# Trianglify Algorithm

Hi,

I found those two nice websites, which generates nice background patterns, called “trianglify”. https://trianglify.io or http://qrohlf.com/trianglify/ - Does someone did some work on something like that in Xojo? What could be the logic behind?

well trianglify has source code you can download & peruse
its in JavaScript but …

Sounds like you need a method with a loop which generates a random coordinate next to the existing ones and fills a polygon with a color moving from one to the other color. Should be doable in Xojo.

Another name for it is Tesselation or Delaunay triangulation. Check here. Gives you some basics behind algorithms.

Some code in VB:

[code]ajoute ce code dans un module
Option Explicit

'Points (Vertices)
Public Type dVertex
x As Long
y As Long
z As Long
End Type

'Created Triangles, vv# are the vertex pointers
Public Type dTriangle
vv0 As Long
vv1 As Long
vv2 As Long
End Type

'Set these as applicable
Public Const MaxVertices = 500
Public Const MaxTriangles = 1000

'Our points
Public Vertex(MaxVertices) As dVertex

'Our Created Triangles
Public Triangle(MaxTriangles) As dTriangle

Private Function InCircle(xp As Long, yp As Long, x1 As Long, y1 As Long, x2 As Long, y2 As Long, x3 As Long, y3 As Long, ByRef xc, ByRef yc, ByRef r) As Boolean
'Return TRUE if the point (xp,yp) lies inside the circumcircle
'made up by points (x1,y1) (x2,y2) (x3,y3)
'The circumcircle centre is returned in (xc,yc) and the radius r
'NOTE: A point on the edge is inside the circumcircle

Dim eps As Double
Dim m1 As Double
Dim m2 As Double
Dim mx1 As Double
Dim mx2 As Double
Dim my1 As Double
Dim my2 As Double
Dim dx As Double
Dim dy As Double
Dim rsqr As Double
Dim drsqr As Double

eps = 0.000001

InCircle = False

If Abs(y1 - y2) < eps And Abs(y2 - y3) < eps Then
MsgBox “INCIRCUM - F - Points are coincident !!”
Exit Function
End If

If Abs(y2 - y1) < eps Then
m2 = -(x3 - x2) / (y3 - y2)
mx2 = (x2 + x3) / 2
my2 = (y2 + y3) / 2
xc = (x2 + x1) / 2
yc = m2 * (xc - mx2) + my2
ElseIf Abs(y3 - y2) < eps Then
m1 = -(x2 - x1) / (y2 - y1)
mx1 = (x1 + x2) / 2
my1 = (y1 + y2) / 2
xc = (x3 + x2) / 2
yc = m1 * (xc - mx1) + my1
Else
m1 = -(x2 - x1) / (y2 - y1)
m2 = -(x3 - x2) / (y3 - y2)
mx1 = (x1 + x2) / 2
mx2 = (x2 + x3) / 2
my1 = (y1 + y2) / 2
my2 = (y2 + y3) / 2
xc = (m1 * mx1 - m2 * mx2 + my2 - my1) / (m1 - m2)
yc = m1 * (xc - mx1) + my1
End If

dx = x2 - xc
dy = y2 - yc
rsqr = dx * dx + dy * dy
r = Sqr(rsqr)
dx = xp - xc
dy = yp - yc
drsqr = dx * dx + dy * dy
If drsqr <rsqr Then InCircle True

End Function
Private Function WhichSide(xp As Long, yp As Long, x1 As Long, y1 As Long, x2 As Long, y2 As Long) As Integer
'Determines which side of a line the point (xp,yp) lies.
'The line goes from (x1,y1) to (x2,y2)
'Returns -1 for a point to the left
’ 0 for a point on the line
’ +1 for a point to the right

Dim equation As Double

equation = ((yp - y1) * (x2 - x1)) - ((y2 - y1) * (xp - x1))

If equation > 0 Then
WhichSide = -1
ElseIf equation = 0 Then
WhichSide = 0
Else
WhichSide = 1
End If

End Function

Public Function Triangulate(nvert As Integer) As Integer
'Takes as input NVERT vertices in arrays Vertex()
'Returned is a list of NTRI triangular faces in the array
'Triangle(). These triangles are arranged in clockwise order.

