[bmx] Interpolation by Pineapple [ 1+ years ago ]

[BlitzBot]

Title : Interpolation
Author : Pineapple
Posted : 1+ years ago

Description : Linear, cosine, cubic, and hermite interpolation functions

Code :

Code (blitzmax) Select Expand

' --+-----------------------------------------------------------------------------------------+--
'  |   This code was originally written by Sophie Kirschner (sophiek@pineapplemachine.com)   |  
'  | It is released as public domain. Please don't interpret that as liberty to claim credit |  
'  |   that isn't yours, or to sell this code when it could otherwise be obtained for free   |  
'  |                because that would be a really shitty thing of you to do.                |
' --+-----------------------------------------------------------------------------------------+--

' these functions were adapted from the interpolation algorithms described at
' http://freespace.virgin.net/hugo.elias/models/m_perlin.htm
' http://www.blitzbasic.com/codearcs/codearcs.php?code=781

SuperStrict

Import brl.math ' for interpolate_cosine

' example code
Rem
Graphics 512,512

Local pix_linear:TPixmap=CreatePixmap(128,256,PF_RGB888)
Local pix_cosine:TPixmap=pix_linear.copy()
Local pix_cubic:TPixmap=pix_linear.copy()
Local pix_hermite:TPixmap=pix_linear.copy()

Local begin_r%=0
Local begin_g%=10
Local begin_b%=32

Local end_r%=255
Local end_g%=70
Local end_b%=4

Local before_r%=0
Local before_g%=0
Local before_b%=0

Local after_r%=255
Local after_g%=255
Local after_b%=255

For Local y%=0 Until pix_linear.height
' linear
Local value!=y/Double(pix_linear.height)
Local red%=  interpolate_linear(begin_r,end_r,value)
Local green%=interpolate_linear(begin_g,end_g,value)
Local blue%= interpolate_linear(begin_b,end_b,value)
red=Min(255,Max(0,red));green=Min(255,Max(0,green));blue=Min(255,Max(0,blue))
Local rgb_linear%=red Shl 16 | green Shl 8 | blue
' cosine
red%=  interpolate_cosine(begin_r,end_r,value)
green%=interpolate_cosine(begin_g,end_g,value)
blue%= interpolate_cosine(begin_b,end_b,value)
red=Min(255,Max(0,red));green=Min(255,Max(0,green));blue=Min(255,Max(0,blue))
Local rgb_cosine%=red Shl 16 | green Shl 8 | blue
' cubic
red%=  interpolate_cubic(before_r,begin_r,end_r,after_r,value)
green%=interpolate_cubic(before_g,begin_g,end_g,after_g,value)
blue%= interpolate_cubic(before_b,begin_b,end_b,after_b,value)
red=Min(255,Max(0,red));green=Min(255,Max(0,green));blue=Min(255,Max(0,blue))
Local rgb_cubic%=red Shl 16 | green Shl 8 | blue
' hermite
red%=  interpolate_hermite(before_r,begin_r,end_r,after_r,value,0.5,0.5)
green%=interpolate_hermite(before_g,begin_g,end_g,after_g,value,0.5,0.5)
blue%= interpolate_hermite(before_b,begin_b,end_b,after_b,value,0.5,0.5)
red=Min(255,Max(0,red));green=Min(255,Max(0,green));blue=Min(255,Max(0,blue))
Local rgb_hermite%=red Shl 16 | green Shl 8 | blue
For Local x%=0 Until pix_linear.width
pix_linear.WritePixel(x,y,rgb_linear)
pix_cosine.WritePixel(x,y,rgb_cosine)
pix_cubic.WritePixel(x,y,rgb_cubic)
pix_hermite.WritePixel(x,y,rgb_hermite)
Next
Next

Local start_y%=0
Local end_y%=0
Local before_y%=0
Local after_y%=0
Local editpoint%=0

Repeat
Cls
DrawPixmap pix_linear,0,0
DrawPixmap pix_cosine,128,0
DrawPixmap pix_cubic,256,0
DrawPixmap pix_hermite,384,0
lines before_y,start_y,end_y,after_y,128,382,256
SetColor 255,255,255
DrawText "Linear",2,2
DrawText "Cosine",130,2
DrawText "Cubic",258,2
DrawText "Hermite",386,2
SetColor 128,128,128
DrawText "Linear",2,260
SetColor 255,0,0
DrawText "Cosine",2,280
SetColor 0,255,0
DrawText "Cubic",2,300
SetColor 255,255,0
DrawText "Hermite",2,320
Local modifier%=KeyDown(key_down)-KeyDown(key_up)
If KeyHit(key_left) Or KeyHit(key_right) Then editpoint=Not editpoint
If editpoint Then start_y:+modifier Else end_y:+modifier
start_y=Min(100,Max(-100,start_y))
end_y=Min(100,Max(-100,end_y))
Flip
Until KeyDown(key_escape) Or AppTerminate()

Function lines(a%,b%,c%,d%,x%,y%,w%)
For Local i%=0 Until w
Local value!=i/Double(w)
SetColor 128,128,128
Plot x+i,y+interpolate_linear(b,c,value)
SetColor 255,0,0
Plot x+i,y+interpolate_cosine(b,c,value)
SetColor 0,255,0
Plot x+i,y+interpolate_cubic(a,b,c,d,value)
SetColor 255,255,0
Plot x+i,y+interpolate_hermite(a,b,c,d,value,0.5,0.5)
Next
End Function

EndRem

' a --- b
Function interpolate_linear!(a#,b#,x!)
Return a*(1-x)+b*x
End Function
' a --- b
Function interpolate_cosine!(a#,b#,x!)
Local f!=(1-Cos(x*180))*.5
Return a*(1-f)+b*f
End Function
' a     b --- c     d
Function interpolate_cubic!(a#,b#,c#,d#,x!)
Local p#=(d-c)-(a-b)
Return p*x*x*x+((a-b)-p)*x*x+(c-a)*x+b
End Function
' a     b --- c     d
Function interpolate_hermite!(a#,b#,c#,d#,x!,tension#,bias#)
Local x2!=x*x
Local x3!=x*x2
Local xb!=(1+bias)*(1-tension)/2!
Return (2*x3-3*x2+1)*b+(((x3-2*x2+x)*(a+c))+(x3-x2)*(b+d))*xb+(3*x2-2*x3)*c
End Function

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