antialiased line...

[cyborg]

in every thread there someone giving an url to a C way of draing antialiased lines but i wanna know a VB way....
im making a paint prog and i cant stand the ugly lines in the picturebox!

Please help me!

[Sastraxi]

At 2x - 10x resolution, draw your line (at 2 width to 10 width respectively). Then scale it down to 1x, your 1:1 zoom level. Doing this with StretchBlt or PaintPicture wont produce good results. Rather, do this with an anti-aliased stretch function, I'm sure you can find the source for this. There also may be just a plain old aa'd line function somewhere, if you find one let me know.

[PsyVision]

proper alised lines work by a process of getting the color value of the pixel and the four around it (above, below, left and right) then taking an average (i think this is it). so if u can use GetPixel and SetPixel ?

[Sastraxi]

You mean anti-aliased don't ya psy? Anyways they actually work the way I showed, and that's the best course of action to take, I believe...

[/\/\isanThr0p]

for just a line I believe in Psy's method
for a full rendered picture, it has to be rendered in a higher res and than downscaled.

[cyborg]

how do i get the average color then? do i have to get the rgv value or do i use bitblt to mix them?

[cyborg]

rgv=rgb

[kedaman]

rgb is a 3dvector, get the mean by for each component sum terms and divide by two. To alphablend multiply by factor a for each component in left term, 1-a for right term

[cyborg]

ok...ill try that when i get home...

[cyborg]

it didnt work out fine...

if i have drawwidth = 1 it looked pretty ok but if i set it to a higher value i could see the dots (lines) better and it looked like ****!

i think it would look better if i used setpixel instead...but if i move the mouse fast when i draw i just get dots

is there anyway to get lines with setpixel instead? even if it would slow it down?

thanks for your help

[Mad Compie]

Search the net for wu line: these kind of lines are AA.
Note that all line drawing algorithms are derivates from Jack Bresenham's basic line drawing algorithm.

Here are some links to visualize this thread...

http://freespace.virgin.net/hugo.eli...s/x_wuline.htm

A nice tutorial at: http://www.cs.unc.edu/~mcmillan/comp...re6/Lines.html

[Jotaf98]

Mad Compie, are those links to C++ examples? I'd love to see a VB implementation of this

[PsyVision]

One of thos is C++ (the one with things like int etc) the other is some freaky i dont know. A vb version shouldnt be that hard to do.

[Jotaf98]

Well, what I really need is an algorythm to draw lines... simple, non-AA lines

It's for my lights system, it's coming along pretty good but it would be better if I had a faster algorythm
Basically I find the offset for each step of the rays each light casts (each ray is just a line, it lights up things 'till it hits a wall) using trig, and then use the old linex=linex+xoffset (same thing for the y) algorythm, which is a bit slow... can anyone help?

[Mad Compie]

Here some code to apply Jack Bresenham's non-AA line algorithm:

I rewrote it from C (as seen in http://www.cs.unc.edu/~mcmillan/com...ure6/Lines.htmlmy ) to VB:

Private Sub Form_Load()
  Me.ScaleMode = vbPixels
End Sub

Public Sub lineBresenham(ByVal x0 As Integer, ByVal y0 As Integer, ByVal x1 As Integer, ByVal y1 As Integer, ByVal Color As Long)
  Dim dY       As Integer
  Dim dX       As Integer
  Dim stepX    As Integer
  Dim stepY    As Integer
  Dim Fraction As Integer
  
  dY = y1 - y0
  dX = x1 - x0
        
  If (dY < 0) Then
   dY = -dY
   stepY = -1
  Else
   stepY = 1
  End If
  If (dX < 0) Then
    dX = -dX
    stepX = -1
  Else
    stepX = 1
  End If
  dY = dY * 2
  dX = dX * 2

  Me.PSet (x0, y0), Color
  
        If (dX > dY) Then
          Fraction = dY - (dX \ 2)
          While (x0 <> x1)
            If (Fraction >= 0) Then
              y0 = y0 + stepY
              Fraction = Fraction - dX
            End If
            x0 = x0 + stepX
            Fraction = Fraction + dY
            Me.PSet (x0, y0), Color
          Wend
        Else
          Fraction = dX - (dY \ 2)
          While (y0 <> y1)
            If (Fraction >= 0) Then
              x0 = x0 + stepX
              Fraction = Fraction - dY
            End If
            y0 = y0 + stepY
            Fraction = Fraction + dX
            Me.PSet (x0, y0), Color
          Wend
        End If
End Sub

Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
  lineBresenham X, Y, X + Rnd * Me.ScaleWidth, Y + Rnd * ScaleHeight, Rnd * &HFFFFFF
End Sub 

[Jotaf98]

Thanks