Matrix Rotate

MatrixRotate Illustration

The MatrixRotate operation rotates the coordinate system by rotate degrees relative to a pivot point (pivotX, pivotY).

<div id="matrixRotateContainer"> <canvas id="matrixRotateCanvas_v1" width="500" height="330" style="border:1px solid #ccc; background: #fff; display: block; margin: 10px 0;"></canvas> </div> <script> (function() { var angle = 0; function draw() { var canvas = document.getElementById('matrixRotateCanvas_v1'); if (!canvas) { setTimeout(draw, 100); return; } var ctx = canvas.getContext('2d'); if (!ctx) return; var BLUE = '#0047AB', GRAY = '#888888', DARK_GRAY = '#444444', BLUE_TRANS = 'rgba(0, 71, 171, 0.2)'; ctx.clearRect(0, 0, 500, 330); var px = 250, py = 165; angle = (angle + 1) % 360; function drawHouse(ctx, x, y, w, h, color, alpha) { ctx.save(); ctx.globalAlpha = alpha || 1.0; ctx.translate(x, y); // Body ctx.fillStyle = color; ctx.fillRect(0, -h * 0.6, w, h * 0.6); // Roof ctx.beginPath(); ctx.moveTo(0, -h * 0.6); ctx.lineTo(w / 2, -h); ctx.lineTo(w, -h * 0.6); ctx.closePath(); ctx.fill(); // Door ctx.fillStyle = 'white'; ctx.fillRect(w * 0.35, -h * 0.25, w * 0.3, h * 0.25); ctx.restore(); } // Original ctx.strokeStyle = '#eee'; ctx.lineWidth = 1; ctx.setLineDash([4, 4]); ctx.strokeRect(px, py - 80, 80, 80); ctx.setLineDash([]); drawHouse(ctx, px, py, 80, 80, '#ddd', 0.5); ctx.font = '16px Arial'; ctx.fillStyle = '#bbb'; ctx.fillText('Original', px + 8, py - 90); // Rotated ctx.save(); ctx.translate(px, py); ctx.rotate(angle * Math.PI / 180); drawHouse(ctx, 0, 0, 80, 80, BLUE, 0.6); ctx.lineWidth = 2; ctx.strokeStyle = BLUE; ctx.strokeRect(0, -80, 80, 80); ctx.restore(); // Pivot Anchor ctx.beginPath(); ctx.arc(px, py, 7, 0, 2 * Math.PI); ctx.fillStyle = DARK_GRAY; ctx.fill(); // Labels ctx.font = 'bold 20px Arial'; ctx.fillStyle = DARK_GRAY; ctx.fillText('Pivot (px, py)', px + 15, py + 25); ctx.font = 'bold 24px Arial'; ctx.fillText('rotate: ' + angle + '°', 35, 50); requestAnimationFrame(draw); } draw(); })(); </script>