[mythtv] [PATCH] Potential display aspect ratio patch for non-4:3

[Chris Pinkham]

> On 02/02/04 11:49:31, Chris Pinkham wrote:
> > So use screen resolution and pixel ratio to determine the size of the
> > bars?
> 
> Use the physical dimensions of the screen to determine the aspect =20
> ratio.  Nothing to do with pixels.  Or, alternatively, determine DPI of =20
> X and Y separately, then figure out how many pixels you need given that =20
> DPI.  However you want to think of it.

The current code uses physical dimensions to determine aspect ratio of the
screen and I wasn't talking about changing that.  I said it was incorrectly
using that information when you ran in windowed mode because your window
might not be the same aspect ratio as the screen so the black bar size was
computed incorrectly.  I think the 2nd solution you mentioned is the one.

How about these formulas (yDPMM unused but given for reference)::

First example shown with a 1600x900 screen that's 320x180mm w/ square pixels.

	float xDPMM = pixels_wide / x_mm;          1600 / 320 = 5.0
	float yDPMM = pixels_high / y_mm;          900  / 180 = 5.0

	float x_mm_needed = y_mm * XJ_aspect;      180 * 4/3  = 240
	int   x_pix_needed = x_mm_needed * xDPMM;  240 * 5    = 1200

	1200/900  = 4/3 aspect ratio
	1200/1600 = 3/4 width of 16:9 screen.

	dispxoff += (diswpoff - x_pix_needed) / 2; (1600 - 1200) / 2 = 200;
	diswpoff =  x_pix_needed;                  1200              = 1200;

This equates with the current method of using 3/4 of the 16x9 screen's
width.

Now testing 1024x1024 non-square pixels w/ 320x180mm physical size.

	xDPMM = 1024 / 320 = 3.2000
	yDPMM = 1024 / 180 = 5.6888

	x_mm_needed  = 180 * 4/3 = 239.999 (say 240)
	x_pix_needed = 240 * 3.2 = 768

	768 / 1024 = 3/4 width of 16:9 screen.

	dispxoff += (1024 - 768) / 2 = 128;
	dispwoff = 768;

Now for my 1280x800 screen which is 332x208mm physical size (99% square pixel)

	xDPMM = 1280 / 332 = 3.8554
	yDPMM = 800  / 208 = 3.84615

	x_mm_needed  = 208 * 4/3    = 277.3326
	x_pix_needed = 277.3326 * 3.8854 = 1077.548

	1078 / 800  = ~4/3
    1078 / 1280 = ~85% of 1280x800 screen (which is accurate since it's not
	                                       16:9, but more like 14.5:9)

	dispxoff = (1280 - 1078) / 2 = 101
	dispwoff = 1078;

-- 

Chris