From 5a6819757ba8081801eacfe783aea457ea49a6e6 Mon Sep 17 00:00:00 2001
From: mcrcortex <18544518+MCRcortex@users.noreply.github.com>
Date: Mon, 2 Dec 2024 20:26:27 +1000
Subject: [PATCH] Very fast scanline mesher

---
 .../voxy/client/core/util/ScanMesher2D.java   | 211 +++++++++++++-----
 1 file changed, 155 insertions(+), 56 deletions(-)

diff --git a/src/main/java/me/cortex/voxy/client/core/util/ScanMesher2D.java b/src/main/java/me/cortex/voxy/client/core/util/ScanMesher2D.java
index 44a56a10..d92d4baf 100644
--- a/src/main/java/me/cortex/voxy/client/core/util/ScanMesher2D.java
+++ b/src/main/java/me/cortex/voxy/client/core/util/ScanMesher2D.java
@@ -1,10 +1,12 @@
 package me.cortex.voxy.client.core.util;
 
-public class ScanMesher2D {
+import java.util.Random;
+
+public abstract class ScanMesher2D {
     // is much faster if implemented inline into parent
-    private long[] rowData = new long[32];
-    private int[] rowLength = new int[32];//How long down does a row entry go
-    private int[] rowDepth = new int[32];//How many rows does it cover
+    private final long[] rowData = new long[32];
+    private final int[] rowLength = new int[32];//How long down does a row entry go
+    private final int[] rowDepth = new int[32];//How many rows does it cover
     private int rowBitset = 0;
 
     int currentIndex = 0;
@@ -13,12 +15,12 @@ public class ScanMesher2D {
 
     //Two different ways to do it, scanline then only merge on change, or try to merge with previous row at every step
     // or even can also attempt to merge previous but if the lengths are different split the current one and merge to previous
-    public void putNext(long data) {
-        int thisIdx = (this.currentIndex++)&31;//Mask to current row, but keep total so can compute actual indexing
+    public final void putNext(long data) {
+        int idx = (this.currentIndex++)&31;//Mask to current row, but keep total so can compute actual indexing
 
         //If we are on the zero index, ignore it as we are going from empty state to maybe something state
         // setup data
-        if (thisIdx == 0) {
+        if (idx == 0) {
             //If the previous data is not zero, that means it was not merge-able, so emit it at the pos
             if (this.currentData!=0) {
                 if ((this.rowBitset&(1<<31))!=0) {
@@ -35,59 +37,39 @@ public class ScanMesher2D {
             this.currentSum = 0;
         }
 
-        //If we are the same as last data increment
-        if (data == this.currentData) {
-            this.currentSum++;
-            //If we merge, then just continue
-            this.mergeCurrentIfPossibleOrEmit(thisIdx);
-            return;
-        }
-
-        //write out previous data
-        if (this.currentData != 0) {
-            int prev = thisIdx-1;//We need to write in the previous entry
-            this.rowDepth[prev] = 1;
-            this.rowLength[prev] = this.currentSum;
-            this.rowData[prev] = this.currentData;
-            this.rowBitset |= 1<<prev;
+        //If we are different from previous (this can never happen if previous is index 0)
+        if (data != this.currentData) {
+            //write out previous data if its a non sentinel, it is guarenteed to not have a row bit set
+            if (this.currentData != 0) {
+                int prev = idx-1;//We need to write in the previous entry
+                if ((this.rowBitset&(1<<prev))!=0) {
+                    throw new IllegalStateException();
+                }
+                this.rowDepth[prev] = 1;
+                this.rowLength[prev] = this.currentSum;
+                this.rowData[prev] = this.currentData;
+                this.rowBitset |= 1<<prev;
+            }
+
+            this.currentData = data;
+            this.currentSum = 0;
         }
+        this.currentSum++;
 
 
-        this.currentData = data;
-        this.currentSum = 1;
-
-        this.mergeCurrentIfPossibleOrEmit(thisIdx);
-    }
-
-    private boolean mergeCurrentIfPossibleOrEmit(int index) {
-        boolean isSet = (this.rowBitset&(1<<index))!=0;
+        boolean isSet = (this.rowBitset&(1<<idx))!=0;
         //Greadily merge with previous row if possible
         if (this.currentData != 0 &&//Ignore sentinel empty
                 isSet &&
-                this.rowLength[index] == this.currentSum &&
-                this.rowData[index] == this.currentData) {//Can merge with previous row
-            this.rowDepth[index]++;
+                this.rowLength[idx] == this.currentSum &&
+                this.rowData[idx] == this.currentData) {//Can merge with previous row
+            this.rowDepth[idx]++;
             this.currentSum = 0;//Clear sum since we went down
             this.currentData = 0;//Zero is sentinel value for absent
-            return true;
+        } else if (isSet) {
+            this.emitQuad(this.rowLength[idx], this.rowDepth[idx], this.rowData[idx]);
+            this.rowBitset &= ~(1<<idx);
         }
-
-        if (isSet) {
-            this.emitQuad(this.rowLength[index], this.rowDepth[index], this.rowData[index]);
-            this.rowBitset &= ~(1<<index);
-        }
-
-        return false;
-    }
-
-    private boolean attemptMerge(int index, int length, long data) {
-        if ((this.rowBitset & (1 << index)) != 0 &&//Entry in previous bitset
-                this.rowLength[index] == length &&//If previous row merged length matches current
-                this.rowData[index] == data) {//If the previous row entry data matches
-            this.rowDepth[index]++;//Increment the depth
-            return true;
-        }
-        return false;
     }
 
