Simulating a lower resolution on the OLPC XO Laptop
strycore at gmail.com
Tue Nov 25 16:04:24 PST 2008
Jordan Crouse a écrit :
> Bert Freudenberg wrote:
>> On 25.11.2008, at 17:37, Jordan Crouse wrote:
>>> Bert Freudenberg wrote:
>>>> On 25.11.2008, at 11:57, Strider wrote:
>>>>> I have a XO Laptop which is a nice machine machine with a high
>>>>> res display of 1200x900 pixels. The problem with this is that the
>>>>> laptop isn't powerful enugh to handle fullscreen applications at
>>>>> this resolution. If only the display could switch to a lower
>>>>> resolution things would be much better but it seems that this
>>>>> laptop only supports a single resolution.
>>>>> So I was wondering if it would be possible of simulating lower
>>>>> res at a low level, that is the xf86-video-geode driver.
>>>>> I'm not an expert in video drivers but i imagine that there are
>>>>> functions to request a pixel to be drawn on screen based on
>>>>> what's in the video ram.
>>>>> Now let's say that it's not one pixel but two that we put on
>>>>> screen, and that we draw each lines two times. That would result
>>>>> in a 600x450 resolution.
>>>>> If we do the same thing but repating the operations three times ,
>>>>> we would have a 400x300 resolution.
>>>>> Some emulators have a scale option to do such a thing and manage
>>>>> it quite well, but if we had such an option in the video driver,
>>>>> the result would be even faster !
>>>>> So what do you think about this? Is it possible ?
>>>> The Geode actually can do real upscaling (that is, scale multiple
>>>> graphics resolutions to the panel resolution), it works fine on
>>>> other machines and LCDs. But latest word is that this somehow
>>>> interacts badly with our DCON, so no-one has gotten it to work
>>>> correctly on the XO yet.
>>> Indeed. I think there is a DCON interaction happening, because the
>>> mouse gets "corrupted" during upscaling as well - and that implies
>>> that the issue is happening after the screen is constructed. The
>>> upscaling works fine on a CRT and on a "standard" TFT panel, so that
>>> is what leads me back to the DCON. Its also a long shot that the
>>> 1200x900 resolution is confusing the scaler, but I doubt it since
>>> the aspect ratio is still 4:3. I would love for other people to try
>>> the driver (it is in the latest debxo, I think); perhaps you can see
>>> the pattern that I can't.
>>>> There still may be hope, because the video upscaler can take RGB
>>>> 5:6:5 data, so in theory a lower-res 16 bpp frame buffer could be
>>>> upscaled on-the-fly (and the upscaler does 30 fps easily). But I
>>>> guess getting this to work would require a very determined X
>>>> hacker ...
>>> The RGB video overlay should just work (TM). So it would take less
>>> of a determined X hacker, and more of a determined application
>>> hacker to put all the pieces together.
>> Well, I meant that this could be used to actually provide, say, an
>> 800x600x16 mode in the driver, without having to hack applications.
>> While adapting a single app may be comparatively easy, it's still a
>> major hassle to patch each and every app. Having it in the driver
>> would make things just work (TM). But that would be a major hack,
>> don't you agree?
> So if I understand what you are getting at - you want to set up a
> single overlay over the whole screen, and render everything on that?
> Thats probably doable - you could set up a shadow framebuffer like we
> do for rotation, and hook the damage code into the video overlay. It
> might work out well, but it would preclude using the video overlay for
> anything else (such as, video). It would probably also preclude
> rotation - maybe not.
> But rather then invent fanciful ways to handle this, the efforts would
> be better spent figuring out how to fix the current driver. Mitch
> reports that the Windows driver works just fine, so clearly the bug is
> on our side.
> We need developers to start understanding how the driver works.
> Everybody with a professional interest in the X driver has moved on to
> other pastures, and OLPC desperately needs community members to pick
> up the slack.
Knowing that changing resolution on Windows XP sure brings hope to solve
this problem :)
I have installed the latest DebXO on a SD Card and xrandr shows several
choices where Ubuntu and Fedora showed only the native 1200x900.
I tried the other modes but they're all messed up. It's clearly a
problem about timings.
Here's a photo of what it looks like when I try run run Scummvm in
fullscreen mode : http://img155.imageshack.us/img155/5589/img0700qg4.jpg
I had a similar "out of sync" problem on my other laptop back when the
radeon driver had problems on my display. Windows XP had no problems
and I had a tool which allowed me to find the correct timing to add
valid ModeLines to xorg.conf. Later versions of Ubuntu corrected this
problem and I could switch resolutions without any problems. I hope the
same thing will happen with the Geode driver soon :)
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