SetCanvasAlpha ( canvas_number, alpha )

This works just fine on every computer I have tested it on. I modified johnno56 demo to demonstrate how it works.

This adds an extra canvas to johnno's original demo which is just used as a grey background. Canvas #1 is where the shape is drawn. Go down to line 118 to see where the SetCanvasAlpha code is being used. When the shape is finished drawing it will ask you to press 1 or 2 to see what low alpha and high alpha look like.

   '===========================================================================
   '3D Surface Plot
   'From "Microcomputer Graphics Techniques and Applications" by Donald Hearn
   'Ported To PB by Dave Navarro (dave@powerbasic.com)
   '===========================================================================
   'Converted to sdlBAS, and colorized by Andres Amaya Jr
   '===========================================================================
   'Converted to RCBasic by Johnno56 - 27-Aug-2019
   '===========================================================================
   sw = 960
   sh = 720
   title$ = "3D Surface Plot"
   WindowOpen(1,title$,WINDOWPOS_CENTERED,WINDOWPOS_CENTERED,sw,sh,0)
   CanvasOpen(1,sw,sh,0,0,sw,sh,1)
   CanvasOpen(2,sw,sh,0,0,sw,sh,0)
   Canvas(2)
   SetColor(RGB(100,100,100))
   BoxFill(0,0,sw,sh)
   Canvas(1)
   cx = int(sw / 2)
   cy = int(sh / 2)
   fx = cx - 30
   fy = cy - 114
   oldx = 0
   oldy = 0
   colours = 48
   dim pal[colours]
   pal[0]  = rgb(HexVal("00"), HexVal("00"), HexVal("FF"))
   pal[1]  = rgb(HexVal("20"), HexVal("00"), HexVal("FF"))
   pal[2]  = rgb(HexVal("40"), HexVal("00"), HexVal("FF"))
   pal[3]  = rgb(HexVal("60"), HexVal("00"), HexVal("FF"))
   pal[4]  = rgb(HexVal("80"), HexVal("00"), HexVal("FF"))
   pal[5]  = rgb(HexVal("A0"), HexVal("00"), HexVal("FF"))
   pal[6]  = rgb(HexVal("C0"), HexVal("00"), HexVal("FF"))
   pal[7]  = rgb(HexVal("E0"), HexVal("00"), HexVal("FF"))
   pal[8]  = rgb(HexVal("FF"), HexVal("00"), HexVal("FF"))
   pal[9]  = rgb(HexVal("FF"), HexVal("00"), HexVal("E0"))
   pal[10] = rgb(HexVal("FF"), HexVal("00"), HexVal("C0"))
   pal[11] = rgb(HexVal("FF"), HexVal("00"), HexVal("A0"))
   pal[12] = rgb(HexVal("FF"), HexVal("00"), HexVal("80"))
   pal[13] = rgb(HexVal("FF"), HexVal("00"), HexVal("60"))
   pal[14] = rgb(HexVal("FF"), HexVal("00"), HexVal("40"))
   pal[15] = rgb(HexVal("FF"), HexVal("00"), HexVal("20"))
   pal[16] = rgb(HexVal("FF"), HexVal("00"), HexVal("00"))
   pal[17] = rgb(HexVal("FF"), HexVal("20"), HexVal("00"))
   pal[18] = rgb(HexVal("FF"), HexVal("40"), HexVal("00"))
   pal[19] = rgb(HexVal("FF"), HexVal("60"), HexVal("00"))
   pal[20] = rgb(HexVal("FF"), HexVal("80"), HexVal("00"))
   pal[21] = rgb(HexVal("FF"), HexVal("A0"), HexVal("00"))
   pal[22] = rgb(HexVal("FF"), HexVal("C0"), HexVal("00"))
