another BitBlt question..

he..yup, another one for ya'll! ;)
I'm getting really strange behaviour by BitBlt. I use lotsa BitBlt's
in response to the WM_MOUSEMOVE message.
It looks a little something like this:

Code:

---

BitBlt(tempDC,0,0,
                        kWindowWidth,
                        kWindowHeight,
                        hDCMono,
                        0,
                        0,
                        SRCCOPY);
                SelectObject(hDCMono,hSelectedMonoBitmap);

                BitBlt(tempDC,0,0,
                        kWindowWidth,
                        kWindowHeight(yDelta),
                        hDCMono,
                        0+ConvertToTimePoint(xDelta)+kWindowWidth,
                        0+ConvertToPoint(yDelta),
                        SRCAND);

---

In the first BitBlt, tempDC is using a bitmap of 3 times the size as
hDCMONO does, but that shoudn't matter since it's cut by the
width and height params. In the next blt hDCMono uses a monochrome BitMap by the dimension
(0,0,kWindowWidth,kWindowHeight), the same dimensions
as the previous bitmap.
Now the question is why the first of these calls take aproximatly
60-70 ms to perform while the second only takes 10-20...?!

I performed som experiments:
I created(after many experiments) a bitmap by the dimension
800*360(kWindowHeight is 500, and width 400) and selected it into tempDC before the first blt. Now it
worked real smooth, everthing took about 20 ms. Then I changed
the BitMap to be 800*370, and I was back to were I started with my 70 msec.
ohhhhhh... why is it like this!!?

I guess my real question is: what affects BitBlt's performance?

any help is greatly apriciated :)
take care
/btq

How many memory DC do you create?

Kuphryn

I create two memoryDC's and I'm getting the main window...
so I move between 3 DC's

/btq :)

I believe the performance is better when you you create the memory DC and then use BitBlt() to draw it on the window. You could also use BitBlt() to draw the bitmap on the window once and then make modification to the window directly, but that affect the program's performance.

Kuphryn

Quote:

---

I believe the performance is better when you you create the memory DC and then use BitBlt() to draw it on the window.

---

but this is exactly what I'm doing...

/btq:)

Okay. I am out of ideas.

Kuphryn

>>what affects BitBlt's performance?<<

1. Image bit depth - monochrome images will blit faster than 32 bit images.

2. Image dimensions - smaller is faster (usually). Also dimensions in powers of 2 should do better than those that are not.

3. The type of blitting operation performed will probably have an effect too; some testing of blits with the various flags may generate some detectable time differences.

If you are interested in performance (ie speed), dump gdi and go for openGL or DirectX. GDI is really only intended/useful for GUI apps, although with the faster machines available today you can make some passable 2d stuff.