Recently I've been investigating performance problems with painting in one of
my controls. I've ended up with a trivial sample which illustrates strange
behavior of Graphics.DrawIcon(...).

I made a simple form and tried to draw an icon multiple times:

private void button1_Click(object sender, EventArgs e)
{
Icon icon = Resource1.MyIcon;
Rectangle rect = new Rectangle(10, 10, 16, 16);

using (Graphics g = this.CreateGraphics())
{
for (int loop = 0; loop < 10; loop++)
{
DateTime dt1 = DateTime.Now;
for (int i = 0; i < 1000; i++)
{
g.DrawIcon(icon, rect);
}
DateTime dt2 = DateTime.Now;
TimeSpan elapsed = dt2.Subtract(dt1);
Trace.WriteLine(elapsed.TotalMilliseconds.ToString());
}
}
}

So, I draw the icon 10 000 times, measuring the time needed for each
thousand. Here is what I typically get from Trace:

578,0584
874,8992
999,8848
1171,74
1390,4648
1515,4504
1624,8128
1859,1608
2015,3928
2109,132

It seems that each new thousand of DrawIcon() operations is done noticeably
slower! If I repeat it more times, I get even worse results...
Sounds like a bug to me (maybe poor caching of something, so each time a
lookup over a bigger set of things is performed). I've also noticed that if a
make a long-running loop like this, the consumed memory slowly increases.

Any explanations?
JakubS

PS: Currently I worked around the problem by doing icon.ToBitmap() and using
DrawImage(...) instead - it is much faster.

This could be an unmanaged resource problem. I think icons have a leak
somewhere.

Anyway, if your having problems it serves you right for drawing in a
CreateGraphics call ;-).

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

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http://www.bobpowell.net/tipstricks.htm

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"JakubS" <(E-Mail Removed)> wrote in message
news:EC6CE427-3834-40D7-A4FD-(E-Mail Removed)...
> Recently I've been investigating performance problems with painting in one
> of
> my controls. I've ended up with a trivial sample which illustrates strange
> behavior of Graphics.DrawIcon(...).
>
> I made a simple form and tried to draw an icon multiple times:
>
> private void button1_Click(object sender, EventArgs e)
> {
> Icon icon = Resource1.MyIcon;
> Rectangle rect = new Rectangle(10, 10, 16, 16);
>
> using (Graphics g = this.CreateGraphics())
> {
> for (int loop = 0; loop < 10; loop++)
> {
> DateTime dt1 = DateTime.Now;
> for (int i = 0; i < 1000; i++)
> {
> g.DrawIcon(icon, rect);
> }
> DateTime dt2 = DateTime.Now;
> TimeSpan elapsed = dt2.Subtract(dt1);
> Trace.WriteLine(elapsed.TotalMilliseconds.ToString());
> }
> }
> }
>
> So, I draw the icon 10 000 times, measuring the time needed for each
> thousand. Here is what I typically get from Trace:
>
> 578,0584
> 874,8992
> 999,8848
> 1171,74
> 1390,4648
> 1515,4504
> 1624,8128
> 1859,1608
> 2015,3928
> 2109,132
>
> It seems that each new thousand of DrawIcon() operations is done
> noticeably
> slower! If I repeat it more times, I get even worse results...
> Sounds like a bug to me (maybe poor caching of something, so each time a
> lookup over a bigger set of things is performed). I've also noticed that
> if a
> make a long-running loop like this, the consumed memory slowly increases.
>
> Any explanations?
> JakubS
>
> PS: Currently I worked around the problem by doing icon.ToBitmap() and
> using
> DrawImage(...) instead - it is much faster.