   pal[23] = rgb(HexVal("FF"), HexVal("E0"), HexVal("00"))
   pal[24] = rgb(HexVal("FF"), HexVal("FF"), HexVal("00"))
   pal[25] = rgb(HexVal("E0"), HexVal("FF"), HexVal("00"))
   pal[26] = rgb(HexVal("C0"), HexVal("FF"), HexVal("00"))
   pal[27] = rgb(HexVal("A0"), HexVal("FF"), HexVal("00"))
   pal[28] = rgb(HexVal("80"), HexVal("FF"), HexVal("00"))
   pal[29] = rgb(HexVal("60"), HexVal("FF"), HexVal("00"))
   pal[30] = rgb(HexVal("40"), HexVal("FF"), HexVal("00"))
   pal[31] = rgb(HexVal("20"), HexVal("FF"), HexVal("00"))
   pal[32] = rgb(HexVal("00"), HexVal("FF"), HexVal("00"))
   pal[33] = rgb(HexVal("00"), HexVal("FF"), HexVal("20"))
   pal[34] = rgb(HexVal("00"), HexVal("FF"), HexVal("40"))
   pal[35] = rgb(HexVal("00"), HexVal("FF"), HexVal("60"))
   pal[36] = rgb(HexVal("00"), HexVal("FF"), HexVal("80"))
   pal[37] = rgb(HexVal("00"), HexVal("FF"), HexVal("A0"))
   pal[38] = rgb(HexVal("00"), HexVal("FF"), HexVal("C0"))
   pal[39] = rgb(HexVal("00"), HexVal("FF"), HexVal("E0"))
   pal[40] = rgb(HexVal("00"), HexVal("FF"), HexVal("FF"))
   pal[41] = rgb(HexVal("00"), HexVal("E0"), HexVal("FF"))
   pal[42] = rgb(HexVal("00"), HexVal("C0"), HexVal("FF"))
   pal[43] = rgb(HexVal("00"), HexVal("A0"), HexVal("FF"))
   pal[44] = rgb(HexVal("00"), HexVal("80"), HexVal("FF"))
   pal[45] = rgb(HexVal("00"), HexVal("60"), HexVal("FF"))
   pal[46] = rgb(HexVal("00"), HexVal("40"), HexVal("FF"))
   pal[47] = rgb(HexVal("00"), HexVal("20"), HexVal("FF"))
   rho = 45
   scale = 1020
   theta = 1
   snt = Sin(Theta)
   cst = Cos(Theta)
   Phi = 1.0
   snp = Sin(Phi)
   csp = Cos(Phi)
   tx = 450
   ty = 485 'x & y translates
   ClearCanvas
   For x = -15 To 15 Step 0.125
    flag = 0
    x2 = x * x
    For y = -15 To 15 Step 0.125
    xy2 = (x2 + y * y) / 20
    z = 3.1 * Cos(xy2)
    xe = -x * snt + y * cst
    ye = -x * cst * csp - y * snt * csp + z * snp
    ze = -x * snp * cst - y * snt * snp - z * csp + Rho
    sx = Scale * xe / ze
    sy = Scale * ye / ze
    ix = Int(sx + tx)
    iy = sh - Int(sy + ty)
    colr = (Int(Sqrt((fx - ix) * (fx - ix) + 4.3 * (fy - iy) * (fy - iy)) / 15) + 7) Mod 48
    If flag = 0 Then
    setColor(pal[colr])
    Pset(ix, iy)
    flag = 1
    oldx = ix
    oldy = iy
    Else
    setColor(pal[colr])
    Line (oldx, oldy, ix, iy)
    oldx = ix
    oldy = iy
    End If
    Next
    update()
   next
   
   
   '------------- Set Canvas Alpha Demo ---------------------
   a = 255
   
   SetColor(RGB(255,255,255))
   Locate(0,0)
PrintS("PRESS 1 FOR LOW ALPHA")
PrintS("PRESS 2 FOR HIGH ALPHA")
   
   While Not Key(K_ESCAPE)
If Key(K_1) Then
a = 50
ElseIf Key(K_2) Then
a = 255
End If
SetCanvasAlpha(1, a)
Update()
Wend
   
   end

n00b,johnno56,

I am too foolish. Thanks.

ok

I want to ask one question. How to do the following operation? Thanks.