Re: Announcing shadow rendering feature

[Daniele C. <dca...@in...>]

It is very interesting I would like to try it soon. Can I already 
download it by cvs?
If it isn't possible when will be?
Thank's
Daniele
James Walker ha scritto:
> Description
>
> The Quesa OpenGL renderer now has an option to render shadows.   It 
> produces sharp-edged shadows from any directional, spot, or point light 
> that has its cast-shadows flag set to kQ3True.  It respects the 
> casts-shadows style but not the receive-shadows style.  Translucent 
> objects do not cast shadows, nor do lines or points.
>
> Rendering with shadows can be requested by setting an object property on 
> the renderer object:
>
> 	TQ3Boolean	theFlag = kQ3True;
> 	Q3Object_SetProperty( theRenderer, kQ3RendererPropertyShadows,
> 		sizeof(theFlag), &theFlag );
>
> This option can be used with or without the per-pixel lighting option. 
> It is not intended to work with orthographic cameras.
>
>
> Hardware Requirements
>
> In order to render with shadows, your OpenGL drawing context must:
>
> 1. Be able to have a stencil buffer at least 8 bits deep, as well as a 
> depth buffer.  (This is usually not a problem.  One case where it fails 
> is the Windows software renderer.)
>
> 2. Support either OpenGL 2.0 or the GL_EXT_stencil_two_side extension.
>
> It is preferable, but not essential, to have the extensions 
> GL_EXT_stencil_wrap and GL_NV_depth_clamp as well.
>
>
> Warnings
>
> The algorithm sets the "yon" value of your camera range to infinity.  To 
> prevent surprises, it would be a good idea to set "yon" to infinity 
> yourself. While it is true that you get the best depth resolution when 
> hither is as large as possible and yon is as small as possible, it is 
> much more important to make hither as large as possible.
>
> If you are using Quesa on Windows, beware that Windows does not allow 
> setting the pixel format of a window more than once.  This means that if 
> you start rendering without shadows, and then attempt to turn on 
> shadows, it will fail, because you will not be able to get a stencil 
> buffer.  You can work around this problem by explicitly requesting a 
> stencil buffer from the start, using 
> kQ3DrawContextPropertyGLStencilBufferDepth.
>
>
> Performance
>
> Shadows require a multi-pass rendering algorithm.  The first pass 
> handles ambient light and non-shadow-casting lights, assuming there are 
> no more than 8 of them.  Then for each shadow-casting light, there is a 
> stencil marking pass followed by a lighting pass.  Naturally, this will 
> be slower than a single-pass algorithm.  There is even more of a speed 
> hit if you combine per-pixel lighting with shadows, since each lighting 
> pass will be slower.
>
> Naturally, you can improve performance by designating some lights and 
> some objects as not casting shadows.  It also helps to use the Remove 
> backfacing style when feasible, and to ensure that your TriMeshes supply 
> face normal vectors.
>
>
>
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