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annotate 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
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e8059b166de1 Lanczos works, but is painfully slow.
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1 package com.bartsent.simpleresizer.lib
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3 import kotlin.math.PI
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4 import kotlin.math.abs
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5 import kotlin.math.sin
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7 class LanczosKernel: ScalingKernel {
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8 override val size = 3.0
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9 private val memory = HashMap<Double, Double>()
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11 private fun sinc(x: Double): Double {
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12 if (x == 0.0)
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13 return 1.0
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14 val pix = PI * x
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15 return sin(pix) / pix
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16 }
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18 override fun weight(x: Double): Double {
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19 if (abs(x) >= size)
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20 return 0.0
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21 val remembered = memory[x]
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22 if (remembered != null)
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23 return remembered
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24 val calculated = sinc(x) * sinc(x/size)
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25 memory[x] = calculated
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26 return calculated
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27 }
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28 }