From 605e6d04b9243527b3ca78a5a1522426dd085737 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sat, 19 Aug 2023 12:54:28 -0700
Subject: [PATCH] better

---
 index.html | 91 +++++++++++++++++++++++++++---------------------------
 1 file changed, 46 insertions(+), 45 deletions(-)

diff --git a/index.html b/index.html
index c9892e6..e0b8d79 100644
--- a/index.html
+++ b/index.html
@@ -74,11 +74,29 @@
                 return Array.from(block).map((n) => n.toString(16)).join('');
             }
 
-            function inverse(block) {
-                return block.map((n) => ~n & 0xf);
+            function inverse(pixel) {
+                return ~pixel & 0xf;
             }
 
-            function drawChar(bits, cx, cy, char, charset) {
+            function matchBlocks(a, b, threshold) {
+                for (let i = 0; i < blockWidth * blockHeight; i++) {
+                    if (Math.abs(a[i] - b[i]) > threshold) {
+                        return false;
+                    }
+                }
+                return true;
+            }
+
+            function matchBlocksInverse(a, b, threshold) {
+                for (let i = 0; i < blockWidth * blockHeight; i++) {
+                    if (Math.abs(a[i] - inverse(b[i])) > threshold) {
+                        return false;
+                    }
+                }
+                return true;
+            }
+
+            function drawChar(imageData, cx, cy, char, charset) {
                 let invert = Boolean(char & 0x80);
                 char &= 0x7f;
                 if (char >= charset.length) {
@@ -88,16 +106,16 @@
                 for (let y = 0; y < blockHeight; y++) {
                     for (let x = 0; x < blockWidth; x++) {
                         let i = y * blockWidth + x;
-                        let ii = (y + cy * blockHeight) * bits.width + (x + cx * blockWidth);
+                        let ii = (y + cy * blockHeight) * imageData.width + (x + cx * blockWidth);
                         let gray16 = block[i];
                         if (invert) {
-                            gray16 = ~gray16 & 0x0f;
+                            gray16 = inverse(gray16);
                         }
                         let gray256 = Math.round(gray16 * 255 / 15);
-                        bits.data[ii * 4] = gray256;
-                        bits.data[ii * 4 + 1] = gray256;
-                        bits.data[ii * 4 + 2] = gray256;
-                        bits.data[ii * 4 + 3] = 255;
+                        imageData.data[ii * 4] = gray256;
+                        imageData.data[ii * 4 + 1] = gray256;
+                        imageData.data[ii * 4 + 2] = gray256;
+                        imageData.data[ii * 4 + 3] = 255;
                     }
                 }
             }
@@ -146,36 +164,12 @@
                 //
                 // First pass: uniques extraction
                 // Convert the 4bpp pixel indices into hex strings
-                let blockMap = {};
                 let uniques = [];
-                /*
-                for (let i = 0; i < chars.length; i++) {
-                    let char = chars[i];
-                    let block = blocks[char];
-                    let key = hexify(blocks[i]);
-                    let keyInverse = hexify(inverse(block));
-                    if (blockMap[key]) {
-                        char = blockMap[key];
-                    } else if (blockMap[keyInverse]) {
-                        char = blockMap[keyInverse];
-                    } else {
-                        char = uniques.push(block) - 1;
-                        blockMap[key] = char;
-                        blockMap[keyInverse] = char;
-                    }
-                    chars[i] = char;
-                }
-                */
 
                 for (let threshold = 0; threshold < 16; threshold++) {
                     charIter:
-                    for (let i = 0; i < chars.length; i++) {
-                        let char = chars[i];
-                        let block = blocks[char];
-                        if (!block) {
-                            debugger
-                            throw new Error('missing block');
-                        }
+                    for (let i = 0; i < blocks.length; i++) {
+                        let block = blocks[i];
 
                         fontMatch:
                         for (let j = 0; j < uniques.length; j++) {
@@ -184,14 +178,16 @@
                                 debugger
                                 throw new Error('missing other');
                             }
-                            for (let k = 0; k < blockWidth * blockHeight; k++) {
-                                if (Math.abs(block[k] - other[k]) > threshold) {
-                                    continue fontMatch;
-                                }
+                            if (matchBlocks(block, other, threshold)) {
+                                // we're close enough to reuse a character
+                                chars[i] = j;
+                                continue charIter;
+                            } else if (matchBlocksInverse(block, other, threshold)) {
+                                chars[i] = j | 0x8000;
+                                continue charIter;
+                            } else {
+                                continue fontMatch;
                             }
-                            // we're close enough to reuse a character
-                            chars[i] = j;
-                            continue charIter;
                         }
                         // add a new char
                         chars[i] = uniques.push(block) - 1;
@@ -200,13 +196,12 @@
                         break;
                     }
                     // We need to decimate further
-                    blocks = uniques;
                     uniques = [];
                 }
                 let span = document.querySelector('#block-count');
                 span.textContent = `${uniques.length}`;
 
-                // Font (currently wrong! :D)
+                // Font
                 let fontCtx = document.querySelector('#font').getContext('2d');
                 let font = fontCtx.createImageData(16 * blockWidth, 16 * blockHeight);
                 for (let hi = 0; hi < 16; hi++) {
@@ -222,7 +217,13 @@
                 for (let cy = 0; cy < heightBlocks; cy++) {
                     for (let cx = 0; cx < widthBlocks; cx++) {
                         let i = cy * widthBlocks + cx;
-                        drawChar(bits, cx, cy, chars[i], uniques);
+                        let char = chars[i];
+                        if (char & 0x8000) {
+                            // we use a bigger bit during earlier stages
+                            char &= 0x7f;
+                            char |= 0x80;
+                        }
+                        drawChar(bits, cx, cy, char, uniques);
                     }
                 }
                 ctx.putImageData(bits, 0, 0);