In the renderers, dlightbits are never cleared from world surfaces.
The dlight image does not repeat, so if it draws on extra surfaces it's
not visible.
However if using a repeating image (tr.defaultImage instead of tr.dlightImage);
* In OpenGL1 image is only drawn on surfaces close to dlight origin.
* In OpenGL2 image is draw on surfaces clearly outside the dlight radius, including past non-dlighted surfaces.
It seems there was a similar issue with pshadowBits. So update surface
dlightBits even if 0, like already done for pshadowBits. This causes
only surfaces close to origin to be affected. (Though it is a little
farther than in OpenGL1.)
I have no idea why this isn't a problem in OpenGL1.
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