     //Emits quads that exist at the mask pos and clear
@@ -95,7 +77,7 @@ public class ScanMesher2D {
         {//Emit quads that cover the previous indices
             int rowSet = this.rowBitset&msk;
             while (rowSet!=0) {//Need to emit quads that would have skipped, note that this does not include the current index
-                int index = Integer.numberOfLeadingZeros(rowSet);
+                int index = Integer.numberOfTrailingZeros(rowSet);
                 rowSet &= ~Integer.lowestOneBit(rowSet);
 
                 //Emit the quad, dont need to clear the data since it not existing in the bitmask is implicit no data
@@ -105,11 +87,120 @@ public class ScanMesher2D {
         }
     }
 
-    protected void emitQuad(int length, int width, long data) {
-        System.err.println("Quad, length: " + length + " width:  " + width + " data: " + data );
+    public final void endPush() {
+        putNext(0);
+        this.currentIndex--;//HACK
+        this.emitRanged(-1);
     }
 
+    protected abstract void emitQuad(int length, int width, long data);
+
     public static void main(String[] args) {
+        var r = new Random(0);
+        long[] data = new long[32*32];
+        float DENSITY = 0.5f;
+        int RANGE = 50;
+        for (int i = 0; i < data.length; i++) {
+            data[i] = r.nextFloat()<DENSITY?(r.nextInt(RANGE)+1):0;
+        }
+
+        int[] qc = new int[2];
+        var mesher = new ScanMesher2D(){
+            @Override
+            protected void emitQuad(int length, int width, long data) {
+                qc[0]++;
+                qc[1]+=length*width;
+            }
+        };
+
+        for (int i = 0; i < 500000; i++) {
+            for (long v : data) {
+                mesher.putNext(v);
+            }
+            mesher.endPush();
+        }
+
+        var m2 = new Mesher2D();
+        for (int i = 0; i < 500000; i++) {
+            int j = 0;
+            m2.reset();
+            for (long v : data) {
+                if (v!=0)
+                    m2.put(j&31, j>>5, v);
+                j++;
+            }
+            m2.process();
+        }
+
+        long t = System.nanoTime();
+        for (int i = 0; i < 1000000; i++) {
+            for (long v : data) {
+                mesher.putNext(v);
+            }
+            mesher.endPush();
+        }
+        long delta = System.nanoTime()-t;
+        System.out.println(delta*1e-6);
+
+
+        t = System.nanoTime();
+        for (int i = 0; i < 1000000; i++) {
+            int j = 0;
+            m2.reset();
+            for (long v : data) {
+                if (v!=0)
+                    m2.put(j&31, j>>5, v);
+                j++;
+            }
+            m2.process();
+        }
+        delta = System.nanoTime()-t;
+        System.out.println(delta*1e-6);
+
+
+    }
+    public static void main3(String[] args) {
+        var r = new Random(0);
+        int[] qc = new int[2];
+        var mesher = new ScanMesher2D(){
+            @Override
+            protected void emitQuad(int length, int width, long data) {
+                qc[0]++;
+                qc[1]+=length*width;
+            }
+        };
+
+        var mesh2 = new Mesher2D();
+
+        float DENSITY = 0.5f;
+        int RANGE = 50;
+        int total = 0;
+        while (true) {
+            DENSITY = r.nextFloat();
+            RANGE = r.nextInt(500)+1;
+            qc[0] = 0; qc[1] = 0;
+            int c = 0;
+            for (int i = 0; i < 32*32; i++) {
+                long val = r.nextFloat()<DENSITY?(r.nextInt(RANGE)+1):0;
+                c += val==0?0:1;
+                mesher.putNext(val);
+                if (val != 0) {
+                    mesh2.put(i&31, i>>5, val);
+                }
+            }
+            mesher.endPush();
+            if (c != qc[1]) {
+                System.out.println(c+", " + qc[1]);
+            }
+            int count = mesh2.process();
+            int delta = count - qc[0];
+            total += delta;
+            System.out.println(total);
+            //System.out.println(c+", new: " + qc[0] + " old: " + count);
+        }
+    }
+
+    public static void main2(String[] args) {
         long[] sample = new long[32*32];
 
         sample[0] = 1;
@@ -130,9 +221,17 @@ public class ScanMesher2D {
         sample[7+32*1] = 2;
         sample[31+32*0] = 6;
         sample[31+32*1] = 6;
+        sample[30+32*2] = 7;
         sample[31+32*2] = 7;
-        sample[31+32*3] = 8;
-        var mesher = new ScanMesher2D();
+        sample[30+32*3] = 7;
+        sample[31+32*3] = 7;
+        sample[31+32*8] = 8;
+        var mesher = new ScanMesher2D() {
+            @Override
+            protected void emitQuad(int length, int width, long data) {
+                System.out.println(length + ", " + width + ", " + data);
+            }
+        };
         int j = 0;
         for (long i : sample) {
             if (j%32 == 0) {