Quick question - lines

Code:

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Private Declare Function LineTo Lib "gdi32" _
(ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long

Private Sub Form_Load()
    Me.AutoRedraw = True
    LineTo Me.hdc, 200, 200
End Sub

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Why will that work, but if I change it to this it doesn't print anything ?

Code:

---

Private Declare Function LineTo Lib "gdi32" _
(ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long

Private Sub Form_Load()
    Me.AutoRedraw = True
    LineTo picture1.hdc, 200, 200
End Sub

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Here is something that is interesting. This works

VB Code:

Private Sub Command1_Click()
'from a command button click event
Me.AutoRedraw = True
LineTo Picture1.hdc, 200, 200
End Sub

However, this does not

VB Code:

Private Sub Form_Load()
'from Form_Load event
Me.AutoRedraw = True
LineTo Picture1.hdc, 200, 200
End Sub

I'm not sure why, but then I've very little experience (read that as 0 (zero)) with using the LineTo API. Perhaps some graphics folks out there knows why it works in a click event, but not in a form load event.

It's all to do with the autoredraw propery. In the not working example you where setting the form object (me.) to autoredraw = true. To get the picture example working you need to use set the picture object to autoredraw = true.

Code:

---

Private Sub Form_Load()
    Me.AutoRedraw = True
    LineTo picture1.hdc, 200, 200
End Sub

---

Yes, it al has to do with AutoRedraw.
You have two possibilities:

Set AutoRedraw on for the picturebox:

Code:

---

Private Sub Form_Load()
    Picture1.AutoRedraw = True
    LineTo Picture1.hdc, 200, 200
End Sub

---

Or leave AutoRedrw off, but use the paint Event. Note that you have to set the starting point back to zero.

Code:

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Private Declare Function MoveToEx Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As Long) As Long
Private Sub Picture1_Paint()
    MoveToEx Picture1.hdc, 0, 0, 0
    LineTo Picture1.hdc, 200, 200
End Sub

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Note that I modified the definition of the MoveToEx function, because I didn't want to use the original position.
The actual declaration is:

Code:

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Private Type POINTAPI
        x As Long
        y As Long
End Type

Private Declare Function MoveToEx Lib "gdi32" Alias "MoveToEx" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As POINTAPI) As Long

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Wow, thanks guys, didn't know there was an autoredrawproperty for anything apart from the form :rolleyes: