Blinking cursor ...

Posted on 1999-01-15
Last Modified: 2013-12-03
I have a graphic application, with moving objects on a surface. I uppdate the objects with the BitBlt function.
But my cursor blinks when i put it over the objects. How can i avoid this ?
Question by:AndersCarlsson
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LVL 14

Expert Comment

ID: 1418808
I think, you can't(windows display you Image, after that
restore cursor). Other way(wuth same result!):
Hide Cursor, BitBlt, Restore Cursor.

Author Comment

ID: 1418809
Yes Alex!
Same result. ShowCursor(FALSE), BitBlt ShowCursor(TRUE) gives blinking also.
Any other suggestions ?
LVL 31

Expert Comment

ID: 1418810
I think a non-blinking cursor above changing backgrounds is only possible with default cursors, which are usually handled by the graphics card.
Am I right ???
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LVL 14

Expert Comment

ID: 1418811
New idea! Read Bar with cursor(from Screen), place to you Image,
BitBlt! Size of Bar depends from size of Cursor, of course!

Author Comment

ID: 1418812
No , the system cursor also blinks!


Author Comment

ID: 1418813
Read Bar ..?
What is that?
Help me with some code please.

LVL 14

Expert Comment

ID: 1418814
dc = GetDC(NULL); Get Dc of Screen
mdc = CreateCompatibleDC(dc); //create comp(or use dc of you
BitBlt(mdc,x, y, x+nWidth, y + nHeight,dc,0,0,SRCCOPY);
//where x, y, ..: coordinates of you Blinking Cursor
ReleaseDC(NULL, dc); //rekease dc of Screen

LVL 22

Accepted Solution

nietod earned 100 total points
ID: 1418815
There are two fixes to this.  

First, the most common solution is to not update the portions of the screen that aren't changing.  If you are BitBlt() a new image to the entire window when only one little part is changing, that will cause the problem much more frequently.  What you should do in this case is track what portions have changed and to repaint only those portions.  This will fix the blinking in most cases, but it will still happen.  But it won't happen repeatidly so it is not annoying.  If you look carefully you will see that is how most windows programs work.

The other option is to draw the cursor on the source image before you BitBlt() it to the screen.  This will totally eliminate blinking.


Expert Comment

ID: 1418816
We have a similar problem. The cursor flickers not only when it is over the updated area but also when it is below and to the right of that area. We only update the changed portion of the screen.
We noticed also that the cursor flickers only on certain graphic card chipsets (ex S3 Virge, ATI Rage Pro and i740) but not on nVidia Riva128 or TNT.
And even one graphic card MGA Matrox Millenium in a dual boot system it flickers in Win95 but not in Win NT 4.0.
LVL 22

Expert Comment

ID: 1418817
Often The cursor will often flicker when it is near the update region, even if is not directly over it. I suspect that this is because if any portion of the cursor rectangle (even if it is not actually used as part of the cursor) overlaps the update region, the cursor is hidden before the update begins and then is restored after the update ends.  

In windows 3.1 (in my experice with it anyways) the cursor used to be hidden whenever there was an update even if it was not near it, so it used to flash like crazy.  That seems to have dissapeared in 95, for me anyways.

Some platforms like Mac and Sparc maintain the cursor in hardware, this allows the program to paint to the screen at the cursor location without it affecting the cursor.  When the cursor is moved the proper painted information is displayed.  I don't know if that is ever done in the windows world, but if so it might explain why some hardware does not flicker and some does.  

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