down the LCD panel rabbit hole

[brian]

On 08/10/2009 09:35 PM, Tim wrote:
> On Mon, 2009-08-10 at 19:38 -0400, brian wrote:
>> I'm also pretty confused as to why there are 2 separate display config
>> panels in the first place.
>
> System preferences - set up drivers and configuration for what your
> hardware actually is.
>
> User preferences - allows users to have custom resolutions to suit
> themselves, such as users with eyesight problems who want everything
> big.  If a user doesn't set their own preferences, the default is to
> give them the highest resolution available.

I sort of understood it that way. My confusion was mainly that the two 
resolution select lists didn't seem to correspond. I see, now, that it 
was because my xorg.conf was messed up. Or, I assume that was it.

One thing, though: when I finally got it right (see my other response) 
the resolutions selected were both different as well as being a lot 
lower than the max.

> Though, LCDs only work well at their physical resolution.  Even exact
> multiples of double or half resolution look disgustingly smudgy.  CRT
> monitors often work well at several different resolutions, they don't
> have 1:1 mapping of graphics pixels to the dots of screen phosphors.

Which would explain why it was so blurry earlier. It looked pretty 
miserable.

> You also mentioned frame rates.  It's usual that LCD panels only work at
> one frame rate (60 Hz being common), compared to CRTs which often work
> across a few different rates.  Most graphics cards have an array of
> different screen sizes and frame rates, with there being combinations of
> some of them that they cannot do (e.g. it may do high resolution *or*
> fast screen rates).  If your card only offers your desired resolution at
> a different frame rate that your monitor users, you can't use that
> screen mode.  That's why some people find that their desired resolution
> is unavailable to them.

The manual for this panel lists:

Mode, H Freq. (kHz), V Freq. (Hz), Pixel Clock (MHz), Sync Polarity (H/V)

640 x 350 	31.47 	70.09 	25.18 	+/-
640 x 400 	31.47 	70.09 	25.18 	-/+
640 x 480 	31.47 	59.94 	25.17 	-/-
640 x 480 	31.50 	75.00 	31.5 	-/-
720 x 400 	31.47 	70.08 	28.32 	-/+
800 x 600 	37.88 	60.32 	40.00 	+/+
800 x 600 	46.880 	75.00 	49.50 	+/+
1024 x 768 	48.36 	60.00 	65.00 	-/-
1024 x 768 	60.02 	75.03 	78.75 	+/+
1152 x 864 	67.50 	75.00 	108.00 	+/+
1280 x 1024 	63.98 	60.02 	108.00 	+/+
1280 x 1024 	79.98 	75.02 	135.00 	+/+
1920 x 1080-R 	66.587 	59.934 	138.50 	+/-
1920 x 1080 	55.62 	49.92 	141.50 	-/+

I'd come across someone else's xorg.conf for use with this same LCD. 
However, their numbers (eg. dot clock) were slightly different. And I 
was stumped as to where xorg.conf's "HTimings hdisp hsyncstart hsyncend 
htotal" numbers came from. Rather than blindly follow along with this 
person's config, I eventually found a reference to the cvt utility. I ran:

cvt 1920 1080 55.62

... to get those figures.

This is just for posterity in case someone else needs the info.

Thanks for the reply, btw.