Re: Camera effects

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Mario Veraart (rioj7++at++fel.tno.nl)
Tue, 1 Dec 1998 12:51:39 +0100 (MET)

Scott Herod wrote:
>
> Can someone suggests some methods to implement the
> following effects?
>
> I draw performer objects on a canvas that has already
> been drawn on with glDrawPixels. The performer objects
> fly in front of the previously drawn image.
>
> One effect I want to achieve is to blend every thing,
> including the background, away. I've tried doing it with
> pfFog and pfEarthSky but I can't get the ESky to sit on
> top of my previous image even by setting the ESky colors
> to have 0.0f alpha value.
>
> I've tried putting a rectangular geoset in front of the
> camera and setting it's color by hand to simulate fog but
> if I also want to move the camera about I've got to move
> the geoset so that it is always in front of the camera.
> In addition I lose the depth effects of fog.
>
> The only thing that I can think of to do is adjust the
> image being drawn as the background, but that is not an
> option because of the design.

You can get the effect you want by drawing the rectangle in the post
draw function. You draw a HeadUpDisplay with only this rectangle.
If you setup a different view transformation, ortho and ranging from
-1 to 1 for x and y, it is much easier to draw the rectangle.

>
> Do I have to have channel->clear() call in a draw callback
> to see the ESky? It certainly appears so. I'd really
> like an ESky with no alpha.
clear() draws the ESky when it is attached to the channel, otherwise
it just clears with a background color of black.
For the alpha question: try a visual without an alpha plane.

>
> Second question. Any hints on creating a depth of field
> or focal length effect? I'd like to be able to animate
> adjusting the focal length of a camera.
>
> Scott Herod
> scott++at++evt.com

Mario

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