Re: [Algorithms] Deferred shadow mask generation

[Francis B. <fra...@ub...>]

Are you also blurring the Shadow collector texture afterwards to get =
smoother looking shadows?  If so, how do you avoid the typical "halo" =
effect when using such a technique?

________________________________

From: gda...@li... =
[mailto:gda...@li...] On Behalf Of =
Wolfgang Engel
Sent: Thursday, April 05, 2007 11:42 AM
To: 'Game Development Algorithms'
Subject: Re: [Algorithms] Deferred shadow mask generation



<<<=20

Now render all gathered Shadowmap in a preprocess (Deferred Shadowing) =
-> Shadow collector

   Render each Shadowmap collected from the viewer point of view and =
store the shadow factor in a screen-sized texture

   Render Cascaded Shadowmap (Put the 4 light space matrix in constant =
register and select the right light projection to use via compare/dot =
product)

   And store the shadow factor...

<<<=20

You can render the four maps into the shadow collector in one pass.

You just fetch the shadow collector then as a screen-space texture for =
each object ... e.g. you use the vpos register in the pixel shader or =
calculate the screen space position in the vertex shader.

=20

So overall five render passes: four to create the shadow maps, one into =
the shadow collector and the one in the shadow collector is also the Z =
pre-pass.

=20

<<<=20

When you said to store shadow factor in r, g or b channel, you mean that =
the different shadow factor must not be blend together and should be =
left separated

Until they are use for lighting calculation ? So in the above =
description, spot light should be render in r channel and cascaded in g, =
then at lighting do two texture fetch ?

<<<=20

You might want to use different colors for different shadows. Cloud =
shadows should be more faint and the shadows casted by objects on the =
ground stronger.=20

=20

Z pre-pass: you have to render like this anyway, why not just use the =
shadow collector pass for this :-)

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- Wolfgang

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=20

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From: gda...@li... =
[mailto:gda...@li...] On Behalf Of =
Lagarde S=E9bastien
Sent: Thursday, April 05, 2007 1:26 AM
To: 'Game Development Algorithms'
Subject: Re: [Algorithms] Deferred shadow mask generation

=20

Alright, I have checked your article and the paper mentioned (PSSM), =
thanks for the pointer.

=20

So If I have well understood:

=20

In a first time you render all the shadowmap for your game:

Render Shadowmap for projected ligt

Render Shadowmap for omni light with cubemap or multiple frustum

Etc...

Render Cascaded Shadowmap for the sun light (with day and light cycle =
managed):

    Here for the directional light representing the Sun

    you render 4 Shadowmap for each 4 frustum slice transformed in light =
space in one texture (aka texture atlas)

=20

Now render all gathered Shadowmap in a preprocess (Deferred Shadowing) =
-> Shadow collector

   Render each Shadowmap collected from the viewer point of view and =
store the shadow factor in a screen-sized texture

   Render Cascaded Shadowmap (Put the 4 light space matrix in constant =
register and select the right light projection to use via compare/dot =
product)

   And store the shadow factor...

=20

When you said to store shadow factor in r, g or b channel, you mean that =
the different shadow factor must not be blend together and should be =
left separated

Until they are use for lighting calculation ? So in the above =
description, spot light should be render in r channel and cascaded in g, =
then at lighting do two texture fetch ?

And I not understand why shadow collector is the z-prepass, don't you =
need to do a z-prepass before to render in the shadow collector,

You can save a lot of compare and texture fetch or I missed something ?

=20

Thanks for your help.

=20

Lagarde S=E9bastien

Software engineer

Neko entertainment

=20

=20

________________________________

De : gda...@li... =
[mailto:gda...@li...] De la part de =
Wolfgang Engel
Envoy=E9 : mercredi 4 avril 2007 14:34
=C0 : 'Game Development Algorithms'
Objet : Re: [Algorithms] Deferred shadow mask generation

=20

Oh and the shadow collector pass is the Z pre-pass ...

=20

From: gda...@li... =
[mailto:gda...@li...] On Behalf Of =
Lagarde S=E9bastien
Sent: Wednesday, April 04, 2007 4:55 AM
To: gda...@li...
Subject: [Algorithms] Deferred shadow mask generation

=20

Hello,=20

I heard that the Crytech engine2 use a specific technique they call =
"deferred shadow mask generation" for blend all shadow buffer in one =
shadow buffer

Then practice a "smart blur" on it to get soft shadows.

This mask is then reuse later to render shadow in the scene.

=20

Anyone heard about a similar technique like this or have some =
information on how to gather many shadow buffer in one ?

=20

Thank you.

=20

Lagarde S=E9bastien

Software engineer

Neko entertainment

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