Generic video overlay questions?

[Alex Deucher]

On Fri, 05 Nov 2004 10:19:16 -0800, Kendall Bennett
<kendallb at scitechsoft.com> wrote:
> Hi Guys,
> 
> I have a few quick questions about overlays in general.
> 
> 1. In the XFree86 NV video driver, it looks like it does not support
> video overlays except for 16-bit and higher display modes (ie: they don't
> work for 8-bit modes). Is that a hardware limitation of the NVIDIA
> chipsets, or just something the driver does? The hardware we have worked
> with so far supports overlays in any color depth (even text modes ;-), so
> I found this rather curious.
> 
> 2. What is the point of RGB video overlay surfaces? The XVideo drivers do
> not export support for anything except YUV video overlay surfaces, but a
> lot of hardware has support for RGB overlays (with some limitations like
> no hue/contrast etc). So far I can't seem to find any good reason to
> support RGB video overlays. Is there something that they are useful for?
> 

Several Xservers have support for RGB Xv overlays (savage and radeon
come to mind).  I suppose they can be used for RGB videos or games or
whatnot that may want to use Xv.  I think snes9x or zsnes had an RGB
Xv path if I remember correctly.  Also some drivers use them for 8in24
pseudocolor overlays (mga, chips I think).

Alex

> I thought our basic X overlay support (not X video), but from what I
> understand the most common use fo X overlays is for color index overlays
> over RGB rendering, such as an OpenGL rendering context. Or do apps use
> RGB overlays too if they are available? If this is useful to apps, what
> common apps will actually make use of this?
> 
> I am trying to decide whether it is worth keeping the RGB overlay support
> we have built already and where we can hook it into the X drivers.
> 
> Thanks!
> 
> ---
> Kendall Bennett
> Chief Executive Officer
> SciTech Software, Inc.
> Phone: (530) 894 8400
> http://www.scitechsoft.com
> 
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