HTML5 Canvas如何实现图片缩放、翻转、颜色渐变的代码示例

发布时间：2022-12-31 13:51:15 来源：互联网

.

现实情况远非想的那么单纯容易清晰：当优越感逐渐转为失落感甚至挫败感时，当由坚信自己是一块金子到怀疑自己是一粒沙子时，愤怒，迷茫，自卑，焦急，躁动就开始与日俱增。

翻转、移动、平移、放大、缩小

XML/HTML Code复制内容到剪贴板

varcanvas=document.getElementById('canvas');
if(canvas.getContext){
varcontext=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
varimg=newImage();
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50y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

XML/HTML Code复制内容到剪贴板

varcanvas=document.getElementById('canvas');
if(canvas.getContext){
varcontext=canvas.getContext('2d');
//线性绘制渐变
vargrd=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
vargrd=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
varimg=newImage();
img.src='images/1.jpg';
img.onload=function(){
context.drawImage(img,0,0,1,1);
varimgData=context.getImageData(0,0,1,1);
varpixels=imgData.data;
console.log(pixels);
for(vari=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);
}
}