canvas小画板——（3）笔锋效果
2024-08-30 05:04:53
画线准备
准备一个canvas
<canvas id="canvasId" width="1000" height="800"></canvas>
使用pointer事件监听，落笔，拖拽，收笔。
document.onpointerdown = function (e) {
if (e.type == "touchstart")
handwriting.down(e.touches[0].pageX, e.touches[0].pageY);
else
handwriting.down(e.x, e.y);
}
document.onpointermove = function (e) {
if (e.type == "touchmove")
handwriting.move(e.touches[0].pageX, e.touches[0].pageY);
else
handwriting.move(e.x, e.y);
}
document.onpointerup = function (e) {
if (e.type == "touchend")
handwriting.up(e.touches[0].pageX, e.touches[0].pageY);
else
handwriting.up(e.x, e.y);
}
主要的逻辑在Handwritinglff 上，存储了当前绘制中的线条的所有点集合，所有绘制过的线条集合pointLines 。
class Handwritinglff {
constructor(canvas) {
this.canvas = canvas;
this.ctx = canvas.getContext("2d")
this.line = new Line();
this.pointLines = new Array();//Line数组
this.k = 0.5;
this.begin = null;
this.middle = null;
this.end = null;
this.lineWidth = 10;
this.isDown = false;
}
down事件的时候初始化当前绘制线条line；
move事件的时候将点加入到当前线条line，并开始绘制
up的时候将点加入绘制线条，并绘制完整一条线。
需要注意的点：
加入点的时候，距离太近的点不需要重复添加；
怎么形成笔锋效果呢
很简单！就是在一条线段的最后几个点的lineWidth不断减小，我们这里选用了最后6个点，如果只选用六个阶梯变化，效果是很难看的，会看到一节节明显的线条变细的过程，如下图：
所以我们有个关键的补点过程，我们会再每6个像素之间补一个点，根据线条粗细变化的范围和最后计算出来的点数，就可以知道每两点连线lineWidth的粗细。
这里的补点过程我们用到了在贝塞尔曲线上补点的算法。具体不明白的可以留言哈
bezierCalculate(poss, precision) {
//维度，坐标轴数（二维坐标，三维坐标...）
let dimersion = 2;
//贝塞尔曲线控制点数（阶数）
let number = poss.length;
//控制点数不小于 2 ，至少为二维坐标系
if (number < 2 || dimersion < 2)
return null;
let result = new Array();
//计算杨辉三角
let mi = new Array();
mi[0] = mi[1] = 1;
for (let i = 3; i <= number; i++) {
let t = new Array();
for (let j = 0; j < i - 1; j++) {
t[j] = mi[j];
}
mi[0] = mi[i - 1] = 1;
for (let j = 0; j < i - 2; j++) {
mi[j + 1] = t[j] + t[j + 1];
}
}
//计算坐标点
for (let i = 0; i < precision; i++) {
let t = i / precision;
let p = new Point(0, 0);
result.push(p);
for (let j = 0; j < dimersion; j++) {
let temp = 0.0;
for (let k = 0; k < number; k++) {
temp += Math.pow(1 - t, number - k - 1) * (j == 0 ? poss[k].x : poss[k].y) * Math.pow(t, k) * mi[k];
}
j == 0 ? p.x = temp : p.y = temp;
}
p.x = this.toDecimal(p.x);
p.y = this.toDecimal(p.y);
}
return result;
}
部分代码如下；
addPoint(p) {
if (this.line.points.length >= 1) {
let last_point = this.line.points[this.line.points.length - 1]
let distance = this.z_distance(p, last_point);
if (distance < 10) {
return;
}
}
if (this.line.points.length == 0) {
this.begin = p;
p.isControl = true;
this.pushPoint(p);
} else {
this.middle = p;
let controlPs = this.computeControlPoints(this.k, this.begin, this.middle, null);
this.pushPoint(controlPs.first);
this.pushPoint(p);
p.isControl = true;
this.begin = this.middle;
}
}
addPoint
draw(isUp = false) {
this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
this.ctx.strokeStyle = "rgba(255,20,87,1)";
//绘制不包含this.line的线条
this.pointLines.forEach((line, index) => {
let points = line.points;
this.ctx.beginPath();
this.ctx.ellipse(points[0].x - 1.5, points[0].y, 6, 3, Math.PI / 4, 0, Math.PI * 2);
this.ctx.fill();
this.ctx.beginPath();
this.ctx.moveTo(points[0].x, points[0].y);
let lastW = line.lineWidth;
this.ctx.lineWidth = line.lineWidth;
this.ctx.lineJoin = "round";
this.ctx.lineCap = "round";
let minLineW = line.lineWidth / 4;
let isChangeW = false;
let changeWidthCount = line.changeWidthCount;
for (let i = 1; i <= points.length; i++) {
if (i == points.length) {
this.ctx.stroke();
break;
}
