baking shadow to light map for direct sun light

[shuipi]

I know this is a very old technology but it's the first time I implement it. So my question is, since the sun light is directional light, when baking its shadow, I just shoot rays in the negative sun light direction and see if it hits anything, but this can only give a sharp edged shadow, and together with the low resolution light map, the result looks very bad. However in all the games that do this, the baked shadow looks very soft. I can think of several methods that could soften the shadow, but I want to ask what's the best way (or the most used way) to do it?

 

[jlippo]

Try shooting several rays into a disk with size of '0.5 degrees and you have decently accurate result for our sun, just average the results for each pixel.
For anti aliasing jitter the location from where you shoot the sample along the surface as well. (preferably within the sample.)