Tạo hiệu ứng bắn pháo hoa bằng HTML5 và Javascript

10/01/2014 webmaster

Nhằm mang đến cho các bạn có thêm nhiều kinh nghiệm trong việc sử dụng HTML5 và Javascript . Hôm nay mình xin chia sẻ cho các bạn từng bước làm hiệu ứng bắn pháo hoa đẹp mắt ngay trong trang web của chính các bạn. Qua bài viết này , các bạn có thể hiểu rõ cơ bản cũng như nắm rõ hơn về HTML5 Canvas.

Xem Demo | Download

Bước 1 : HTML
Chúng ta chỉ cần chèn thẻ và dòng thông báo hiển thị cho những trình duyệt chưa hỗ trợ thẻ này.

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Bước 2 : CSS

Chúng ta sẽ chỉ cần định dạng nền đen và chuyển con trỏ chuột về dấu thập ( Cross Hair ) là xong.

1 2 3 4 5 6 7 8 9

body {     background: #000;     margin: 0; }   canvas {     cursor: crosshair;     display: block; }

Bước 3 : Javascript

Đây là phần quan trọng nhất trong bài viết, để tạo hiệu ứng bắn pháo hoa, các bạn copy toàn bộ đoạn script trên để áp dụng cho chính website hay blog của mình.

// 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 shim

window.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 demo

var 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 dimensions

canvas.width = cw;

canvas.height = ch;

 

// now we are going to setup our function placeholders for the entire demo

 

// get a random number within a range

function random( min, max ) {

    return Math.random() * ( max - min ) + min;

}

 

// calculate the distance between two points

function calculateDistance( p1x, p1y, p2x, p2y ) {

    var xDistance = p1x - p2x,

            yDistance = p1y - p2y;

    return Math.sqrt( Math.pow( xDistance, 2 ) + Math.pow( yDistance, 2 ) );

}

 

// create firework

function 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 create a trail effect, increase the coordinate count to create 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 firework

Firework.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 ) {

        createParticles( 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 firework

Firework.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();

}

 

// create particle

function Particle( x, y ) {

    this.x = x;

    this.y = y;

    // track the past coordinates of each particle to create a trail effect, increase the coordinate count to create 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 particle

Particle.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 particle

Particle.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();

}

 

// create particle group/explosion

function createParticles( 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 loop

function 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 create 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 create 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 creates 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 mousemove

canvas.addEventListener( 'mousemove', function( e ) {

    mx = e.pageX - canvas.offsetLeft;

    my = e.pageY - canvas.offsetTop;

});

 

// toggle mousedown state and prevent canvas from being selected

canvas.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;

Trong đoạn script trên, từng phần đều có chú thích hướng dẫn từng bước cụ thể, do đó nếu bạn nào muốn tìm hiểu kỹ hơn thì có thể đọc tham khảo. Có một điều cần lưu ý là để có thể chạy được hiệu ứng bắn pháo hoa, các bạn nhớ đặt toàn bộ đoạn script bên trên nằm ngay trước thẻ đóng

nha các bạn.

Nếu các bạn gặp vướng mắc gì trong lúc hoàn thiện bài viết, hay có câu hỏi gì cần được giải đáp trong bài viết này thì đừng ngần ngại để lại lời nhắn dưới dạng comments sau mỗi bài viết nhé.