Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/09/16/drawing-complex-rectangles-in-flex-using-the-graphicsutil-class/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        creationComplete="init()">

    <mx:Script>
        <![CDATA[
            import mx.styles.StyleManager;
            import mx.utils.GraphicsUtil;

            private var fillColor:uint;

            private function init():void {
                fillColor = StyleManager.getColorName("haloOrange");

                box.graphics.clear();
                box.graphics.beginFill(fillColor);
                GraphicsUtil.drawRoundRectComplex(box.graphics,
                                                    0,
                                                    0,
                                                    box.width,
                                                    box.height,
                                                    topLeft.value,
                                                    topRight.value,
                                                    bottomLeft.value,
                                                    bottomRight.value);
            }
        ]]>
    </mx:Script>

    <mx:ApplicationControlBar dock="true">
        <mx:Form>
            <mx:FormItem label="topLeft:">
                <mx:HSlider id="topLeft"
                        minimum="0"
                        maximum="{box.height / 2}"
                        snapInterval="1"
                        tickInterval="10"
                        liveDragging="true"
                        change="init();" />
            </mx:FormItem>
            <mx:FormItem label="topRight:">
                <mx:HSlider id="topRight"
                        minimum="0"
                        maximum="{box.height / 2}"
                        snapInterval="1"
                        tickInterval="10"
                        liveDragging="true"
                        change="init();" />
            </mx:FormItem>
            <mx:FormItem label="bottomLeft:">
                <mx:HSlider id="bottomLeft"
                        minimum="0"
                        maximum="{box.height / 2}"
                        snapInterval="1"
                        tickInterval="10"
                        liveDragging="true"
                        change="init();" />
            </mx:FormItem>
            <mx:FormItem label="bottomRight:">
                <mx:HSlider id="bottomRight"
                        minimum="0"
                        maximum="{box.height / 2}"
                        snapInterval="1"
                        tickInterval="10"
                        liveDragging="true"
                        change="init();" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:Box id="box" width="240" height="160" />

</mx:Application>

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