This tool does not support gradient fills. However, a smooth bevel filter can be used to produce a linear gradient fill. More complex fills can also be created in external graphic applications as images, and then used with masks to fill other graphics.
Example
<slickboard>
<!-- a blue rectanglw with a smooth bevel that acts as a gradient fill -->
<rect x='140' y='50' width='200' height='200' fill_color='8888ff' bevel='gradient' />
<filter>
<bevel id='gradient' distance='100' angle='120' blurX='128' blurY='128' highlightColor='ff0000'
highlightAlpha='.5' shadowColor='0000ff' shadowAlpha='.5' strength='1' quality='3' />
</filter>
</slickboard>
<slickboard>
<!-- masked object -->
<object>
<!-- image created in Photoshop to use as a fill for the star object -->
<image url='images/fill.jpg' x='145' y='50' width='190' height='185' />
<mask target='star' />
</object>
<!-- masking object -->
<object id='star' offset_x='145' offset_y='50'>
<!-- a star -->
<polygon>
<point x='96' y='0' />
<point x='118' y='69' />
<point x='191' y='69' />
<point x='132' y='111' />
<point x='154' y='180' />
<point x='96' y='138' />
<point x='37' y='180' />
<point x='59' y='111' />
<point x='0' y='69' />
<point x='73' y='69' />
<point x='96' y='0' />
</polygon>
</object>
</slickboard>