Point Method [resolved]

[UTGrim]

I need to know the value of a pixel in a picture, but the picture can't be visible.

I tried the Point Method on an invisible PictureBox control. It returned -1, which according to MSDN Help means that the x and/or y coordinates were out of range.

Does anybody know anything that could help me with this? Thanks!

[dglienna]

Look in the GAMING section of VBF. I think you want a BackBuffer.

[NoteMe]

How do you load the picture. Is it on an OffscreenDC? Or in a picture ox that is not visible or what?

[UTGrim]

How do you load the picture. Is it on an OffscreenDC? Or in a picture ox that is not visible or what?

I used the LoadPicture function on a PictureBox like this:

picGuide.Visible = False
Set picGuide.Picture = LoadPicture(App.Path + "\guide.bmp")

Sorry, I don't know what an OffscreenDC is, but I loaded then picture on an invisible PictureBox. I couldn't find anything similar to the Point Method on a picture object.

[NoteMe]

I have never tried this in VB, and I don't have it installed. But you can try the GetPixel API. If that doesn't work, I think you have to load it to an offscreen DC, as I think dglienna ment.


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[StoneTheCrows]

I have a small App that does something similar to this where PictureBox.Visible is False. In it I just need to know whether each pixel is Zero or Greater than Zero.

 
Public Sub CheckPixels(ByVal Filename as String)
	Picture1.Picture = LoadPicture(App.Path & Filename)
	For x = 0 To Picture1.Width
		For y = 0 To Picture1.Height
			 If Picture1.Point(x, y) = 0 Then
				 ' Do Something
			 Else
				 ' Do soemthing else
			 End If
		Next y
	Next x
	Picture1.Picture = Nothing
End sub

This seems to work just fine. Is there something I'm missing?

[StoneTheCrows]

OK, so I'm an idiot, my method worked fine because if the point method returns -1 then clearly it's not 0, which is all my code was looking for. So I tried the same thing but evaluating the actual value of each point in the picture box and sure enough it does return -1 in some cases. I think the reason is that the point has not been assigned a value as yet, probably because the loaded picture does not fill the picture box.

I guess the solution to UTGrims problem is to trap for -1 and deal with it accordingly, either ignore it because it's not in the Image, or deal with it as a Black (0 Value) Pixel.

[trisuglow]

An easy solution that you may be able to use is to have the Picture's Visible property set to True, but locate it off the edge of the form, or hide it behind another control.

[brucevde]

In order for the Point method to work the point/pixel must be visible, ie visible to the user, unless the AutoRedraw property is set to True.

[UTGrim]

Thank you, everybody that helped me! I tried the GetPixel API, but it wasn't what I wanted. What worked was brucevde's idea. Thanks!