; -----------------------------
; This MUST be included!!!
; -----------------------------
lensDiameter = 60
; -----------------------------
Dim Tfm (lensDiameter * lensDiameter * 2)
Dim Org (lensDiameter * lensDiameter * 2, 3)
Dim Dest (lensDiameter * lensDiameter * 2, 3)
; -----------------------------


; -----------------------------
; Lens effect by maLi/FiNESSE,
; ported to Blitz by someone
; whose name I don't have
; anymore (sorry!), converted
; to use Read/WritePixelFast
; by blitzsupport@guildhallleisure.com
; -----------------------------

Graphics 1024, 768
backpicture = LoadImage ("back001.bmp")

SetBuffer BackBuffer()
MoveMouse GraphicsWidth () / 2, GraphicsHeight () / 2

CreateLens (lensDiameter, 15)

Repeat

Cls
TileImage backpicture

x = MouseX ()
y = MouseY ()

If x => GraphicsWidth () - lensDiameter Then x = GraphicsWidth () - lensDiameter
If y >= GraphicsHeight () - lensDiameter Then y = GraphicsHeight () - lensDiameter

DrawLens (x, y, lensDiameter)

Flip

Until KeyDown (1)

End

Function CreateLens (diameter, magnification)
r = Int (diameter / 2)
s# = Sqr# (r * r - magnification * magnification)
For y = -r To -r + (diameter)
For x = -r To r + (diameter - 1)
If (x * x + y * y) >= (s * s)
a = x
b = y
Else
z = Sqr# (r * r - x * x - y * y)
a = Int (x * magnification / z + 0.5)
b = Int (y * magnification / z + 0.5)
EndIf
Tfm (1 + (y + r) * diameter + (x + r)) = (b + r) * diameter + (a + r)
Next
Next
End Function

Function DrawLens (x, y, diameter)
LockBuffer BackBuffer ()
For i = x To (x + diameter) - 1
For j = y To (y + diameter) - 1
rgb = ReadPixelFast (i, j)
Org (cx, 1) = rgb Shr 16 And %11111111
Org (cx, 2) = rgb Shr 8 And %11111111
Org (cx, 3) = rgb And %11111111
cx = cx + 1
Next
Next
cx = 1
For i = x To (x + diameter) - 1
For j = y To (y + diameter) - 1
Dest (cx, 1) = Org (Tfm (cx), 1)
Dest (cx, 2) = Org (Tfm (cx), 2)
Dest (cx, 3) = Org (Tfm (cx), 3)
WritePixelFast i, j, Dest (cx, 3) Or (Dest (cx, 2) Shl 8) Or (Dest (cx, 1) Shl 16)
Plot (i, j)
cx = cx + 1
Next
Next
UnlockBuffer BackBuffer ()
End Function