HTML5 Canvas实现放大镜效果示例canvas离屏技术与放大镜实现代码示例Canvas实现放大镜效果完整案例分析(附代码)

 var canvas = document.getElementById("canvas"); var context = canvas.getContext("2d"); var img = document.getElementById("img");

 // 图片被放大区域的中心点，也是放大镜的中心点 var centerPoint = {}; // 图片被放大区域的半径 var originalRadius = 100; // 图片被放大区域 var originalRectangle = {}; // 放大倍数 var scale = 2; // 放大后区域 var scaleGlassRectangle

 function drawBackGround() { context.drawImage(img, 0, 0); }

 function calOriginalRectangle(point) { originalRectangle.x = point.x - originalRadius; originalRectangle.y = point.y - originalRadius; originalRectangle.width = originalRadius * 2; originalRectangle.height = originalRadius * 2; }

 context.save(); context.beginPath(); context.arc(centerPoint.x, centerPoint.y, originalRadius, 0, Math.PI * 2, false); context.clip(); ...... context.restore();

 scaleGlassRectangle = { x: centerPoint.x - originalRectangle.width * scale / 2, y: centerPoint.y - originalRectangle.height * scale / 2, width: originalRectangle.width * scale, height: originalRectangle.height * scale }

 context.drawImage(canvas, originalRectangle.x, originalRectangle.y, originalRectangle.width, originalRectangle.height, scaleGlassRectangle.x, scaleGlassRectangle.y, scaleGlassRectangle.width, scaleGlassRectangle.height );

 context.beginPath(); var gradient = context.createRadialGradient( centerPoint.x, centerPoint.y, originalRadius - 5, centerPoint.x, centerPoint.y, originalRadius); gradient.addColorStop(0, 'rgba(0,0,0,0.2)'); gradient.addColorStop(0.80, 'silver'); gradient.addColorStop(0.90, 'silver'); gradient.addColorStop(1.0, 'rgba(150,150,150,0.9)'); context.strokeStyle = gradient; context.lineWidth = 5; context.arc(centerPoint.x, centerPoint.y, originalRadius, 0, Math.PI * 2, false); context.stroke();

 canvas.onmousemove = function (e) { ...... }

 function windowToCanvas(x, y) { var bbox = canvas.getBoundingClientRect(); return {x: x - bbox.left, y: y - bbox.top} }

 #canvas { display: block; border: 1px solid red; margin: 0 auto; cursor: crosshair; }

 function Line(xStart, yStart, xEnd, yEnd, index, color) { // 起点x坐标 this.xStart = xStart; // 起点y坐标 this.yStart = yStart; // 终点x坐标 this.xEnd = xEnd; // 终点y坐标 this.yEnd = yEnd; // 用来标记是哪条线段 this.index = index; // 线段颜色 this.color = color; }

 // 原始线段 var chartLines = new Array(); // 处于放大镜中的原始线段 var glassLines; // 放大后的线段 var scaleGlassLines; // 位于放大镜中的线段数量 var glassLineSize; function initLines() { var line; line = new Line(200.5, 400, 200.5, 200, 0, "#888"); chartLines.push(line); line = new Line(201.5, 400, 201.5, 20, 1, "#888"); chartLines.push(line); glassLineSize = chartLines.length; glassLines = new Array(glassLineSize); for (var i = 0; i < glassLineSize; i++) { line = new Line(0, 0, 0, 0, i); glassLines[i] = line; } scaleGlassLines = new Array(glassLineSize); for (var i = 0; i < glassLineSize; i++) { line = new Line(0, 0, 0, 0, i); scaleGlassLines[i] = line; } }

 function drawLines() { var line; context.lineWidth = 1; for (var i = 0; i < chartLines.length; i++) { line = chartLines[i]; context.beginPath(); context.strokeStyle = line.color; context.moveTo(line.xStart, line.yStart); context.lineTo(line.xEnd, line.yEnd); context.stroke(); } }

 function calGlassRectangle(point) { originalRectangle.x = point.x - originalRadius; originalRectangle.y = point.y - originalRadius; originalRectangle.width = originalRadius * 2; originalRectangle.height = originalRadius * 2; scaleGlassRectangle.width = originalRectangle.width * scale; scaleGlassRectangle.height = originalRectangle.height * scale; scaleGlassRectangle.x = originalRectangle.x + originalRectangle.width / 2 - scaleGlassRectangle.width / 2; scaleGlassRectangle.y = originalRectangle.y + originalRectangle.height / 2 - scaleGlassRectangle.height / 2; // 将值装换为整数 scaleGlassRectangle.width = parseInt(scaleGlassRectangle.width); scaleGlassRectangle.height = parseInt(scaleGlassRectangle.height); scaleGlassRectangle.x = parseInt(scaleGlassRectangle.x); scaleGlassRectangle.y = parseInt(scaleGlassRectangle.y); }

 function calScaleLines() { var xStart = originalRectangle.x; var xEnd = originalRectangle.x + originalRectangle.width; var yStart = originalRectangle.y; var yEnd = originalRectangle.y + originalRectangle.height; var line, gLine, sgLine; var glassLineIndex = 0; for (var i = 0; i < chartLines.length; i++) { line = chartLines[i]; // 判断线段是否在放大镜中 if (line.xStart < xStart || line.xEnd > xEnd) { continue; } if (line.yEnd > yEnd || line.yStart < yStart) { continue; } gLine = glassLines[glassLineIndex]; sgLine = scaleGlassLines[glassLineIndex]; if (line.yEnd > yEnd) { gLine.yEnd = yEnd; } if (line.yStart < yStart) { gLine.yStart = yStart; } gLine.xStart = line.xStart - xStart; gLine.yStart = line.yStart - yStart; gLine.xEnd = line.xEnd - xStart; gLine.yEnd = line.yEnd - yStart; sgLine.xStart = parseInt(gLine.xStart * scale); sgLine.yStart = parseInt(gLine.yStart * scale); sgLine.xEnd = parseInt(gLine.xEnd * scale); sgLine.yEnd = parseInt(gLine.yEnd * scale); sgLine.color = line.color; glassLineIndex++; } glassLineSize = glassLineIndex; }

 function drawAnchor() { context.beginPath(); cont
                
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