if (i > points.length - changeWidthCount) {
if (!isChangeW) {
this.ctx.stroke();//将之前的线条不变的path绘制完
isChangeW = true;
if (i > 1 && points[i - 1].isControl)
continue;
}
let w = (lastW - minLineW) / changeWidthCount * (points.length - i) + minLineW;
points[i - 1].lineWidth = w;
this.ctx.beginPath();//为了开启新的路径 否则每次stroke 都会把之前的路径在描一遍
// this.ctx.strokeStyle = "rgba("+Math.random()*255+","+Math.random()*255+","+Math.random()*255+",1)";
this.ctx.lineWidth = w;
this.ctx.moveTo(points[i - 1].x, points[i - 1].y);//移动到之前的点
this.ctx.lineTo(points[i].x, points[i].y);
this.ctx.stroke();//将之前的线条不变的path绘制完
} else {
if (points[i].isControl && points[i + 1]) {
this.ctx.quadraticCurveTo(points[i].x, points[i].y, points[i + 1].x, points[i + 1].y);
} else if (i >= 1 && points[i - 1].isControl) {//上一个是控制点 当前点已经被绘制
} else
this.ctx.lineTo(points[i].x, points[i].y);
}
}
})
//绘制this.line线条
let points;
if (isUp)
points = this.line.points;
else
points = this.line.points.clone();
//当前绘制的线条最后几个补点 贝塞尔方式增加点
let count = 0;
let insertCount = 0;
let i = points.length - 1;
let endPoint = points[i];
let controlPoint;
let startPoint;
while (i >= 0) {
if (points[i].isControl == true) {
controlPoint = points[i];
count++;
} else {
startPoint = points[i];
}
if (startPoint && controlPoint && endPoint) {//使用贝塞尔计算补点
let dis = this.z_distance(startPoint, controlPoint) + this.z_distance(controlPoint, endPoint);
let insertPoints = this.BezierCalculate([startPoint, controlPoint, endPoint], Math.floor(dis / 6) + 1);
insertPoints.splice(0, 1);
insertCount += insertPoints.length;
var index = i;//插入位置
// 把arr2 变成一个适合splice的数组（包含splice前2个参数的数组）
insertPoints.unshift(index, 1);
Array.prototype.splice.apply(points, insertPoints);
//补完点后
endPoint = startPoint;
startPoint = null;
}
if (count >= 6)
break;
i--;
}
//确定最后线宽变化的点数
let changeWidthCount = count + insertCount;
if (isUp)
this.line.changeWidthCount = changeWidthCount;
//制造椭圆头
this.ctx.fillStyle = "rgba(255,20,87,1)"
this.ctx.beginPath();
this.ctx.ellipse(points[0].x - 1.5, points[0].y, 6, 3, Math.PI / 4, 0, Math.PI * 2);
this.ctx.fill();
this.ctx.beginPath();
this.ctx.moveTo(points[0].x, points[0].y);
let lastW = this.line.lineWidth;
this.ctx.lineWidth = this.line.lineWidth;
this.ctx.lineJoin = "round";
this.ctx.lineCap = "round";
let minLineW = this.line.lineWidth / 4;
let isChangeW = false;
for (let i = 1; i <= points.length; i++) {
if (i == points.length) {
this.ctx.stroke();
break;
}
//最后的一些点线宽变细
if (i > points.length - changeWidthCount) {
if (!isChangeW) {
this.ctx.stroke();//将之前的线条不变的path绘制完
isChangeW = true;
if (i > 1 && points[i - 1].isControl)
continue;
}
//计算线宽
let w = (lastW - minLineW) / changeWidthCount * (points.length - i) + minLineW;
points[i - 1].lineWidth = w;
this.ctx.beginPath();//为了开启新的路径 否则每次stroke 都会把之前的路径在描一遍
// this.ctx.strokeStyle = "rgba(" + Math.random() * 255 + "," + Math.random() * 255 + "," + Math.random() * 255 + ",0.5)";
this.ctx.lineWidth = w;
this.ctx.moveTo(points[i - 1].x, points[i - 1].y);//移动到之前的点
this.ctx.lineTo(points[i].x, points[i].y);
this.ctx.stroke();//将之前的线条不变的path绘制完
} else {
if (points[i].isControl && points[i + 1]) {
this.ctx.quadraticCurveTo(points[i].x, points[i].y, points[i + 1].x, points[i + 1].y);
} else if (i >= 1 && points[i - 1].isControl) {//上一个是控制点 当前点已经被绘制
} else
this.ctx.lineTo(points[i].x, points[i].y);
}
}
}
draw
最终效果
动手试试：拖拽写字即可
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