Graphics again.

[MichaelW]

On my system, with a 1024x768 screen, it takes only about 30 scan lines to do the update, the tearing starts when the starting scan line reaches about 740, and ends somewhere around 0.

I probably should have added that one reason for the low number of scan lines per update, beyond the lower number of pixels per row, is my 60Hz refresh rate.

[jj2007]

796/180, needed 616 (on my fast machine).
The exe hangs apparently, I have to kill it manually.

[Mark Jones]

A tear line slowly meanders down the screen on my AMD x64 4000+/XP SP3/1280x1024 with a GeForce 8600GTS. This rig should easily be able to do 100FPS. Is WaitForScanline not working as expected?

[Jimg]

Hi Mark-

No, that is what it is supposed to do.  In the title bar, it show what scan line it waited for before starting the setdibitstodevice. 
It is incremented each time by 5 scanlines, so you can see what is the optimum scan line to start the drawing operation (when the tear disappears).
Also it shows how many scanlines it took to complete the operation (as long as it doesn't exceed the a full page, it's very crude).

[NightWare]

You have may sincerest apologies for doubting you

:lol not needed, plus it's essential to not blindly trust someone else, especially in asm  :wink