Stencil shadow deformation based on lighting direction

[Jay Dolan]

I posted this on SO, but this might actually be the best crowd to run this by. I've calculated an average light direction for my mesh entities, and I'd like to deform their stencil shadows away from the light source. Here's the issue I posted on StackOverflow:

http://stackoverflow.com/questions/2018 ... ght-source

Any insight you guys can share would be much appreciated!

[Spike]

I assume you're after projected shadows and not shadow volumes?

something like http://www.opengl.org/archives/resource ... sld021.htm ? you'll still need to combine that with a model and projection matrix, probably by multiplying that matrix into the (model)view matrix at some point.

z-pass shadow volumes need just the sides, which requires that only some verts are extruded based upon the light position. z-fail needs front+back as well, but if you're already generating sides then its simpler to keep the front+back caps as part of the same mesh/batch. aside from you calling it 'stencil shadows', your matrix stuff seems unrelated...

[Irritant]

Jay, CRX used to have exactly the code you're looking for, where the stencil shadows were stretched/deformed based on light direction, for a very fast, simple method of shadowing. I think that code was in the engine in SVN around 2006-2010, it was pretty efficient and fast, which is what I assume you're going for. Only issue was of course that it didn't project on walls, or get clipped on the edges of brushes, etc, but that was the tradeoff for speed vs true shadow volumes.

[Knightmare]

[jitspoe]

What many engines refer to as "stencil shadows" are the planar shadows, but rendered to the stencil buffer to avoid the ugly zfighting the original shadows had.

[Knightmare]

[Barnes]

[Knightmare]

It originally came from Quake2Max, right?

BTW, KMQ2 does all 3 variants: static planar, dynamic planar, and volume projection shadows.

[Barnes]

[leileilol]

I think even Quake3 does this with cg_shadows 2.

[Barnes]

cg_shadows 1 - planar blob shadow
cg_shadows 2 - projective shadow volumes (zpass) shadows hit through the walls
cg_shadows 3 - opacity projective planar shadow

[Jay Dolan]

[Barnes]

Very nice, but i'm don't understand one thing - it's not shadow volumes, right?

[Jay Dolan]

[Spike]

gl3+ method (according to docs. seems to fail on nvidia):
glGetFramebufferAttachmentParameteriv(GL_FRAMEBUFFER, GL_STENCIL, GL_FRAMEBUFFER_ATTACHMENT_STENCIL_SIZE, &someinteger);
deprecated method (which fails on a core context):
glGetIntegerv(GL_STENCIL_BITS, &someinteger);

with d3d10+, microsoft document:
DXGI_FORMAT_D32_FLOAT_S8X24_UINT
DXGI_FORMAT_D32_FLOAT
DXGI_FORMAT_D24_UNORM_S8_UINT
DXGI_FORMAT_D16_UNORM
which means they don't consider that hardware could support any sorts of depthstencil configuration with stencil bits other than 0 or 8bit.
of course, there's nothing stopping you from asking for more than 8 bits from gl. you probably won't get it though.