HTML5画布和javascript烟花特效

学会做一个烟花HTML5画布和JavaScript。在这个演示,像素大小的火箭发射自动从底部的屏幕,通过鼠标的点击。您还可以单击并拖动来启动多个焰火。　　　　本教程介绍了跟踪和对象包含在数组循环,跟踪鼠标点击和坐标,动画烟花特定目标坐标,使美丽的粒子爆炸通过使用随机生成的值HTMLCanvas is not supported in your browser.CSS/* basic styles for black background and crosshair cursor */body { background: #000; margin: 0;}canvas { cursor: crosshair; display: block;}JS// when animating on canvas, it is best to use requestAnimationFrame instead of setTimeout or setInterval// not supported in all browsers though and sometimes needs a prefix, so we need a shimwindow.requestAnimFrame = ( function() { return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function( callback ) { window.setTimeout( callback, 1000 / 60 ); };})();// now we will setup our basic variables for the demovar canvas = document.getElementById( 'canvas' ), ctx = canvas.getContext( '2d' ), // full screen dimensions cw = window.innerWidth, ch = window.innerHeight, // firework collection fireworks = [], // particle collection particles = [], // starting hue hue = 120, // when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks limiterTotal = 5, limiterTick = 0, // this will time the auto launches of fireworks, one launch per 80 loop ticks timerTotal = 80, timerTick = 0, mousedown = false, // mouse x coordinate, mx, // mouse y coordinate my; // set canvas dimensionscanvas.width = cw;canvas.height = ch;// now we are going to setup our function placeholders for the entire demo// get a random number within a rangefunction random( min, max ) { return Math.random() * ( max - min ) + min;}// calculate the distance between two pointsfunction calculateDistance( p1x, p1y, p2x, p2y ) { var xDistance = p1x - p2x, yDistance = p1y - p2y; return Math.sqrt( Math.pow( xDistance, 2 ) + Math.pow( yDistance, 2 ) );}// fireworkfunction Firework( sx, sy, tx, ty ) { // actual coordinates this.x = sx; this.y = sy; // starting coordinates this.sx = sx; this.sy = sy; // target coordinates this.tx = tx; this.ty = ty; // distance from starting point to target this.distanceToTarget = calculateDistance( sx, sy, tx, ty ); this.distanceTraveled = 0; // track the past coordinates of each firework to a trail effect, increase the coordinate count to more prominent trails this.coordinates = []; this.coordinateCount = 3; // populate initial coordinate collection with the current coordinates while( this.coordinateCount-- ) { this.coordinates.push( [ this.x, this.y ] ); } this.angle = Math.atan2( ty - sy, tx - sx ); this.speed = 2; this.acceleration = 1.05; this.brightness = random( 50, 70 ); // circle target indicator radius this.targetRadius = 1;}// update fireworkFirework.prototype.update = function( index ) { // remove last item in coordinates array this.coordinates.pop(); // add current coordinates to the start of the array this.coordinates.unshift( [ this.x, this.y ] ); // cycle the circle target indicator radius if( this.targetRadius < 8 ) { this.targetRadius += 0.3; } else { this.targetRadius = 1; } // speed up the firework this.speed *= this.acceleration; // get the current velocities based on angle and speed var vx = Math.cos( this.angle ) * this.speed, vy = Math.sin( this.angle ) * this.speed; // how far will the firework have traveled with velocities applied? this.distanceTraveled = calculateDistance( this.sx, this.sy, this.x + vx, this.y + vy ); // if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached if( this.distanceTraveled >= this.distanceToTarget ) { Particles( this.tx, this.ty ); // remove the firework, use the index passed into the update function to determine which to remove fireworks.splice( index, 1 ); } else { // target not reached, keep traveling this.x += vx; this.y += vy; }}// draw fireworkFirework.prototype.draw = function() { ctx.beginPath(); // move to the last tracked coordinate in the set, then draw a line to the current x and y ctx.moveTo( this.coordinates[ this.coordinates.length - 1][ 0 ], this.coordinates[ this.coordinates.length - 1][ 1 ] ); ctx.lineTo( this.x, this.y ); ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)'; ctx.stroke(); ctx.beginPath(); // draw the target for this firework with a pulsing circle ctx.arc( this.tx, this.ty, this.targetRadius, 0, Math.PI * 2 ); ctx.stroke();}// particlefunction Particle( x, y ) { this.x = x; this.y = y; // track the past coordinates of each particle to a trail effect, increase the coordinate count to more prominent trails this.coordinates = []; this.coordinateCount = 5; while( this.coordinateCount-- ) { this.coordinates.push( [ this.x, this.y ] ); } // set a random angle in all possible directions, in radians this.angle = random( 0, Math.PI * 2 ); this.speed = random( 1, 10 ); // friction will slow the particle down this.friction = 0.95; // gravity will be applied and pull the particle down this.gravity = 1; // set the hue to a random number +-20 of the overall hue variable this.hue = random( hue - 20, hue + 20 ); this.brightness = random( 50, 80 ); this.alpha = 1; // set how fast the particle fades out this.decay = random( 0.015, 0.03 );}// update particleParticle.prototype.update = function( index ) { // remove last item in coordinates array this.coordinates.pop(); // add current coordinates to the start of the array this.coordinates.unshift( [ this.x, this.y ] ); // slow down the particle this.speed *= this.friction; // apply velocity this.x += Math.cos( this.angle ) * this.speed; this.y += Math.sin( this.angle ) * this.speed + this.gravity; // fade out the particle this.alpha -= this.decay; // remove the particle once the alpha is low enough, based on the passed in index if( this.alpha <= this.decay ) { particles.splice( index, 1 ); }}// draw particleParticle.prototype.draw = function() { ctx. beginPath(); // move to the last tracked coordinates in the set, then draw a line to the current x and y ctx.moveTo( this.coordinates[ this.coordinates.length - 1 ][ 0 ], this.coordinates[ this.coordinates.length - 1 ][ 1 ] ); ctx.lineTo( this.x, this.y ); ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')'; ctx.stroke();}// particle group/explosionfunction Particles( x, y ) { // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though var particleCount = 30; while( particleCount-- ) { particles.push( new Particle( x, y ) ); }}// main demo loopfunction loop() { // this function will run endlessly with requestAnimationFrame requestAnimFrame( loop ); // increase the hue to get different colored fireworks over time hue += 0.5; // normally, clearRect() would be used to clear the canvas // we want to a trailing effect though // setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely ctx.globalCompositeOperation = 'destination-out'; // decrease the alpha property to more prominent trails ctx.fillStyle = 'rgba(0, 0, 0, 0.5)'; ctx.fillRect( 0, 0, cw, ch ); // change the composite operation back to our main mode // lighter s bright highlight points as the fireworks and particles overlap each other ctx.globalCompositeOperation = 'lighter'; // loop over each firework, draw it, update it var i = fireworks.length; while( i-- ) { fireworks[ i ].draw(); fireworks[ i ].update( i ); } // loop over each particle, draw it, update it var i = particles.length; while( i-- ) { particles[ i ].draw(); particles[ i ].update( i ); } // launch fireworks automatically to random coordinates, when the mouse isn't down if( timerTick >= timerTotal ) { if( !mousedown ) { // start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen fireworks.push( new Firework( cw / 2, ch, random( 0, cw ), random( 0, ch / 2 ) ) ); timerTick = 0; } } else { timerTick++; } // limit the rate at which fireworks get launched when mouse is down if( limiterTick >= limiterTotal ) { if( mousedown ) { // start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target fireworks.push( new Firework( cw / 2, ch, mx, my ) ); limiterTick = 0; } } else { limiterTick++; }}// mouse event bindings// update the mouse coordinates on mousemovecanvas.addEventListener( 'mousemove', function( e ) { mx = e.pageX - canvas.offsetLeft; my = e.pageY - canvas.offsetTop;});// toggle mousedown state and prevent canvas from being selectedcanvas.addEventListener( 'mousedown', function( e ) { e.preventDefault(); mousedown = true;});canvas.addEventListener( 'mouseup', function( e ) { e.preventDefault(); mousedown = false;});// once the window loads, we are ready for some fireworks!window.onload = loop;

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