我试图将globalCompositeOperation和JSFiddle结合起来，试图将我的头围绕Codepen属性。
前者使用destination-out，后者使用source-over。是否可以在Codepen中使用火热的光标，还可以删除用户点击的叠加填充部分，如小提琴？
非常感谢任何帮助。我可以将Codepen上的演示结合起来，以便在必要时使用相同的方法。
相关的小提琴代码：
function drawDot(mouseX,mouseY){
bridgeCanvas.beginPath();
bridgeCanvas.arc(mouseX, mouseY, brushRadius, 0, 2*Math.PI, true);
bridgeCanvas.fillStyle = '#000';
bridgeCanvas.globalCompositeOperation = "destination-out";
bridgeCanvas.fill();
}
相关的Codepen代码：
Fire.prototype.clearCanvas = function(){
this.ctx.globalCompositeOperation = "source-over";
this.ctx.fillStyle = "rgba( 15, 5, 2, 1 )";
this.ctx.fillRect( 0, 0, window.innerWidth, window.innerHeight );
this.ctx.globalCompositeOperation = "lighter";
this.ctx.rect(0, 0, this.canvas.width, this.canvas.height);
this.ctx.fillStyle = this.pattern;
this.ctx.fill();/**/
}
答案 0 :(得分：2)
正如我在评论中所说，你必须将你的代码分成至少两部分
裁剪器函数使用"destination-out"合成操作来移除画布中已绘制的像素，其中应绘制新的像素。在您的版本中，它使用背景图像，一旦移除了前景像素，您就可以在画布的现在透明区域中看到此背景。
另一只手中的火焰，使用“较轻”，"color-dodge"和"soft-light"混合操作。这将添加已存在和新绘制像素的颜色
如果在透明区域上使用，则至少第一个将与默认的"source-over"复合操作相同。因此，您需要在画布上绘制背景图像，以便能够在混合中使用它。
为此，您必须使用第二个离屏画布，您只应用橡皮擦 "destination-out"操作。然后，在可见画布上，在每个新的橡皮擦框架中，您必须在可见画布上绘制背景图像，然后使用孔绘制橡皮擦最后是混合一个，它将混合在一起。
这是一个快速代码转储，我在其中重写了一点橡皮擦，并修改了Fire一个，以使我们的主函数处理事件和动画循环。
function MainDrawing(){
this.canvas = document.getElementById('main');
this.ctx = this.canvas.getContext('2d');
this.background = new Image();
this.background.src = "https://s3-us-west-2.amazonaws.com/s.cdpn.io/4273/calgary-bridge-1943.jpg"
this.eraser = new Eraser(this.canvas);
this.fire = new Fire(this.canvas);
this.attachEvents();
}
MainDrawing.prototype = {
anim: function(){
if(this.stopped)
return;
this.ctx.globalCompositeOperation = 'source-over';
this.ctx.drawImage(this.background, 0,0);
this.ctx.drawImage(this.eraser.canvas, 0,0);
this.fire.run();
requestAnimationFrame(this.anim.bind(this));
},
stop: function(){
this.stopped = true;
},
attachEvents: function(){
var mouseDown = false;
this.canvas.onmousedown = function(){
mouseDown = true;
};
this.canvas.onmouseup = function(){
mouseDown = false;
};
this.canvas.onmousemove = function(e){
if(mouseDown){
this.eraser.handleClick(e);
}
this.fire.updateMouse(e);
}.bind(this);
}
};
function Eraser(canvas){
this.main = canvas;
this.canvas = canvas.cloneNode();
var ctx = this.ctx = this.canvas.getContext('2d');
this.img = new Image();
this.img.onload = function(){
ctx.drawImage(this, 0, 0);
ctx.globalCompositeOperation = 'destination-out';
};
this.img.src = "https://s3-us-west-2.amazonaws.com/s.cdpn.io/4273/calgary-bridge-2013.jpg";
this.getRect();
}
Eraser.prototype = {
getRect: function(){
this.rect = this.main.getBoundingClientRect();
},
handleClick: function(evt){
var x = evt.clientX - this.rect.left;
var y = evt.clientY - this.rect.top;
this.draw(x,y);
},
draw: function(x, y){
this.ctx.beginPath();
this.ctx.arc(x, y, 30, 0, Math.PI*2);
this.ctx.fill();
}
};
var Fire = function(canvas){
this.canvas = canvas;
this.ctx = this.canvas.getContext('2d');
this.aFires = [];
this.aSpark = [];
this.aSpark2 = [];
this.mouse = {
x : this.canvas.width * .5,
y : this.canvas.height * .75,
}
}
Fire.prototype.run = function(){
this.update();
this.draw();
}
Fire.prototype.start = function(){
this.bRuning = true;
this.run();
}
Fire.prototype.stop = function(){
this.bRuning = false;
}
Fire.prototype.update = function(){
this.aFires.push( new Flame( this.mouse ) );
this.aSpark.push( new Spark( this.mouse ) );
this.aSpark2.push( new Spark( this.mouse ) );
for (var i = this.aFires.length - 1; i >= 0; i--) {
if( this.aFires[i].alive )
this.aFires[i].update();
else
this.aFires.splice( i, 1 );
}
for (var i = this.aSpark.length - 1; i >= 0; i--) {
if( this.aSpark[i].alive )
this.aSpark[i].update();
else
this.aSpark.splice( i, 1 );
}
for (var i = this.aSpark2.length - 1; i >= 0; i--) {
if( this.aSpark2[i].alive )
this.aSpark2[i].update();
else
this.aSpark2.splice( i, 1 );
}
}
Fire.prototype.draw = function(){
this.drawHalo();
this.ctx.globalCompositeOperation = "overlay";//or lighter or soft-light
for (var i = this.aFires.length - 1; i >= 0; i--) {
