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[XNA, mouse lag]: I found a fix for mouse lag, but it can't be the only one...

Started by iaminternets Feb 22, 2009 at 4:40 PM 13 replies 7.8k views

Original Post

Feb 22, 2009 at 4:40 PM

Using XNA, if the IsMouseVisible property is set to true, and an image is placed at the mouse's position according to Mouse.GetState(), the image will be lagging around 80 pixels behind the correct position of the cursor (assuming the mouse is moving at a decent speed). For games which require fast, responsive mouse-movements, this is a deal-breaker. One solution I found online was to turn off vsync. Clearly, this has solution has its downsides! How do commercial games deal with this issue? [Edited by - iaminternets on February 22, 2009 11:57:21 PM]

MJP

Feb 22, 2009 at 5:05 PM

This is nothing specific to XNA...it has to do with the fact that with D3D whenever you submit a draw call, the results aren't reflected on-screen at the time that code runs on the CPU. Instead your CPU code might be up to 2 frames ahead of what the GPU is doing, and the commands are queued up by the driver. And even if you're CPU-bound and you're not working 1 or 2 frames ahead of the GPU, you still need to wait for the the back-buffer to be flipped and presented onto the front-buffer. Ultimately you're always going to be at least frame behind the cursor, hence the lag.

If you want to try something fancy, you could always use the Raw Input API's to get unprocessed mouse input data. Be aware though that since the data won't have any processing applied (for ballistics), it will feel "weird" if you just it to move a cursor.

iaminternets

Feb 22, 2009 at 6:21 PM

Thank you; I've rated you up.

Is there no other way aside from using the Raw Input API? How do modern Windows games deal with this issue?

cyansoft

Feb 22, 2009 at 6:52 PM

Why couldn't you simply set IsMouseVisible to false and draw your own mouse cursor?

iaminternets

Feb 22, 2009 at 7:09 PM

Quote:
Original post by cyansoft
Why couldn't you simply set IsMouseVisible to false and draw your own mouse cursor?

That's exactly what I'm doing (I turned on the Windows cursor to see how bad the lag was).

Something interesting: When I turn off vsync, it appears the image is still lagging a frame or two behind the windows cursor (about 2-5 pixels as opposed to 50-100 pixels), though that level of lag is probably unavoidable.

I should have mentioned this sooner, but IsFixedTimeStep is set to false.

wingbird101

Feb 22, 2009 at 8:56 PM

I think this thread at the xna community site might help you:
http://forums.xna.com/forums/t/15035.aspx

I saw a more comprehensive thread somewhere else on their forums a while back with actual code and examples, but I couldn't find it.

cyansoft

Feb 22, 2009 at 9:11 PM

How accurate are the mouse coordinates if you turn vsync back on and set IsFixedTimeStep to true?

Sc4Freak

Feb 22, 2009 at 11:48 PM

Most commercial games that use a cursor wouldn't use a software-drawn cursor like you're using, because of the issues you mentioned. Usually they'd use a hardware cursor with a custom image applied to it. This allows for much better responsiveness.

iaminternets

Feb 22, 2009 at 11:57 PM

wingbird101:

From what I read, it seems I'd have to create XNA from within a Windows Form. If I'm going to do that, how much harder would it be to simply use SlimDX (which would give me much greater control over sound)?

cyansoft:

If I turn both vsync and fixed-length frames on, the cursor seems to be delayed the same number of pixels (about 50-100), but it also stutters.

iaminternets

Feb 23, 2009 at 9:14 PM

Have any XNA-users found a work-around?

Moe

Feb 23, 2009 at 10:05 PM

Never really noticed this in my own stuff. What exactly is it that you are trying to do that is so time/pixel critical?

iaminternets

Feb 23, 2009 at 11:18 PM

I'm working on a fast-paced real-time strategy game.

Opt7ons

Feb 23, 2009 at 11:34 PM

After looking around a bit I found this solution:

using System;using System.Drawing;using System.Windows.Forms;........../// <summary>/// This is the main class for the game/// </summary>public class Main : Microsoft.Xna.Framework.Game{    public Main()    {        Bitmap cur = new Bitmap(@"C:\Documents and Settings\Opt7ons\Desktop\cur.bmp", true);        Graphics g = Graphics.FromImage(cur);        IntPtr ptr = cur.GetHicon();        Cursor c = new Cursor(ptr);        Form.FromHandle(this.Window.Handle).Cursor = c;        this.IsMouseVisible = true;    }}

From: http://forums.xna.com/forums/p/5131/26901.aspx

Sc4Freak

Feb 24, 2009 at 2:40 AM

Yeah, that's using a hardware cursor. You should also be able to have animated cursors if that's supported by .NET - I think animated cursors have the extension .ani.

iaminternets

Feb 24, 2009 at 8:06 AM

From first glance, that certainly seems to be it!

I'll play around with it more after work. Thank you very much for finding this! :)

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