Colors in Memory DC

[StuartD]

Hi there,
I'm calling the lineTo API function on memory DC created by a call to CreateCompatibleDC. After a BitBlt to a PictureBox I can only get a black line, even after doing a CreatePen and SelectObject on the memory DC for a colored pen. Line styles work but not the color. I'm doing a vbSrcCopy on the BitBlt. What am I missing?
Thanks,
StuartD.

[John G Duffy]

The CreatePen is what should set your foreground (Line) color. Here is a snippet from a routine I use to draw colored lines

Case DrawLine ' Draw a line
Dim pt as POINTAPI
If otype = ePrinter then
m = (TwipsPerInch / Printer.TwipsPerPixelX) ' determined in points
else
m = PixelsPerInch
End If
hndpen = CreatePen(oElements(X).BorderStyle, oElements(X).width, oElements(X).fgColor)
oldpen = SelectObject(picHDC, hndpen)
' Move currentx and currenty to starting position
MoveToEx picHDC, (oElements(X).X * m) * LtoRRatio, _
(oElements(X).Y * m) * TtoBRatio, pt
' draw Line
LineTo picHDC, (oElements(X).bX * m) * LtoRRatio, (oElements(X).bY * m) * TtoBRatio
' Cleanup
hndpen = SelectObject(picHDC, oldpen)
DeleteObject hndpen




John G

[StuartD]

Thanks for the response. That's more or less what I'm doing.

If you paste the code below into a new project with a Picture Box control called Picture1... Then I get a black line when I've created a red pen to draw it - I guess it is something to do with the BitBlt or the creation of the memory DC ???

Thanks,
StuartD.

Private Type POINT_TYPE
x As Long
y As Long
End Type

Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function CreateCompatibleBitmap Lib "gdi32" (ByVal hdc As Long, ByVal nWidth As Long, ByVal nHeight As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function BitBlt Lib "gdi32" (ByVal hDCDest As Long, ByVal XDest As Long, ByVal YDest As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hDCSrc As Long, ByVal XSrc As Long, ByVal YSrc As Long, ByVal dwRop As Long) As Long
Private Declare Function MoveToEx Lib "gdi32.dll" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As POINT_TYPE) As Long
Private Declare Function LineTo Lib "gdi32.dll" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Declare Function CreatePen Lib "gdi32.dll" (ByVal fnPenStyle As Long, ByVal nWidth As Long, ByVal crColor As Long) As Long
Private Declare Function DeleteObject Lib "gdi32.dll" (ByVal hObject As Long) As Long
Private Declare Function CreateSolidBrush Lib "gdi32.dll" (ByVal crColor As Long) As Long
Private Declare Function Rectangle Lib "gdi32.dll" (ByVal hdc As Long, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long



Private Sub Form_Load()
Dim hMemDC As Long

hMemDC = CreateCompatibleDC(Picture1.hdc)

If (hMemDC <> 0) Then
Dim hOldBitMap As Long

hBitMap = CreateCompatibleBitmap(hMemDC, 500, 500)

If (hBitMap <> 0) Then
Dim newPen As Long
Dim oldPen As Long
Dim pt As POINT_TYPE
Dim oldBrush As Long
Dim newBrush As Long

hOldBitMap = SelectObject(hMemDC, hBitMap)


'Clear the background

newBrush = CreateSolidBrush(RGB(255, 255, 255))

oldBrush = SelectObject(hMemDC, newBrush)

Rectangle hMemDC, 0, 0, 500, 500

SelectObject hMemDC, oldBrush

DeleteObject newBrush


'Select the Pen


newPen = CreatePen(0, 3, vbRed)
oldPen = SelectObject(hMemDC, newPen)

MoveToEx hMemDC, 10, 10, pt

LineTo hMemDC, 100, 100

'Now copy the memory DC to the real DC

BitBlt Picture1.hdc, 0, 0, 500, 500, hMemDC, 0, 0, vbSrcCopy

SelectObject hMemDC, oldPen
DeleteObject newPen

End If
End If

End Sub

[StuartD]

Oops - you need to set autoredraw on the control too...