this.aFires[i].draw( this.ctx );
}
this.ctx.globalCompositeOperation = "soft-light";//"soft-light";//"color-dodge";
for (var i = this.aSpark.length - 1; i >= 0; i--) {
if( ( i % 2 ) === 0 )
this.aSpark[i].draw( this.ctx );
}
this.ctx.globalCompositeOperation = "color-dodge";//"soft-light";//"color-dodge";
for (var i = this.aSpark2.length - 1; i >= 0; i--) {
this.aSpark2[i].draw( this.ctx );
}
}
Fire.prototype.updateMouse = function( e ){
this.mouse.x = e.clientX;
this.mouse.y = e.clientY;
}
Fire.prototype.drawHalo = function(){
var r = rand( 300, 350 );
this.ctx.globalCompositeOperation = "lighter";
this.grd = this.ctx.createRadialGradient( this.mouse.x, this.mouse.y,r,this.mouse.x, this.mouse.y, 0 );
this.grd.addColorStop(0,"transparent");
this.grd.addColorStop(1,"rgb( 50, 2, 0 )");
this.ctx.beginPath();
this.ctx.arc( this.mouse.x, this.mouse.y - 100, r, 0, 2*Math.PI );
this.ctx.fillStyle= this.grd;
this.ctx.fill();
}
var Flame = function( mouse ){
this.cx = mouse.x;
this.cy = mouse.y;
this.x = rand( this.cx - 25, this.cx + 25);
this.y = rand( this.cy - 5, this.cy + 5);
this.lx = this.x;
this.ly = this.y;
this.vy = rand( 1, 3 );
this.vx = rand( -1, 1 );
this.r = rand( 30, 40 );
this.life = rand( 2, 7 );
this.alive = true;
this.c = {
h : Math.floor( rand( 2, 40) ),
s : 100,
l : rand( 80, 100 ),
a : 0,
ta : rand( 0.8, 0.9 )
}
}
Flame.prototype.update = function()
{
this.lx = this.x;
this.ly = this.y;
this.y -= this.vy;
this.vy += 0.08;
this.x += this.vx;
if( this.x < this.cx )
this.vx += 0.2;
else
this.vx -= 0.2;
if( this.r > 0 )
this.r -= 0.3;
if( this.r <= 0 )
this.r = 0;
this.life -= 0.12;
if( this.life <= 0 ){
this.c.a -= 0.05;
if( this.c.a <= 0 )
this.alive = false;
}else if( this.life > 0 && this.c.a < this.c.ta ){
this.c.a += .08;
}
}
Flame.prototype.draw = function( ctx ){
this.grd1 = ctx.createRadialGradient( this.x, this.y, this.r*3, this.x, this.y, 0 );
this.grd1.addColorStop( 0.5, "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a/20) + ")" );
this.grd1.addColorStop( 0, "transparent" );
this.grd2 = ctx.createRadialGradient( this.x, this.y, this.r, this.x, this.y, 0 );
this.grd2.addColorStop( 0.5, "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")" );
this.grd2.addColorStop( 0, "transparent" );
ctx.beginPath();
ctx.arc( this.x, this.y, this.r * 3, 0, 2*Math.PI );
ctx.fillStyle = this.grd1;
//ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a/20) + ")";
ctx.fill();
ctx.globalCompositeOperation = "overlay";
ctx.beginPath();
ctx.arc( this.x, this.y, this.r, 0, 2*Math.PI );
ctx.fillStyle = this.grd2;
ctx.fill();
ctx.beginPath();
ctx.moveTo( this.lx , this.ly);
ctx.lineTo( this.x, this.y);
ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, 1)";
ctx.lineWidth = rand( 1, 2 );
ctx.stroke();
ctx.closePath();
}
var Spark = function( mouse ){
this.cx = mouse.x;
this.cy = mouse.y;
this.x = rand( this.cx -40, this.cx + 40);
this.y = rand( this.cy, this.cy + 5);
this.lx = this.x;
this.ly = this.y;
this.vy = rand( 1, 3 );
this.vx = rand( -4, 4 );
this.r = rand( 0, 1 );
this.life = rand( 4, 8 );
this.alive = true;
this.c = {
h : Math.floor( rand( 2, 40) ),
s : 100,
l : rand( 40, 100 ),
a : rand( 0.8, 0.9 )
}
}
Spark.prototype.update = function()
{
this.lx = this.x;
this.ly = this.y;
this.y -= this.vy;
this.x += this.vx;
if( this.x < this.cx )
this.vx += 0.2;
else
this.vx -= 0.2;
this.vy += 0.08;
this.life -= 0.1;
if( this.life <= 0 ){
this.c.a -= 0.05;
if( this.c.a <= 0 )
this.alive = false;
}
}
Spark.prototype.draw = function( ctx ){
ctx.beginPath();
ctx.moveTo( this.lx , this.ly);
ctx.lineTo( this.x, this.y);
ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a / 2) + ")";
ctx.lineWidth = this.r * 2;
ctx.lineCap = 'round';
ctx.stroke();
ctx.closePath();
ctx.beginPath();
ctx.moveTo( this.lx , this.ly);
ctx.lineTo( this.x, this.y);
ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
ctx.lineWidth = this.r;
ctx.stroke();
ctx.closePath();
}
rand = function( min, max ){ return Math.random() * ( max - min) + min; };
var app = new MainDrawing();
app.anim();<canvas id="main" width="750" height="465"></canvas>