From 434fed1cd6092c7c8cc24bc2cbd95d1d4a425494 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Mon, 20 Oct 2025 14:52:11 -0700
Subject: continue work on decoder, support auto tile size

---
 Scripts/DataDecoder.cs | 67 ++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 59 insertions(+), 8 deletions(-)

(limited to 'Scripts/DataDecoder.cs')

diff --git a/Scripts/DataDecoder.cs b/Scripts/DataDecoder.cs
index 810c46a..1128e2f 100644
--- a/Scripts/DataDecoder.cs
+++ b/Scripts/DataDecoder.cs
@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using UdonSharp;
 using UnityEngine;
 using VRC.SDK3.Rendering;
@@ -6,9 +7,12 @@ using VRC.Udon.Common.Interfaces;
 public class DataDecoder : UdonSharpBehaviour
 {
   public RenderTexture sourceTexture;
-  public int tileSize = 8;
   public int tileToCheck = 0;
 
+  private int tileSize = 8;
+  // Minimum size (in pixels) of a tile. This is shared with our tixl operator.
+  private const int kMinTileSize = 4;
+  private const int kMaxTileSize = 128;
   private Color32[] pixelData;
   private bool hasData = false;
   private int readWidth;
@@ -18,9 +22,8 @@ public class DataDecoder : UdonSharpBehaviour
 
   void Update()
   {
-    if (sourceTexture == null || tileSize <= 0) return;
+    if (sourceTexture == null) return;
 
-    // TODO get more than one column
     int requestWidth = Mathf.Min(tileSize, sourceTexture.width);
     int requestHeight = sourceTexture.height;
     int pixelCount = requestWidth * requestHeight;
@@ -62,21 +65,69 @@ public class DataDecoder : UdonSharpBehaviour
 
   private void ProcessTiles()
   {
-    if (pixelData == null || readWidth <= 0 || readHeight <= 0) return;
+    // Get the tile size.
+    {
+      int oldTileSize = tileSize;
+      tileSize = kMinTileSize;
+      tileSize = Parse24BitTile(0);
+      tileSize = Mathf.Clamp(tileSize, kMinTileSize, kMaxTileSize);
+      if (tileSize != oldTileSize) {
+        Debug.Log($"Tile size changed from {oldTileSize} to {tileSize}");
+      }
+    }
+
+    // Get the length. This is in units of subpixels. So we will need to access
+    // ceil(length/3) tiles.
+    int lengthSubpixels = Parse24BitTile(1);
+    int lengthTiles = (int) Mathf.Ceil(lengthSubpixels/3.0f);
+
+    // Collect all nibbles into a flat array. Note that these are still
+    // encoded.
+    var nibbles = new List<int>(lengthSubpixels);
+    for (int tile_i = 0; tile_i < lengthTiles; tile_i++) {
+      GetTileRGB(tile_i+2, out int r, out int g, out int b);
+      nibbles.Add(r);
+      if (nibbles.Count < nibbles.Capacity) {
+        nibbles.Add(g);
+      }
+      if (nibbles.Count < nibbles.Capacity) {
+        nibbles.Add(b);
+      }
+    }
+
+    // Convert nibbles to bytes.
+    var bytes = nibbles;
+    for (int i = 0; i < nibbles.Count/2; i++) {
+      // See DataEncoder.cs. It puts the upper 4 bits before the lower 4 bits.
+      bytes[i] = (nibbles[2*i] & 0xF0) | ((nibbles[2*i+1] & 0xF0) >> 4);
+    }
+    // Remove second half of list.
+    bytes.RemoveRange(nibbles.Count/2, nibbles.Count/2);
 
     int tilesPerColumn = (int) Mathf.Floor(readHeight / tileSize);
+  }
+
+  private int Parse24BitTile(int tileIdx)
+  {
+    GetTileRGB(tileIdx, out int r, out int g, out int b);
+    int data = 0;
+    data |= DecodeNibble(r);
+    data |= DecodeNibble(g) << 4;
+    data |= DecodeNibble(b) << 8;
+    return data;
+  }
 
-    GetTileRGB(tileToCheck, out int r, out int g, out int b);
-    Debug.Log($"Tile {tileToCheck}: R={r}, G={g}, B={b}");
+  private int DecodeNibble(int subpixel) {
+    return (subpixel >> 4) & 0x0F;
   }
 
-  private void GetTileRGB(int tileIndex, out int r, out int g, out int b)
+  private void GetTileRGB(int tileIdx, out int r, out int g, out int b)
   {
     r = 0;
     g = 0;
     b = 0;
 
-    int tileY = tileIndex * tileSize;
+    int tileY = tileIdx * tileSize;
     int centerY = tileY + tileSize / 2;
 
     if (centerY >= readHeight) return;
-- 
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