From a107929cfd6545d00349cbcf364cca249787907c Mon Sep 17 00:00:00 2001
From: Jiewei Qian <qjw@wacky.one>
Date: Sun, 25 Nov 2018 22:39:43 +1100
Subject: [PATCH] add old delta locate impl

---
 delta-locate.js | 154 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 delta-locate.js

diff --git a/delta-locate.js b/delta-locate.js
new file mode 100644
index 0000000..64bad26
--- /dev/null
+++ b/delta-locate.js
@@ -0,0 +1,154 @@
+const PNG = require('pngjs').PNG
+const fs = require('fs')
+
+const mode = (array) => {
+    const map = new Map();
+    let maxFreq = 0;
+    let mode;
+
+    for(const item of array) {
+        let freq = map.has(item) ? map.get(item) : 0;
+        freq++;
+
+        if(freq > maxFreq) {
+            maxFreq = freq;
+            mode = item;
+        }
+
+        map.set(item, freq);
+    }
+
+    return mode;
+};
+
+function getPngPixels(pngBuffer) {
+    const png = PNG.sync.read(pngBuffer)
+    return {
+        depth: 4,
+        order: 'rgba',
+        width: png.width,
+        height: png.height,
+        data: Uint8ClampedArray.from(png.data)
+    }
+}
+
+function computeDelta(before, after) {
+    const delta = new Uint8ClampedArray(before.data.length)
+    for (let i = 0; i !== before.data.length / 4; ++i) {
+        const brightnessBefore = 0.2126 * before.data[4*i] + 0.7152 * before.data[4*i+1] + 0.0722 * before.data[4*i+2]
+        const brightnessAfter = 0.2126 * after.data[4*i] + 0.7152 * after.data[4*i+1] + 0.0722 * after.data[4*i+2]
+
+        delta[4*i] = Math.abs(brightnessBefore - brightnessAfter)
+        delta[4*i+1] = Math.abs(brightnessBefore - brightnessAfter)
+        delta[4*i+2] = Math.abs(brightnessBefore - brightnessAfter)
+
+        delta[4*i+3] = 255
+    }
+    return {
+        data: delta,
+        colorType: 6,
+        depth: 4,
+        width: before.width,
+        height: before.height
+    }
+}
+
+function binarize(delta, THRESHOLD = 0x40) {
+    function getXY(x, y) {
+        const pos = y * delta.width + x
+        return delta.data[4 * pos]
+    }
+
+    function binarizePixel(val) {
+        return val > THRESHOLD ? 255 : 0
+    }
+
+    const ret = new Uint8ClampedArray(delta.data.length)
+
+    // pool surrounding pixels
+    for (let y = 0; y !== delta.height; ++y) {
+        for (let x = 0; x !== delta.width; ++x) {
+            const vals = []
+            const SURROUNDING = 3
+            // get surrounding pixels
+            for (let i = -SURROUNDING; i <= SURROUNDING; ++i) {
+                for (let j = -SURROUNDING; j <= SURROUNDING; ++j) {
+                    vals.push(getXY(x+i, y+j))
+                }
+            }
+            const polledResult = Math.max(...vals)
+            const pixelPos = y * delta.width + x
+
+            ret[pixelPos * 4] = binarizePixel(polledResult)
+            ret[pixelPos * 4 + 1] = binarizePixel(polledResult)
+            ret[pixelPos * 4 + 2] = binarizePixel(polledResult)
+            ret[pixelPos * 4 + 3] = 255    // alpha channel
+        }
+    }
+
+    return {
+        data: ret,
+        colorType: 6,
+        depth: 4,
+        width: delta.width,
+        height: delta.height
+    }
+}
+
+function locate(binaryMap, GAP_THRESHOLD = 10) {
+    const {
+        data,
+        width,
+        height
+    } = binaryMap
+
+    function getXY(x, y) {
+        const pos = y * width + x
+        return data[pos * 4]
+    }
+
+    const offsets = []
+
+    // scan from right
+    for (let y = 0; y !== height; ++y) {
+        let observations = []
+        let rightPos = -1
+        let leftPos = -1
+        let rightDetected = false
+        for (let x = width - 1; x >= 0; --x) {
+            const val = getXY(x, y)
+
+            observations.push(val)
+            observations.length > GAP_THRESHOLD && observations.shift()
+
+            // check for right rect's right edge
+            if (rightPos === -1 && val === 0xff) {
+                rightPos = x
+            }
+
+            // check for left rect's left edge
+            if (   rightPos >= 0
+                && observations.length === GAP_THRESHOLD
+                && observations.filter(ob => ob === 0).length === GAP_THRESHOLD
+            ) {
+                rightDetected = true
+            }
+
+            if (rightDetected && leftPos === -1 && val === 0xff) {
+                leftPos = x
+                offsets.push(rightPos - leftPos)
+                break
+            }
+        }
+    }
+
+    // get mode of X
+    return mode(offsets)
+}
+
+module.exports = function deltaLocate(sourcePixels, knobPixels) {
+    const delta = computeDelta(sourcePixels, knobPixels)
+    const binaryDelta = binarize(delta)
+    const xPos = locate(binaryDelta)
+    return xPos
+}
\ No newline at end of file