HTML5 Canvas实现图片缩放、翻转、颜色渐变的代码示例

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翻转、移动、平移、放大、缩小

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var canvas = document.getElementById('canvas');
if (canvas.getContext) {
var context = canvas.getContext('2d');
// 放大与缩小
context.beginPath();
context.strokeStyle = "#000000";
context.strokeRect(10,10,150,100);
// 放大3倍
context.scale(3,3);
context.beginPath();
context.strokeStyle = '#cccccc';
context.strokeRect(10,10,150,100)
// 缩小
context.scale(0.5,0.5);
context.beginPath();
context.strokeStyle = '#cccccc';
context.strokeRect(10,10,150,100)
// 翻转
var img = new Image();
img.src = 'images/1.jpg';
img.onload = function(){
context.drawImage(img, 10,10);
context.scale(1, -1);
context.drawImage(img, 0, -500);
}
// 平移
context.beginPath();
context.strokeStyle = '#000000';
context.strokeRect(10,101,150,100);
// x移动 50 y 移动100
context.translate(50,100);
context.beginPath();
context.strokeStyle = '#cccccc';
context.strokeRect(10,10,150,100);
// 旋转
context.beginPath();
context.strokeStyle = '#000000';
context.strokeRect(200,50,100,50);
// 默认旋转是根据0,0中心，使用translate可以按照自己的设置的中心旋转
context.translate(250,75);
context.rotate(45 * Math.PI /180);
context.translate(-250, -75);
context.beginPath();
context.strokeStyle = '#cccccc';
context.strokeRect(200,50,100,50);
// transform 矩阵
context.beginPath();
context.strokeStyle = '#000000';
context.strokeRect(10,10,150,100);
context.transform(3,0,0,3,0,0);
context.beginPath();
context.strokeStyle = '#cccccc';
context.strokeRect(10,10,150,100);
}

渐变、图像组合效果、颜色翻转

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var canvas = document.getElementById('canvas');
if (canvas.getContext) {
var context = canvas.getContext('2d');
// 线性绘制渐变
var grd = context.createLinearGradient(0,0,200,100);
// postion 必须是0.1-1.0之间的竖直，表示渐变中颜色的地点相对地位，color表示颜色
grd.addColorStop(0.1, "#00ff00");
grd.addColorStop(0.8, "#ff0000");
context.fillStyle = grd;
context.fillRect(0,0, 200,100);
// 径向渐变
var grd = context.createRadialGradient(100,100,10,100,100,50);
grd.addColorStop(0.1, "#00ff00");
grd.addColorStop(0.8, '#ff0000');
context.fillStyle = grd;
context.fillRect(0,0,200,200);
// 图像组合效果
context.fillStyle = '#00ff00';
context.fillRect(10,10,50,50);
// 新绘图
//context.globalCompositeOperation = "source-over";
// 只绘制新内容，删除其他所有内容
context.globalCompositeOperation = 'copy';
// 图形重叠的地方，其颜色值相减后决定
context.globalCompositeOperation = 'darker';
// 画布上已经有的内容只会载和其他图形重叠的地方保留
context.globalCompositeOperation = 'destination-atop';
// 参考 http://www.w3school.com.cn/htmldom/prop_canvasrenderingcontext2d_globalcompositeoperation.asp
context.beginPath();
context.fillStyle = '#ff0000';
context.arc(50,50,30,0, 2 * Math.PI);
context.fill();
// 颜色翻转
var img = new Image();
img.src = 'images/1.jpg';
img.onload = function(){
context.drawImage(img, 0,0, 1, 1);
var imgData = context.getImageData(0,0, 1,1);
var pixels = imgData.data;
console.log(pixels);
for(var i = 0, n = pixels.length; i < n; i+=4) {
pixels[i] = 255 - pixels[i];
pixels[i+1] = 255 - pixels[i + 1];
pixels[i+2] = 255 - pixels[i + 2];
}
context.putImageData(imgData, 250, 0);
}
}