I've been reading Filthy Rich Clients for quite a while and got some inspiration with chapter 7: Gradients. Somewhere along the chapter Romain shows the power of RadialGradientPaint by creating the illusion of a sphere with 3 gradients applied on a circular shape, something like the following picture



The process for drawing such a sphere as described in the book, requires 3 different paints applied one at a time over the same shape; the way paints currently work on GraphicsBuilder is pretty straight forward: set paint, fill shape, you are done. So how can 3 paints be applied over the same shape? the answer is multiPaint. MultiPaint is a group of paint operations, like gradientPaint, radialGradient and the other paints describe here. The code used to produce the previous image follows
def width = 200 def height = 200 renderingHint( key: 'antialiasing', value: 'antialias on' ) circle( cx: width/2, cy: height/2, radius: width/2, borderColor: false ){ multiPaint { radialGradient( cx: width/2, cy: height/2, radius: width/2 ) { stop( offset: 0, color: color(red: 6, green: 76, blue: 160, alpha: 127) ) stop( offset: 1, color: color(alpha: 204) ) } def lighting = color(red: 64, green: 142, blue: 203, alpha: 255) radialGradient( cx: width/2, cy: height*1.5, fx: width/2, fy: (height*1.75)+6, radius: width/2 ) { stop( offset: 0, color: lighting ) stop( offset: 0.8, color: lighting.derive(alpha:0) ) transformations{ scale(y:0.5) } } radialGradient( cx: width/2, cy: height/2, fx: 45, fy: 25, radius: width/1.4 ){ stop( offset: 0, color: color('white').derive(alpha:0.4) ) stop( offset: 0.5, color: color('white').derive(alpha:0) ) } } }
Notice that there is a color operation which serves a java.awt.Color factory depending on the properties you pass to it (default value for each unspecified color property is 0, 1 for alpha). Color has also been groovified with a derive method that creates a copy of the target color and changes the specified color components. Lastly, radialGradient now accepts transformations too, there are still some issues to be solved in terms of relative positions though (absolute=true).

Keep on Groovying!