Why do slow mouse movements skip pixels?

Discussion in 'macOS' started by ToastyX, Oct 19, 2005.

  1. ToastyX macrumors regular

    Oct 4, 2005
    Ever since I got a Mac, I noticed that slow mouse movements skip pixels when moving in a diagonal or circular motion. Why does this happen?
  2. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    I'm not saying that they don't, but in 17 years of Mac use, I've never noticed this, and I can't say I'm really seeing it when I try it right now--the pointer just seems to sort of zigzag at an angle, as it can't (or, I suppose, doesn't) move at a diagonal, only horizontally or vertically.

    Is there some particular reason this is an issue for you? How did you even notice it?
  3. mrichmon macrumors 6502a

    Jun 17, 2003
    My guess is that it is an artifact of rounding errors. The cursor can only be drawn at position X,Y where X and Y are whole numbers. To truely move the cursor along a diagonal line (other than 45 degrees) or a circle requires a continuous rather than discrete grid.

    This is exactly the same reason why diagonal lines and circles are more like steps rather than a line or circle. That is if anti-aliasing is not used.
  4. ToastyX thread starter macrumors regular

    Oct 4, 2005
    This is an issue for me because it makes freehand drawing with the mouse harder to do, and it affects accuracy in games.

    I don't know how I notice it. I just do. I can see it happening. It's obvious to me after being used to smooth mouse movement in Linux, Windows, and DOS for so long. I guess I'm just very sensitive to detail.

    I know what you mean, but that's not what I'm talking about.

    It becomes very obvious when trying to draw circles or diagonal lines in paint programs. It happens with any mouse I try, including Apple's one-button mouse, but only in Mac OS X. To demonstrate this, I tried drawing a couple of circles and a diagonal line using both a Logitech mouse and Apple's one-button mouse on both my Power Mac G5 and my Linux machine with The GIMP 1.2.5 on both machines.

    The results speak for themselves: http://www.toastyx.net/images/mouse.html

    As you can see, the problem is not with the mouse. I know the problem is not with something I have installed because I can also see it happening when booting from the Mac OS X install disc that came with my computer. I know the problem is not with my computer because later I downloaded and booted an Ubuntu live CD, and the results were similar to my Linux machine. That means the problem is with the way Mac OS X handles mouse movement, and that bothers me because it shouldn't be happening. Why does it do this? :(

    Does anyone else notice this?
  5. Josh396 macrumors 65816


    Oct 16, 2004
    Peoria/Chicago, IL
    I've noticed it a few times but it doesn't really bother me all that much. If I had to choose between the mouse not moving perfectly while using OS X or that mouse moving perfectly and using XP, I'll take OS X everytime. ;) :p
  6. mrichmon macrumors 6502a

    Jun 17, 2003
    I doubt that you mean smooth mouse movement in DOS given that MS-DOS only provided a text-based command-line interface. :)

    Interesting results.

    The aliasing problem still exists on the input side. The problem is the same as with drawing diagonal lines and is related to conversion from continuous data to discrete data. In more detail, I suspect the issue is in how the Apple mouse driver does the conversion from the device readings to the cursor movement. You can notice the effect a little more strongly if you turn on screen zooming via the accessibility preferences and zoom in a few levels by pressing command-option-+.

    I'd suggest you submit a bug report to Apple about this since it appears that their translation algorithm is less smooth than the competition. :eek:
  7. DannySmurf macrumors 6502a

    Jul 7, 2005
    Using an Intellimouse, I get results similar to your Linux ones. I don't see that problem on OSX at all. Have you installed proper drivers for the mouse you're trying to use? Or are you perhaps using the generic drivers built into the OS?
  8. ToastyX thread starter macrumors regular

    Oct 4, 2005
    Well, I meant DOS programs. :)

    I see it happening with the built-in driver as well as with Logitech's software and USB Overdrive. Perhaps they only control the built-in driver. I've read that Microsoft's driver works differently, but that requires a Microsoft mouse. I do have a Microsoft mouse laying around somewhere. Maybe I'll test it later just to see the results, but I'd rather use my Logitech mouse.
  9. Coheebuzz macrumors 6502

    Oct 10, 2005
    Nicosia, Cyprus
    I had exactly the same problem and it turned out to be a bad usb port, plug the mouse in another and see what happens. If it doesn't work it might be a corrupted driver inside the OS, i know you hate to reinstall but most of the times it takes away all problems.
  10. jayscheuerle macrumors 68020


    Looks like a information delivery problem, like the mouse in OSX isn't being sampled enough times per second.
  11. minimax macrumors 6502

    Feb 9, 2005
    I must say this REALLY is one of my major annoyances with OSX compared to XP. For me, the mouse is behaving in a rather erratic way, especially when going on and off the dock it seems to slow down and jump like it's on a rubber cord, incredibly annoying. I was thinking about making a thread of it, perhaps I will.
    Also i noticed that under OSX it seems when you move the mouse slowly it moves slower then you'd expect, while when you move it faster it really jumps from one side to the other. I tried to play with the settings of the mouse but nothing really satisfies me :(
  12. ToastyX thread starter macrumors regular

    Oct 4, 2005
    That's one of the first things I tried before I realized it was a Mac OS X problem. It happens no matter what USB port I try. Besides, if the USB port was bad, then it should have happened when booting from the Ubuntu live CD as well, but it was smooth under Linux.

    If it's a corrupted driver, then it shouldn't happen when booting from the Mac OS X install disc, but it does. Besides, I have reinstalled for other reasons, and the problem has always been there.

    That's acceleration, which isn't necessarily a problem, but many people find the mouse hard to control when the acceleration is too strong.

    From what I can tell, the built-in mouse driver seems to take the native speed of the mouse and divides it by four, then applies acceleration. If you have a 400 DPI mouse or a mouse that defaults to 400 DPI, this can be quite slow. So what do most people do? They increase the tracking speed setting. The problem is the tracking speed setting doesn't really control the tracking speed. It controls the acceleration, so when they increase the tracking speed setting, they're making the acceleration stronger, thus making the mouse harder to control. This is what many people don't like.

    The only way to control the tracking speed is to use a third-party program like USB Overdrive. Try setting the speed to 200 DPI and the acceleration to 50%. That will double the tracking speed but give you the default acceleration. I bet you'll find the mouse much easier to control. If not, play around with it and see what works best for you.
  13. minimax macrumors 6502

    Feb 9, 2005
    Hey thanks for the info and the link, gonna try it out immediately!
  14. DrNeroCF macrumors 6502

    Sep 2, 2004
    Hm... does it a little bit with a Wacom tablet... not so much though. Of course, flash smoothes everything out a lot...
  15. OutThere macrumors 603


    Dec 19, 2002
    Using a Microsoft mouse on a public iMac G4 with Photoshop CS I got this:


    Seems like there's something amiss, as, side by side with your, it looks closer to your Linux images than the mac ones.:confused:
  16. Marble macrumors 6502a


    May 13, 2003
    Tucson, AZ
    This is an irritating phenomenon. I always thought it was the surfaces I was using my mouse on (which it still might be), but it's intriguing to know that other users are experiencing similar difficulties. My Kensington likes to get stuck on axis, so when I draw a circle it takes special effort to keep the sides from becoming stepped parallel and perpendicular lines.

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