VB.NET graphics slow compared to VB6

I have an app originally written in VB6 that draws the Mandelbrot set. I loop through each pixel in a picture control, calculate the proper color for that pixel, and set the color, doing a refresh after each line. When I converted this to .NET it drew considerably slower. If I happen to minimize the app so that it doesn't have to draw anything the speed is fine.

Here are the times I'm getting for a particular view:
VB6 3 seconds
.NET (foreground) 14 seconds
.NET (background) 2 seconds

Here's a simplified piece of the VB6 code:

VB Code:

mypicture.autoredraw = true   ' set at design time
for x = 1 to 600
  for y = 1 to 400
    iterations=calculatepoint(x,y)  ' this function is where all the heavy math happens
    mypicture.pset (x,y), colorlist(iterations)  ' there's more logic going on here, but this is the important part
  next y
  doevents
next x

And here's the VB.NET code

VB Code:

bmap = new bitmap(600,400,system.drawing.imaging.pixelformat.format24bpprgb)
mypicture.image = bmap  ' these two lines done in form.load
for x = 1 to 600
  for y = 1 to 400
    iterations=calculatepoint(x,y)  ' this function is where all the heavy math happens
    bmap.setpixel(x,y,colorlist(iterations))  ' again, this is the important part
  next y
  mypicture.refresh()
  system.windows.forms.application.doevents()
next x

Is this the correct approach to this manner of drawing? Is there something I may be missing?

Thanks,
Dennis

Quote:

---

[i]

VB Code:

bmap = new bitmap(600,400,system.drawing.imaging.pixelformat.format24bpprgb)
mypicture.image = bmap  ' these two lines done in form.load
for x = 1 to 600
  for y = 1 to 400
    iterations=calculatepoint(x,y)  ' this function is where all the heavy math happens
    bmap.setpixel(x,y,colorlist(iterations))  ' again, this is the important part
  next y
  mypicture.refresh()
  system.windows.forms.application.doevents()
next x

[/B]

---

You are calling PictureBox.refresh and Doevents 600 times!

Dude theres your problem. :)

Draw the stuff to a bitmap object in the background and then set the image property to the bitmap when its finished. That will be super fast...

VB Code:

Dim bmp as bitmap = new bitmap(...)
 
for i = ...
for j = ....
'do drawing here using the SetPixel() function of the bitmap
next j
next i
 
pic.image = bmp
...

That's an idea, although I would like to see the points as they're being calculated to some degree. Some of the really deep field views can take a long time to calculate.

I did try doing another version of this where I spawn off a thread that does the loop minus the refresh call, and the other thread calls refresh once every 1/10 second. This runs better on the wide views where total time is small, but on the deeper views it can increase the time quite a bit.

The fact that the drawing routines in VB6 take up effectively no time has me wondering if I'm using the correct set of functions / classes to do this type of drawing.

By the way, are you compiling to DEBUG or RELEASE in .net?

This can make a big difference sometimes.

Release is fast but you don't get the debug facilities, but once your program runs bug free you won't need debug mode.

I tried it both ways but it didn't seem to make a lot of difference. I did notice on one of the deeper views that it runs much faster outside of the development environment than inside, which I guess is to be expected.

Anyway, its unforgiveable to run doevents and refresh 600 times.
(IMHO :) )
Screw the user he'll have to wait for all the pixels to show up at once! :D

Actually, I did find one thing that trimmed off a couple of seconds. Rather than calling mypicture.Refresh() I called mypicture.CreateGraphics.DrawImage(bmap, 0, 0).

Thanks for your suggestions. :)