Android Question Draw a triangle with color interpolation

Marcob

Member
Licensed User
Given x,y coordinates and color attribute of each vertex of a triangle, does exist a library able to draw the triangle filled with interpolated colors?
 

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Erel

Administrator
Staff member
Licensed User
Tested in B4J. Layout with an ImageView named ImageView1:

B4X:
Sub Process_Globals
   Private MainForm As Form
   Private xui As XUI
   Private ImageView1 As B4XView
End Sub

Sub AppStart (Form1 As Form, Args() As String)
   MainForm = Form1
   MainForm.RootPane.LoadLayout("1") 'Load the layout file.
   MainForm.Show

   Dim pnl As B4XView = xui.CreatePanel("")
   pnl.SetLayoutAnimated(0, 0, 0, 100, 100)
   Dim cvs As B4XCanvas
   cvs.Initialize(pnl)
   Dim Points As List = Array(Array As Int(50, 0), Array As Int(100, 100), Array As Int(0, 100))
   
   Dim triangle As B4XPath
   Dim p() As Int = Points.Get(0)
   triangle.Initialize(p(0), p(1))
   p = Points.Get(1)
   triangle.LineTo(p(0), p(1))
   p = Points.Get(2)
   triangle.LineTo(p(0), p(1))
   cvs.DrawPath(triangle, xui.Color_Black, True, 0)
   Dim bc As BitmapCreator
   bc.Initialize(100, 100)
   bc.CopyPixelsFromBitmap(cvs.CreateBitmap)
   Dim clrs(3) As Int = Array As Int(xui.Color_Red, xui.Color_Green, xui.Color_Blue)
   Dim argbs(3) As ARGBColor
   Dim NewColor As ARGBColor
   NewColor.a = 255
   For i = 0 To 2
       bc.ColorToARGB(clrs(i), argbs(i))
   Next
   Dim dists(3) As Float
   For y = 0 To bc.mHeight - 1
       For x = 0 To bc.mWidth - 1
           If bc.IsTransparent(x, y) = False Then
               For i = 0 To 2
                   dists(i) = CalcDistance(Points.Get(i), x, y)
               Next
               Dim total As Float = dists(0) + dists(1) + dists(2)
               NewColor.r = 0
               NewColor.g = 0
               NewColor.b = 0
               For i = 0 To 2
                   NewColor.r = NewColor.r + argbs(i).r * dists(i) / total
                   NewColor.g = NewColor.g + argbs(i).g * dists(i) / total
                   NewColor.b = NewColor.b + argbs(i).b * dists(i) / total
               Next
               bc.SetARGB(x, y, NewColor)
           End If
       Next
   Next
   ImageView1.SetBitmap(bc.Bitmap)
End Sub

Private Sub CalcDistance(From() As Int, ToX As Int, ToY As Int) As Float
   Return Power(From(0) - ToX, 2) + Power(From(1) - ToY, 2) 'Distance ^ 2
End Sub
Depends on XUI, BitmapCreator.


It is not exactly the same interpolation. Hopefully it will help you get started.
 
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