Re: Q:Alpha plane update for blend live video with Sirius

New Message Reply Date view Thread view Subject view Author view

Rob Jenkins (robj++at++barney.reading.sgi.com)
Fri, 23 Feb 1996 08:58:51 +0000

On Feb 23, 1:18pm, HyukKee Yun (kornet) wrote:
> Subject: Q:Alpha plane update for blend live video with Sirius
> I'm programming Performer with Onyx RE2 having Sirius.
> I'm trying a blending gfx with live video, but I'cant because alpha bit plane
> is always 0xff. I can't change it.
> With IRIS-gl I have no problem. I want to know the reason.
>
> Please Mail me.
>
> sbs01316++at++soback.hana.nm.kr
> An Seongjun
> SBS, Korea
>-- End of excerpt from HyukKee Yun (kornet)

I'm not sure from you description if it's the same thing but I had a customer
recently who was blending live video/gfx using Sirius. He was using a modified
version of /usr/people/4Dgifts/examples/dmedia/video/sirius/gfxvidtovid to
blend gfx with incoming video based on the alpha channel of the gfx - any pixel
of
the gfx with alpha > 0 shows over the video input, on the resultant ( blended )
video output.

The problem was if you asked for 8 bits of multisample the blend failed and you
just got the gfx, if you went to 4 bits ms the blend succeeded and you got
video 'background' with the gfx over.

The was because on his 2RM4 system, when he asked for 8 multisamples the
gconfig
dropped the framebuffer from 12 bits/colour component RGBA to 8 bits/colour
comp RGB - so no alpha channel.

Like I say, this may not be what you're doing, but if you're using alpha to
'key' - have a look at the frame buffer config you ask for and put some
getgconfig calls in to see what you actually got.

Cheers
Rob

PS this table ( from Allan Schaffer ) is useful to have around:
Only at less-than-full screen resolution. You can not perform
antialiasing while running at 1280x1024 resolution with only 1 RM
board. At lower resolutions, though, antialiasing is available;
960x680_60, 640x512_60 and so on.

One RM is enough for:

640x512 resolution 16 samples 8 bits/component 24-bit Z
640x512 resolution 8 samples 12 bits/component 32-bit Z
960x680 resolution 8/4 samples 12 bits/component 32-bit Z
1280x1024 resolution 0 samples 12 bits/component 32-bit Z

Two RMs are enough for:

1280x1024 resolution 8 samples 8 bits/component 24-bit Z
1280x1024 resolution 4 samples 12 bits/component 32-bit Z
1600x1200 resolution 0 samples 12 bits/component 32-bit Z

Four RMs are enough for:

1280x1024 resolution 16 samples 8 bits/component 24-bit Z
1280x1024 resolution 8 samples 12 bits/component 32-bit Z
1600x1200 resolution 8 samples 8 bits/component 24-bit Z
1600x1200 resolution 4 samples 12 bits/component 32-bit Z

-- 
________________________________________________________________
Rob Jenkins, Software Support Group, Silicon Graphics UK Ltd.       
Forum 1, Station Road, Theale, Reading, UK, RG7 4SB. 
tel 01734 257736, fax 01734 257553, email robj++at++reading.sgi.com,

New Message Reply Date view Thread view Subject view Author view

This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:52:27 PDT

This message has been cleansed for anti-spam protection. Replace '++at++' in any mail addresses with the '@' symbol.