X11 expertise on ancient HW sought... (4-plane visual (overlay) via X-server on MS-WIndows)

[David Brownlee]

On 4 June 2015 at 19:24, IMAP List Administration <lists at y42.org> wrote:
> [also posted to comp.graphics.x today]
>
> Hello Folks,
>
> I'm trying to get an application that currently uses a local display on an
> ancient DEC Alpha workstation with a (for the time) mid-to-high-end graphics
> controller (ZLX-E2) to instead use an X-server running under MS-Windows.
>
> The application is complaining that it cannot find a "4/5-bit visual". It almost
> certainly wants to use this visual for an overlay, as the application displays
> moving objects superimposed on a map.
>
> On the original hardware, xdpyinfo tells me:
>> [...]
>> supported pixmap formats:
>>     [...]
>>     depth 4, bits_per_pixel 8, scanline_pad 32
>>     [...]
>> screen #0:
>>    [...]
>>   depths (4):    8, 12, 24, 4
>>   [...]
>>   number of visuals:    21
>>   [lots of other visuals here, but no 4-plane except for the following]
>>   visual:
>>     visual id:    0x36
>>     class:    PseudoColor
>>     depth:    4 planes
>>     available colormap entries:    16
>>     red, green, blue masks:    0x0, 0x0, 0x0
>>     significant bits in color specification:    4 bits
>
> and "xprop -root" tells me:
>> [...]
>> SERVER_OVERLAY_VISUALS(SERVER_OVERLAY_VISUALS) = 0x36, 0x1, 0x0, 0x1
>
> As you can see, there seems to be exactly one overlay, whose visual id (0x36)
> corresponds to the single 4-plane visual listed by xdpyinfo.
>
> When I use the above commands to retrieve the capabilities of the MS-Windows
> X-server (Exceed, in this case), xdpyinfo does not list a 4-plane visual at all.
> "xprop" lists lots of overlays, 24 in total, all of them 8-plane visuals.
>
> The MS-Windows box is running Windows-7 (64bit) and has a Nvidia Quadro 400 GPU.
> I used the "Nvidia Control Panel" to set "Enable overlay" to "on" in the "Manage
> 3D settings" section. Also, in the Exceed X-server configuration I enabled
> "OpenGL", and within that enabled "Overlay Support" and "GLX 1.3 Support".
>
> I conclude that the MS-Windows SW/HW system (X-server, MS-Win GPU driver, GPU)
> cannot offer 4-plane visuals. However, I don't know what system component(s)
> is/are the cause the problem.
>
> I have tested VcXsrv, Reflection-X, Exceed (with 3D option), X-Win32 and even
> the ancient DEC Pathworks X-server eXcursion with no success. I'm working on
> getting an evaluation copy of PTC's MKSTools X/Server. Of the X-servers I've
> tested, Exceed seems to offer the most configuration parameters.
>
> I'm not even sure the Quadro 400 can handle 4bpp "visuals", or whatever
> MS-Windows calls them. In fact, I wonder if any modern hardware offers 4bpp
> capability. On my Linux box with a GeForce GT 430 I don't have any 4-plane
> visuals, and xprop doesn't mention any overlays either.
>
> I'm somewhat confused about where overlays fit into the X scheme. I have seen
> lots of references to overlays in an OpenGL context, however the Alpha seems not
> to have any OpenGL capability: GLX is not in the list of extentions printed by
> xdpyinfo. Can someone clear this up for me?
>
> Am I correct to assume that the GPU must support 4bpp in order for it even to be
> possible for the X-server to propagate a 4-plane visual to a client? If yes, how
> can I determine if a GPU supports 4bpp? Nvidia is very sparing with the
> information in their specs for the Quadro 400 GPU.
>
> Assuming I can find a GPU that supports/offers 4bpp, does anyone know an
> X-server product/project that can provide 4-plane overlays?

Have you tried MobaXterm?

On my Thinkpad T420s (Intel gfx) booting into Windows 7, then running
my NetBSD install in Virtual box and firing up an xterm using Moba as
the X server reports:

depths (7):   24, 1, 4, 8, 15, 16, 32

The Personal version of MobaXterm is free :)