Matrix digital rain · gpt-5.4-nano
Create the Matrix digital rain effect on a full-screen black canvas: columns of falling green katakana glyphs with a trailing fade and a brighter leading character.
transcript · 14 messages
Create the Matrix digital rain effect on a full-screen black canvas: columns of falling green katakana glyphs with a trailing fade and a brighter leading character.
thinking
**Creating a canvas effect** I need to create an index.html file that features a canvas matrix effect, and it will all be in one file. I'll use requestAnimationFrame for smooth rendering. Choosing a monospace font and focusing on the katakana Unicode range will be important. Each column will have an array of drops, and I'll draw with globalAlpha for fading effects. To achieve the trailing effect, I'll overlay a semi-transparent black rectangle at a low alpha. The current characters will appear brighter, while the trailing characters will be slightly dimmed. Full-screen and resize handling are also essential!
index.html (3956 bytes)Successfully wrote 3956 bytes to index.html
thinking
**Fixing code issues** I need to make sure the code is correct. It sounds like the extras list mistakenly includes something invalid, "0x30ル." I also noticed that the canvas variable is using fontSize and columnCount without declaring them first, which could lead to them becoming global variables. I'll need to fix these errors. Let’s start by editing the index.html file and read through it to catch any other issues along the way!
{"path":"index.html","offset":1,"limit":220}<!doctype html> <html lang="en"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1" /> <title>Matrix Rain</title> <style> html, body { margin: 0; height: 100%; background: #000; overflow: hidden; font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; } canvas { display: block; width: 100vw; height: 100vh; background: #000; } </style> </head> <body> <canvas id="c"></canvas> <script> (() => { const canvas = document.getElementById('c'); const ctx = canvas.getContext('2d', { alpha: false }); // Crisp text on various DPR settings. let dpr = Math.max(1, window.devicePixelRatio || 1); function resize() { dpr = Math.max(1, window.devicePixelRatio || 1); canvas.width = Math.floor(window.innerWidth * dpr); canvas.height = Math.floor(window.innerHeight * dpr); canvas.style.width = window.innerWidth + 'px'; canvas.style.height = window.innerHeight + 'px'; // Character size based on screen width/height to keep it looking right. // (Using a stable monospace-like size rather than measuring each glyph.) const minDim = Math.min(window.innerWidth, window.innerHeight); fontSize = Math.max(12, Math.floor(minDim / 30)); // feels similar across sizes columnCount = Math.floor(canvas.width / (fontSize * dpr)); // Reset drop positions. drops = new Array(columnCount).fill(0); ctx.imageSmoothingEnabled = false; ctx.textBaseline = 'top'; } let fontSize = 16; let columnCount = 0; let drops = []; // Katakana range-ish: 0x30A0..0x30FF (ァ..ヿ) plus some extensions. const glyphs = (() => { const out = []; for (let cp = 0x30A0; cp <= 0x30FF; cp++) out.push(String.fromCharCode(cp)); // A few extra common katakana/related marks. const extras = [ 0x3041, 0x3042, 0x30FC, 0x30FD, 0x30E1, 0x30E9, 0x30EA, 0x30ル, 0x30EF, 0x30A1, 0x30A5, 0x30A8, 0x30AA ]; for (const cp of extras) out.push(String.fromCharCode(cp)); return out; })(); function randKatakana() { return glyphs[(Math.random() * glyphs.length) | 0]; } // Draw loop function tick() { const w = canvas.width; const h = canvas.height; // Trailing fade: paint a translucent black rectangle. // Lower alpha => longer trails. ctx.fillStyle = 'rgba(0, 0, 0, 0.06)'; ctx.fillRect(0, 0, w, h); ctx.font = `${fontSize}px ui-monospace, Menlo, Consolas, monospace`; for (let i = 0; i < columnCount; i++) { const x = i * fontSize * dpr; const y = drops[i] * fontSize * dpr; // Brighter leading character. // Slightly vary brightness per column. const leadAlpha = 0.95; const leadGreen = 180 + Math.random() * 50; // bright-ish ctx.fillStyle = `rgba(0, ${leadGreen | 0}, 0, ${leadAlpha})`; ctx.fillText(randKatakana(), x, y); // Advance drop. // Most of the time, fall by one row; occasionally skip for variation. if (Math.random() > 0.985) { drops[i] += 2; } else { drops[i] += 1; } // When a column reaches the bottom, reset to the top. if (y > h && Math.random() > 0.5) { drops[i] = 0; } } requestAnimationFrame(tick); } window.addEventListener('resize', resize, { passive: true }); // Initialize. resize(); // Start with a full black background. ctx.fillStyle = '#000'; ctx.fillRect(0, 0, canvas.width, canvas.height); requestAnimationFrame(tick); })(); </script> </body> </html>
thinking
**Fixing bugs in the code** I need to address a bug where the extras array includes an invalid hex and a katakana character, 0x30ル. There's also an issue with font size and columnCount being undefined because they're declared after the resize function. However, I see that resize() is called after the let declarations, which should be okay. The main focus now is to correct the extras list so that it contains the proper values, specifically using cp number like 0x30EB for "ル". Let's edit the file accordingly.**Enhancing visual effects** I want to include a trailing fade effect with a brighter head and dimmer tail. Currently, each frame only paints the head once, while the tail is created by persistently showing rectangles. That’s fine, but maybe I should add some color variation and a gradient trail. Also, I could dim non-leading characters randomly to create some brightness variation. As a final touch, I'll replace the invalid cp 0x30ル with 0x30EB and ensure other necessary extras like 0x3041 and 0x3042 are included. Let's make those edits!