Dim Complete(MaxTriangles) As Boolean
Dim Edges(2, MaxTriangles * 3) As Long
Dim Nedge As Long

'For Super Triangle
Dim xmin As Long
Dim xmax As Long
Dim ymin As Long
Dim ymax As Long
Dim xmid As Long
Dim ymid As Long
Dim dx As Double
Dim dy As Double
Dim dmax As Double

'General Variables
Dim i As Integer
Dim j As Integer
Dim k As Integer
Dim ntri As Integer
Dim xc As Double
Dim yc As Double
Dim r As Double
Dim inc As Boolean

'Find the maximum and minimum vertex bounds.
'This is to allow calculation of the bounding triangle
xmin = Vertex(1).x
ymin = Vertex(1).y
xmax = xmin
ymax = ymin
For i = 2 To nvert
If Vertex(i).x < xmin Then xmin = Vertex(i).x
If Vertex(i).x > xmax Then xmax = Vertex(i).x
If Vertex(i).y < ymin Then ymin = Vertex(i).y
If Vertex(i).y > ymax Then ymax = Vertex(i).y
Next i
dx = xmax - xmin
dy = ymax - ymin
If dx > dy Then
dmax = dx
Else
dmax = dy
End If
xmid = (xmax + xmin) / 2
ymid = (ymax + ymin) / 2

'Set up the supertriangle
'This is a triangle which encompasses all the sample points.
'The supertriangle coordinates are added to the end of the
'vertex list. The supertriangle is the first triangle in
'the triangle list.

Vertex(nvert + 1).x = xmid - 2 * dmax
Vertex(nvert + 1).y = ymid - dmax
Vertex(nvert + 2).x = xmid
Vertex(nvert + 2).y = ymid + 2 * dmax
Vertex(nvert + 3).x = xmid + 2 * dmax
Vertex(nvert + 3).y = ymid - dmax
Triangle(1).vv0 = nvert + 1
Triangle(1).vv1 = nvert + 2
Triangle(1).vv2 = nvert + 3
Complete(1) = False
ntri = 1

'Include each point one at a time into the existing mesh
For i = 1 To nvert
Nedge = 0
'Set up the edge buffer.
'If the point (Vertex(i).x,Vertex(i).y) lies inside the circumcircle then the
'three edges of that triangle are added to the edge buffer.
j = 0
Do
j = j + 1
If Complete(j) <> True Then
inc = InCircle(Vertex(i).x, Vertex(i).y, Vertex(Triangle(j).vv0).x, Vertex(Triangle(j).vv0).y, Vertex(Triangle(j).vv1).x, Vertex(Triangle(j).vv1).y, Vertex(Triangle(j).vv2).x, Vertex(Triangle(j).vv2).y, xc, yc, r)
'Include this if points are sorted by X
'If (xc + r) < Vertex(i).x Then
'complete(j) = True
'Else
If inc Then
Edges(1, Nedge + 1) = Triangle(j).vv0
Edges(2, Nedge + 1) = Triangle(j).vv1
Edges(1, Nedge + 2) = Triangle(j).vv1
Edges(2, Nedge + 2) = Triangle(j).vv2
Edges(1, Nedge + 3) = Triangle(j).vv2
Edges(2, Nedge + 3) = Triangle(j).vv0
Nedge = Nedge + 3
Triangle(j).vv0 = Triangle(ntri).vv0
Triangle(j).vv1 = Triangle(ntri).vv1
Triangle(j).vv2 = Triangle(ntri).vv2
Complete(j) = Complete(ntri)
j = j - 1
ntri = ntri - 1
End If
'End If
End If
Loop While j < ntri

'Tag multiple edges
'Note: if all triangles are specified anticlockwise then all
'interior edges are opposite pointing in direction.
For j = 1 To Nedge - 1 If Not Edges(1, j) 0 And Not Edges(2, j) 0 Then
For k = j + 1 To Nedge If Not Edges(1, k) 0 And Not Edges(2, k) 0 Then
If Edges(1, j) = Edges(2, k) Then
If Edges(2, j) = Edges(1, k) Then
Edges(1, j) = 0
Edges(2, j) = 0
Edges(1, k) = 0
Edges(2, k) = 0
End If
End If
End If
Next k
End If
Next j

'Form new triangles for the current point
'Skipping over any tagged edges.
'All edges are arranged in clockwise order.
For j = 1 To Nedge If Not Edges(1, j) 0 And Not Edges(2, j) 0 Then
ntri = ntri + 1
Triangle(ntri).vv0 = Edges(1, j)
Triangle(ntri).vv1 = Edges(2, j)
Triangle(ntri).vv2 = i
Complete(ntri) = False
End If
Next j
Next i

'Remove triangles with supertriangle vertices
'These are triangles which have a vertex number greater than NVERT
i = 0
Do
i = i + 1
If Triangle(i).vv0 > nvert Or Triangle(i).vv1 > nvert Or Triangle(i).vv2 > nvert Then
Triangle(i).vv0 = Triangle(ntri).vv0
Triangle(i).vv1 = Triangle(ntri).vv1
Triangle(i).vv2 = Triangle(ntri).vv2
i = i - 1
ntri = ntri - 1
End If
Loop While i < ntri

Triangulate = ntri
End Function[/code]