Do not display the screensaver

[Alex Deucher]

On Thu, May 20, 2010 at 12:03 AM, Cui, Hunk <Hunk.Cui at amd.com> wrote:
> Hi, Jackson & Behrmann,
>
>        What is mean about the server's internal representation is abstracted away from the driver's representation? I don't understand it. Can you particular explain it. I know the R,G,B originality values are 16 bits per channel. When the values are transfered to the driver layer, they will be dealed with through "val = (*red << 8) | *green | (*blue>>8);" because the "val" will be writen into Gamma correction RAM register (the type of hardware register: Each of the entries are made up of corrections for R/G/B. Within the DWORD, the red correction is in b[23:16], green in b[15:8] and blue in b[7:0]).
>        Why the driver is allowed to truncate? And why not be transfered by R/G/B former values. Can you know that?
>
> BTW: Behrmann, "Three one dimensional look up tables (LUT) each of 8-bit resolution would not make much sense in this scenario." Please particular explain it. Thank you for your earnest reply.
>

Different hardware has different sized CLUTs (Color LookUp Tables).
Some have 8 bit CLUTs, others may have 10 bit and others may have 16
bit.  So we store it as a CARD16 and let the driver decide how may
bits they support.

Alex

> Thanks,
> Hunk Cui
>
> -----Original Message-----
> From: Adam Jackson [mailto:ajax at nwnk.net]
> Sent: Wednesday, May 19, 2010 10:45 PM
> To: Cui, Hunk
> Cc: xorg-devel at lists.x.org
> Subject: RE: Do not display the screensaver
>
> On Wed, 2010-05-19 at 19:01 +0800, Cui, Hunk wrote:
>> Hi, Jackson,
>>       First thanks for your explanation, through the debugging, I found
>> when I start the "fade to black", the gamma values will be setup to
>> the default value (1.0), it will be transferred to the XServer. And in
>> XServer, the value will be write into the VidModeSetGamma ->
>> xf86ChangeGamma -> xf86RandR12ChangeGamma -> gamma_to_ramp (calculate
>> the RGB values) -> RRCrtcGammaSet. Now I have some difficulty. In
>> gamma_to_ramp step, I found the type of ramp value is CARD16. Why is
>> not the CARD8? For R,G,B values, it only have 256bytes RAM.
>
> X color specifications are 16 bits per channel.  If your gamma ramp is
> less precise than that, your driver is allowed to truncate, but the
> server's internal representation is abstracted away from the driver's
> representation.
>
> - ajax
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