View this example as SVG (Adobe viewer or Firefox)

This is one of my favourite examples. It uses a radial fill on the background to give the effect of back-lighting, and both the title text and the distant surface are semi-transparent to emphasise the effect.

Transparency

This can be achieved directly in the heading, simply by defining a font such as:

ch.DefineFont'AX' 'Arial,opacity:0.7'

As you can see, this syntax can be used to pass any SVG style attributes directly into the finished page. The gradients are defined in the APL code by the lines:

 ch.DefineTile 17 '#radial1'
 ch.DefineTile 23 '#fill1'
 ch.DefineTile 24 'fill:url(#fill2); opacity:0.25' 

If you simply provide a URL, RainPro assumes you mean a gradient fill and wraps it for you in the correct tag. If you want a combination (in this case a gradient and transparency are combined) you have to give both attributes in full. Incidentally SVG is case-sensitive here, so be careful to use lower-case for the attribute names.

Defining the radial fill

This has a few more options to tweak, but the principle is much the same as the linear fills:

This time, is is convenient to use the filled rectangle itself as the co-ordinate system for the radial fill. The bright spot is 25% of the way down (and right) from the top left corner and the fill will scale to fit the shape of the rectangle. This one just runs from a white centre to a Navy background. Note that you can have as many colours in here as you like, for example:

View this example as SVG

... which is a visual nightmare, but does illustrate the possibilities rather well:

Summary

Used carefully, transparency is a very effective tool when drawing charts with large slabs of colour. It is also a nice trick to play with the title text when this is used on top of a radial-fill backdrop.