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comparison app/src/main/java/com/bartsent/simpleresizer/lib/LanczosKernel.kt @ 17:86740f593b6c

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Better memoization, more rational API.
author David Barts <n5jrn@me.com>
date Sun, 21 Feb 2021 22:14:07 -0800
parents b1605be35bcc
children 6607f675a5f7
comparison
equal deleted inserted replaced
16:3ed74dc0e34a 17:86740f593b6c
5 import kotlin.math.sin 5 import kotlin.math.sin
6 6
7 class LanczosKernel: ScalingKernel { 7 class LanczosKernel: ScalingKernel {
8 override val size = 3.0 8 override val size = 3.0
9 private val memory = HashMap<Double, Double>() 9 private val memory = HashMap<Double, Double>()
10 init { 10
11 memory.put(0.0, 1.0) 11 private fun sinc(x: Double): Double {
12 if (x == 0.0)
13 return 1.0
14 val pix = PI * x
15 return sin(pix) / pix
12 } 16 }
13 17
14 private fun sinc(x: Double): Double { 18 override fun weight(x: Double): Double {
19 if (abs(x) >= size)
20 return 0.0
15 val remembered = memory[x] 21 val remembered = memory[x]
16 if (remembered != null) 22 if (remembered != null)
17 return remembered 23 return remembered
18 val pix = PI * x 24 val calculated = sinc(x) * sinc(x/size)
19 val calculated = sin(pix) / pix
20 memory[x] = calculated 25 memory[x] = calculated
21 return calculated 26 return calculated
22 } 27 }
23
24 override fun weight(x: Double): Double =
25 if (abs(x) < size) sinc(x) * sinc(x/size) else 0.0
26 } 28 }