math.PI/4)*r+y);
mc.curveTo(r+x, -Math.tan(Math.PI/8)*r+y, r+x, y);
}


前三个坐标位置如下图所示:

图片

对于例子函数中的( Math.sin(Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y)坐标,实际应是( Math.cos(Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y),由于Math.sin(Math.PI/4)和Math.cos(Math.PI/4)在值上是相等的,因而结果并没显示错误,但在语义上是错的,正确的应是:

this.createEmptyMovieClip("circle2_mc", 2);
circle2_mc.lineStyle(0, 0x000000);
drawCircle(circle2_mc, 100, 100, 100);
function drawCircle(mc:MovieClip, x:Number, y:Number, r:Number):Void {
    mc.moveTo(x+r, y);
    mc.curveTo(r+x, Math.tan(Math.PI/8)*r+y, Math.[color=Red]cos[/color](Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y);
    mc.curveTo(Math.tan(Math.PI/8)*r+x, r+y, x, r+y);
    mc.curveTo(-Math.tan(Math.PI/8)*r+x, r+y, -Math.[color=Red]cos[/color](Math.PI/4)*r+x, Math.sin(Math.PI/4)*r+y);
    mc.curveTo(-r+x, Math.tan(Math.PI/8)*r+y, -r+x, y);
    mc.curveTo(-r+x, -Math.tan(Math.PI/8)*r+y, -Math.[color=Red]cos[/color](Math.PI/4)*r+x, -Math.sin(Math.PI/4)*r+y);
    mc.curveTo(-Math.tan(Math.PI/8)*r+x, -r+y, x, -r+y);
    mc.curveTo(Math.tan(Math.PI/8)*r+x, -r+y, Math.[color=Red]cos[/color](Math.PI/4)*r+x, -Math.sin(Math.PI/4)*r+y);
    mc.curveTo(r+x, -Math.tan(Math.PI/8)*r+y, r+x, y);
}

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