{"path":"index.html","edits":[{"oldText":" 0x3041, 0x3042, 0x30FC, 0x30FD, 0x30E1, 0x30E9, 0x30EA, 0x30ル,","newText":" 0x3Successfully replaced 1 block(s) in index.html.
{"path":"index.html","edits":[{"oldText":" const extras = [\n 0x3041, 0x3042, 0x30FC, 0x30FD, 0x30E1, 0x30E9, 0x30EA, 0x30EBSuccessfully replaced 1 block(s) in index.html.
{"path":"index.html","limit":120}<!doctype html> <html lang="en"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1" /> <title>Matrix Rain</title> <style> html, body { margin: 0; height: 100%; background: #000; overflow: hidden; font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; } canvas { display: block; width: 100vw; height: 100vh; background: #000; } </style> </head> <body> <canvas id="c"></canvas> <script> (() => { const canvas = document.getElementById('c'); const ctx = canvas.getContext('2d', { alpha: false }); // Crisp text on various DPR settings. let dpr = Math.max(1, window.devicePixelRatio || 1); function resize() { dpr = Math.max(1, window.devicePixelRatio || 1); canvas.width = Math.floor(window.innerWidth * dpr); canvas.height = Math.floor(window.innerHeight * dpr); canvas.style.width = window.innerWidth + 'px'; canvas.style.height = window.innerHeight + 'px'; // Character size based on screen width/height to keep it looking right. // (Using a stable monospace-like size rather than measuring each glyph.) const minDim = Math.min(window.innerWidth, window.innerHeight); fontSize = Math.max(12, Math.floor(minDim / 30)); // feels similar across sizes columnCount = Math.floor(canvas.width / (fontSize * dpr)); // Reset drop positions. drops = new Array(columnCount).fill(0); ctx.imageSmoothingEnabled = false; ctx.textBaseline = 'top'; } let fontSize = 16; let columnCount = 0; let drops = []; // Katakana range-ish: 0x30A0..0x30FF (ァ..ヿ) plus some extensions. const glyphs = (() => { const out = []; for (let cp = 0x30A0; cp <= 0x30FF; cp++) out.push(String.fromCharCode(cp)); // A few extra common katakana/related marks. const extras = [ 0x3041, 0x3042, 0x30FC, // long vowel mark 0x30FD, 0x30E1, 0x30E9, 0x30EA, 0x30EB, 0x30EF, 0x30A1, 0x30A5, 0x30A8, 0x30AA ]; for (const cp of extras) out.push(String.fromCharCode(cp)); return out; })(); function randKatakana() { return glyphs[(Math.random() * glyphs.length) | 0]; } // Draw loop function tick() { const w = canvas.width; const h = canvas.height; // Trailing fade: paint a translucent black rectangle. // Lower alpha => longer trails. ctx.fillStyle = 'rgba(0, 0, 0, 0.06)'; ctx.fillRect(0, 0, w, h); ctx.font = `${fontSize}px ui-monospace, Menlo, Consolas, monospace`; for (let i = 0; i < columnCount; i++) { const x = i * fontSize * dpr; const y = drops[i] * fontSize * dpr; // Brighter leading character. // Slightly vary brightness per column. const leadAlpha = 0.95; const leadGreen = 180 + Math.random() * 50; // bright-ish ctx.fillStyle = `rgba(0, ${leadGreen | 0}, 0, ${leadAlpha})`; ctx.fillText(randKatakana(), x, y); // Advance drop. // Most of the time, fall by one row; occasionally skip for variation. if (Math.random() > 0.985) { drops[i] += 2; } else { drops[i] += 1; } // When a column reaches the bottom, reset to the top. if (y > h && Math.random() > 0.5) { drops[i] = 0; } } requestAnimationFrame(tick); } window.addEventListener('resize', resize, { passive: true }); // Initialize. resize(); [11 more lines in file. Use offset=121 to continue.]
{"path":"index.html","offset":121,"limit":80}// Start with a full black background. ctx.fillStyle = '#000'; ctx.fillRect(0, 0, canvas.width, canvas.height); requestAnimationFrame(tick); })(); </script> </body> </html>
Created **`index.html`** with a full-screen **Matrix-style digital rain** on a black canvas (green falling Katakana columns, translucent trailing fade, and a brighter leading character).
TAKE IT TO CODE
A single self-contained HTML file — copy it and open in any browser, or reuse the prompt with your own pi-agent run.
RUN
EVALUATION
Classic Matrix digital rain with green katakana columns, fading trails, and continuous animation; no interactivity but not required.
Vision grade · anthropic/claude-sonnet-5
MEASUREMENTS
Raw readings from the capture, not a verdict — the grade above is the only judgement. Percentages are how much of the screen changed; the measure under-reports sparse motion on a dark background.