Tuesday, December 30, 2008

Visibility System And Shadow Casters

hi, last days i'v been working on my visibility system, rendering system and redesign few things related to them, also fix some low performance issues in big levels.
so in order to attack those issues i stared so see what could be optimized, one thing was the pvs data set which was basically a list of visible objects created from specific view point.
this pvs is needed for both camera and lights, also mirror materials needs to generate this set for the mirror generation pass.
those list was filled in few places but the thing is that we could do alot of the work in load time and achive better performance and still get the same thing.
so instead of keeping list of scene objects which could be changed doring the game (for example: another bot got in or out), i'm using a bit set for lights and camera pvs.
each entity update which areas they belong to, lights only update thier bit set when they move/change.
when i want to render the scene, i only need to check camera pvs bit set and see which areas are visible. to know which entity is visible is just a matter of checking the right bits in camera bit set.
in lighting pass we need to know which areas the current light influenced, so to get this info we need to do an AND bit operator between current light bit set and camera bit set, the result is the areas the light can influence and the camera can see.
the same thing is done for shadows generation, that using the same light bit set pvs with an exception.
when we are generating shadows we still need to consider shadows that comes from unvisible objects, object that is not visible still can cast visible shadow!
to solve this issue, we should check if the shadow volume of that object is intersecting our view frustum, if so it means this object needs to be rendered into the shadow map even if its not visible!.
if you dont handle those object you will get wrong shadows.
for example: if you have an open space scene with sun as the only light source and simple cave built from floor, ceiling and walls. when you enter the cave and look down (ceiling is not visible!) you still want to see the shadow of the ceiling.
here is screenshots from medium scene with unvisible shadow caster

shadows off

shadows generating from unvisible ceiling of this hallway

2 comments:

guardian said...

really slick!

do you plan to release this engine? or at list executable demos?

i skimmed through the list of posts, all look really nice

keep up the good work :)

orenk2k said...

hi
well, my main thing is to make the engine fast enough so the game could be played smoothly in medium/big levels.
this is not an easy task and always takes more than i thought it will - i'm still working on it on my free time :)
demo? not really a demo, more like a pre pre alpha :)
i dont want to say the right date for it because what i wrote before, but i want to release something so i could know what you think i should do better and besides hear what you think about it in general.
thanks