I've given this some thought, too. Here's how I was going to do it:

1) Always draw the mouse cursor itself to the front buffer.

2) Use dirty rectangle when you draw it. That means before you blt, you capture the pixels that you're about to overwrite. You blt the saved pixels back down to erase the image.

3) Use a "front buffer changed" flag; every time you Flip(), you set the flag (using InterLockedIncrement(), for thread safety). When you go to erase the mouse, if the flag is set, you don't Blt the saved pixels back down (they're old). Whenever you're done drawing the mouse, if the flag is set, you clear it (InterlockedDecrement).

4) The mouse drawing thread sits and waits for 2 things to happen - either an incoming WM_MOUSEMOVE, or a flag set by the primary thread, telling him that the backbuffer's just been Flip()ed. You need the flag because without it, when your FPS is high, your mouse cursor will vanish whenever it stops moving.

This is just off the top of my head (haven't written any code yet), so if it doesn't work, save me some time and tell me why.

Mason McCuskey
Spin Studios
www.spin-studios.com

[This message has been edited by mason (edited October 05, 1999).]

I'm looking to run my mouse code in a separate thread, similar to UO, so that it's smooth even when the frame rate drops off a bit. I have a fairly reasonable idea of how it is to be done, but I'm interested in hearing from anyone who has done this or has thoughts about good ways to do it. If you have code snippets, even better. Obviously simply getting WM_MOUSEMOVE messages and updating the cursor is not too difficult, but does anyone have any smart ideas for dealing with page flips, etc?

Thanks!

Starwynd

Thanks for the reply. Actually, I've tried doing it like this, but the major problem is that there's usually a delay between the page being flipped and the mouse cursor being redrawn on the primary surface, which produces a slight but noticeable flicker. My current method is that when I'm page flipping, I redraw the cursor on the back buffer before flipping (first capturing that data behind it), then after the flip I redraw the initial dirty rectangle on the back surface. It works, but it requires using 2 dirty rectangles, and makes the code itself pretty messy unfortunately. This is what led me to ask the question in the first place.

Regards

Starwynd