RE: [Algorithms] Depth of Field and Smoke Blurs

[Tom F. <to...@mu...>]

Yes, that works well.

The way I did my depth-of-field effect was to render the scene a second time
into a small (256x128) A8R8G8B8 texture, with the alpha channel based on the
Z value using either a vertex shader, or a 1D planar-mapped texture if using
the FFP. Alpha = 0 at the focus point, fading to 1 closer and further away.

Then blend that texture over the main view, using the texture's alpha with a
standard SRCLAPHA:INVSRCALPHA. Result - the in-focus depth is razor-sharp,
and everything else is foggy.

You have to be careful with alpha-blended effects, but otherwise it works
well. And yes, you can use lower-LoD shapes for the render to the texture.


Tom Forsyth - purely hypothetical Muckyfoot bloke.

This email is the product of your deranged imagination,
and does not in any way imply existence of the author.

> -----Original Message-----
> From: Garett Bass [mailto:gt...@st...]
> Sent: 28 February 2002 14:31
> To: GDA...@li...
> Subject: RE: [Algorithms] Depth of Field and Smoke Blurs
> 
> 
> I'm curious, on the PC, could you create the same or similar 
> destination
> alpha effect by rendering the scene into destination alpha in 
> black (or
> white) with white (or black) depth-based fog?  I'm thinking 
> the color of
> each pixel in the range of black to white would be equivalent 
> to z-based
> alpha.  I'm not familiar with the workings of destination 
> alpha, so I don't
> really have any idea whether this would work or whether it 
> could be done in
> some usefull parallel to normal rendering to make it even feasible.
> 
> Perhaps you could reduce the LOD ranges dramatically when 
> using depth of
> field, or even totally alter the LOD regions to minimize the 
> tesselation in
> unfocussed areas to make up for the extra draw time the 
> effect requires?
> 
> Garett Bass
> 
> 
> -----Original Message-----
> 
> 
> On PS2 we convert the zbuffer into one big 32-bit RGBA 
> texture, and draw
> the 8-bit green colour component into the alpha channel of our frame-
> buffer [bilinear filtering off].
> The green channel proved to be the most useful one for depth-of-field
> stuff. We then scale down our framebuffer to a quarter
> of its original area [half-size offscreen buffer blit with bilinear
> filtering on] and draw it on top of the original framebuffer
> with destination alpha testing on.
> 
> Willem
> MuckyFoot Goat Boy
> 
> 
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