I would like to know, how dynamic shadows, that 'blend' onto other objects, are created.
2 Answers
These can be done using shadow mapping. Basically, place the camera at the light source and render the scene into a depth buffer; the resulting buffer identifies all the lit surfaces since they are just the surfaces the light can "see". This texture is then used in the pixel shaders in the main render to mask away light on surfaces behind the shadow map. There are plenty of shadow mapping tutorials on the Web, so consult those for details.
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1\$\begingroup\$ On the screen shot there is one Omnidirectionnal shadowmap light, you might want to check out dual paraboloid shadowmaps or shadowmaps with cubemaps for those. \$\endgroup\$– ValmondCommented Feb 4, 2012 at 7:34
Assuming you know how to generate a shadow for an object, generate all the shadows separately, and then blit them onto the scene. Any overlaps will have the sum of their... darkness (as it were), and therefore look like the shadows overlap.