Pixels not permanent after setpixel in picturebox ?

02-07-2003, 02:37 AM

Garmour

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Pixels not permanent after setpixel in picturebox ?

I'm just curious about this.
I was setting pixels in a picture box various colours (it's actually a fractal). The box gets filled with these pixels, but if anything obscures the box (ie, if another window get focus, or I drag the picbox off screen and back again) the pixels are lost.
This also happens if I draw my 'zoom in' box over the picbox (it's just a shape control).

Now, I've cured this using bitblt (that was fun!!) but I wanted to know why the setpixel didn't permanently (during runtime) remain in the picbox ?

02-07-2003, 02:58 AM

shmoove

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AutoRedraw = True?
I put this code on a form that has AutoRedraw = True and ScaleMode = vbPixels:

Code:

Option Explicit
Private Declare Function SetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long) As Long

Private Sub Command1_Click()
    Dim i As Long, h As Long
    h = Me.ScaleHeight / 2
    For i = 0 To Me.ScaleWidth
        SetPixel Me.hdc, i, h, vbBlue
    Next i
    Me.Refresh
End Sub

and the line is permanent.
You could also put the drawing in the Paint event, set AutoRedraw to False and omit the Me.Refresh at the end.

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02-07-2003, 05:44 AM

Garmour

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haha,
From your reference to autodraw I was able to find the key word I've been missing (persistant).

It's a bit frustrating that I went to the trouble of using bitblt instead of just being able to change the autoredraw!!!

But, it's not all bad 'cause I'm going to have to use bitblt to 'animate' my colour cycling.

Thanks shmoove.

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02-07-2003, 05:46 AM

Garmour

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In fact, I must have changed the autoredraw as part of the change to bitblt without realising the reasons. Doh!!

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....but then, what would I know ?