Cairo graphics (RC6): Dilate image with transparent regions

[tmighty2]

Hello!

I have been following this tutorial: https://www.vbforums.com/showthread....an-Cairo-do-it as I am still trying to make a graphic appear like a paper cut out.

It does not work in my case because the object in my image is irregular.
Simply offsetting copies of the original image creates something like that:



Can somebody tell me if he knows a way to relatively easily "dilate" (I believe that is the term) such an image, or do I have to use OpenCV, ConvexHull detection and maximas?

Thank you.

[ColinE66]

If you create a blurred version of your image, and then paint that with a single colour, you should be able to use that as an outline for your actual image.

[tmighty2]

Thank you.
I feel so stupid, I don't manage it.

I tried it for 4 hours.

Can you fix my code?

Public Function CreateDilate(ByRef uSrc As cCairoSurface, ByVal uColor As Long, ByVal uDilateWidth As Long) As cCairoSurface

    Dim sBlur As cCairoSurface
    Set sBlur = uSrc.CreateSimilar(CAIRO_CONTENT_COLOR_ALPHA, , , True)
    sBlur.FastBlur 30

    With Cairo.CreateSurface(uSrc.Width * (uDilateWidth * 2), uSrc.Height * (uDilateWidth * 2)).CreateContext
        .RenderSurfaceContent sBlur, 0, 0, sBlur.Width, sBlur.Height, , 1
        .SetSourceColor uColor
        .MaskSurface .Surface
        Set CreateDilate = .Surface
    End With
    
End Function

[jpbro]

Try this code (the meat was written by Olaf, I just did some surrounding stuff and added comments to try to explain what the code is doing):

   Dim lo_SrfImage As RC6.cCairoSurface
   Dim lo_SrfBorder As RC6.cCairoSurface
   Dim b() As Byte
   Dim re As Byte
   Dim gr As Byte
   Dim bl As Byte
   
   ' Load main image
   Set lo_SrfImage = Cairo.CreateSurface(0, 0, , "C:\myimage.png")   ' Change path to path to your image
   
   ' Create blurred image surface for the border
   Set lo_SrfBorder = lo_SrfImage.GaussianBlur(15, 15)   ' Change this number to change the border width

   ' Get border colour RGB
   bl = (vbRed And &HFF0000) \ &H10000 ' Change vbRed to whatever colour you want the border to be
   gr = (vbRed And &HFF00&) \ &H100&
   re = vbRed And &HFF
   
   ' Remove transparency and change colour
   lo_SrfBorder.BindToArray b

   For y = 0 To UBound(b, 2): For x = 0 To UBound(b, 1) Step 4
         If b(x + 3, y) > 5 And b(x + 3, y) < 255 Then   'when semi-transparent (in a certain range)...
            ' Colors are stored in BGRA order
            
            b(x + 0, y) = bl
            b(x + 1, y) = gr
            b(x + 2, y) = re
            b(x + 3, y) = 255 '...set all 4 components of the whole pixel to fully opaque
         Else
            b(x + 0, y) = 0   '...set all 4 components of the whole pixel to fully transparent
            b(x + 1, y) = 0
            b(x + 2, y) = 0
            b(x + 3, y) = 0
         End If
      Next x
   Next y

   lo_SrfBorder.ReleaseArray b
   
   ' Draw original image over top border image
   lo_SrfBorder.CreateContext.RenderSurfaceContent lo_SrfImage, lo_SrfBorder.Width / 2 - lo_SrfImage.Width / 2, lo_SrfBorder.Height / 2 - lo_SrfImage.Height / 2
   
   lo_SrfBorder.DrawToDC Me.hDC  ' Draw the image with border

Should produce a result like this:

[tmighty2]

Thank you so much!!

[tmighty2]

I am trying to locate a post that is about dropshadow with RC6 / Cairo Graphics, but I don't find one.

Can somebody recommend his way of doing it?

[jpbro]

Might be better to start a new topic for this, but I recommend playing around with GaussianBlur, then convert to grayscale (using Olaf's method here), and maybe even play with the gamma/brightness/contrast using the CCairoSurface.AdjustColors method. Finally draw the shadow at an XY position offset from center and draw the main image over top at the center.

[tmighty2]

Thank you, I did that now.

[tmighty2]

You mean this one?

->

Private Sub RenderDisabledIco(CC As cCairoContext, Srf As cCairoSurface, x, y)
      CC.SetSourceColor vbWhite
      CC.MaskSurface Srf, x, y
      CC.Operator = Cairo_OPERATOR_HSL_LUMINOSITY
        CC.RenderSurfaceContent Srf, x, y
      CC.Operator = CAIRO_OPERATOR_OVER
End Sub

They greyscale functions on that page produce the following image for me which is perhaps "disabled", but not really greyscale:

[tmighty2]

Ok, I got it now, I hope.
I didn't use the right parameter for Make(...), and Y in that function should be 0, not 1.

Here is the full code now:

Public Sub MakeSemiTransparentFullyOpaqueBlack(Srf As cCairoSurface, ByVal uShadowAlpha As Byte, Optional ByVal UpperAlpha As Byte = 128)
  Dim X As Long, y As Long, b() As Byte

  Srf.BindToArray b

  For y = 0 To UBound(b, 2): For X = 0 To UBound(b, 1) Step 4
    If b(X + 3, y) > 0 And b(X + 3, y) > UpperAlpha Then 'when semi-transparent (in a certain range)...
       
       b(X + 0, y) = 0
       b(X + 1, y) = 0
       b(X + 2, y) = 0
       b(X + 3, y) = uShadowAlpha '255 = completely black/opaque 0=completely transparent, 124=halftransparent
    End If
  Next X, y
  
  Srf.ReleaseArray b
End Sub
Public Function CreateDropShadow(ByRef uSurf As cCairoSurface, ByVal uRadius As Long, ByVal uColor As Long, ByVal uAlpha As Double) As cCairoSurface

    Dim btAlpha As Byte
    btAlpha = pConvertAlpha(uAlpha)

    Dim nCopyOrigS As cCairoSurface
    Set nCopyOrigS = uSurf.CreateSimilar(CAIRO_CONTENT_COLOR_ALPHA, , , True)

    MakeSemiTransparentFullyOpaqueBlack nCopyOrigS, btAlpha, 0
  
    'debugging:
    'nCopyOrigS.WriteContentToPngFile "d:\weg\bla2.png"

    Dim nCopyOrigC As cCairoContext
    Set nCopyOrigC = nCopyOrigS.CreateContext

    Dim lRetRadius&
    lRetRadius = uRadius
 
    Set nCopyOrigS = nCopyOrigS.GaussianBlur(lRetRadius / 2, lRetRadius, False)

    Dim lWidthOrig&
    lWidthOrig = uSurf.Width
    
    Dim lWidthShadow&
    lWidthShadow = nCopyOrigS.Width

    Dim lAdd&
    lAdd = (lWidthShadow - lWidthOrig)
    
  '  Me.Caption = "Input radius: " & uRadius & ", ret radius: " & lRetRadius & ", diff: " & lAdd
    Set CreateDropShadow = nCopyOrigS
    
End Function