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Old 02 June 2010, 10:42   #1
absence
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What are the "ticks" mentioned in graphics/displayinfo.h (and .i)?

Resolutions are specified as "ticks-per-pixel" in both graphics/displayinfo.h and graphics/displayinfo.i. Apparently there are 44 ticks per pixel in "lores" both horizontally and vertically, which would mean tick frequencies of 312.125 MHz and 688.6 kHz respectively on PAL (different ones for NTSC of course). That doesn't make much sense. Does anyone know what these "ticks" are?
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Old 02 June 2010, 17:54   #2
Toni Wilen
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Displayinfo also mentions "mouse tick" (Internal mouse speed factor or something?).

I guess tick values are number of "mouse ticks" needed to move mouse one horizontal and vertical pixel. Keeps (nearly) same mouse speed in all display modes without losing required 1:1 mouse coordinates to display coordinates mapping.
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Old 03 June 2010, 01:34   #3
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The "mouse ticks" weren't introduced yet in 2.0, so it would be strange to base display resolutions on it. Besides, the resolution returned for "lores" PAL is 44x44, and while I don't know exactly how many DPIs you get with a common Amiga setup, multiplying the value by 44 results in a mouse resolution that would rival many modern gaming mice.
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Old 03 June 2010, 08:17   #4
Toni Wilen
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I didn't mean it is any kind of mouse DPI, it could be some "randomly" chosen scaling value (probably already in 2.0 or older but not documented).

For example: MouseXPixelDelta = MouseXDelta * mousetickx / 44; (simplified, no remainder calculation)
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Old 03 June 2010, 09:28   #5
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Ah sorry, I misunderstood. I've done an unscientific experiment to test this theory: Started WinUAE 2.1.0 with a PAL configuration (which has 44 "ticks-per-pixel" in the vertical direction), loaded Workbench 3.1 and set mouse speed to the slowest in Prefs. Then I measured how far the mouse has to be moved to move the pointer from the top to the bottom of the screen. Then I changed to an NTSC configuration (which has 52 "ticks-per-pixel" in the vertical direction) in WinUAE, restarted and did the same thing. This time there was less movement needed.

This would seemingly rule out mouse scaling, except I unfortunately don't have a real Amiga to test with (it's dead ). I guess you're the right person to tell if one would be needed though, or if the tests in WinUAE are valid.
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Old 03 June 2010, 11:18   #6
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I guess it could be used for correlation between the pixel aspect of your screen and that of your printer.
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Old 03 June 2010, 12:53   #7
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It could be used for anything related to aspect ratio, e.g. making sure the result of drawing a circle or square is something that looks like a circle or square. The question is what kind of ticks there are 44 of in a pixel. But I guess they could simply have been made up.
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Old 03 June 2010, 13:28   #8
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One guess is a base ratio of 11:13 (you can't express this ratio with smaller integers) for a lowres NTSC pixel, and the values are then multiplied by 4 to 44:52 in order to make for the super hires resolutions, where f.ex a 1280*200 NTSC screen would have a pixel aspect of 11:52. The ticks are most likely just a made-up generic unit.
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Old 03 June 2010, 15:32   #9
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Yes, that sounds sensible. If the units are just made up, it's still a bit strange to call them "ticks per pixel" rather than just "ticks", but as there seems to be no common knowledge or documentation about this, it's hard to guess the reason.
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