我得到了这个我正在努力的HTML5画布项目。 基本上我试图在点击时添加新粒子。 并且粒子被推到粒子阵列，但是 粒子没有显示出来。我可以看到粒子被鼠标坐标推到了数组中，但它看起来并不像最后一个粒子被绘制出来。 我做错了什么？
参见示例。
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set full-screen
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// Options
var num = 100; // Number of particles to draw
var size = 2; // Particle size
var color = '#dd64e6'; // Particle color
var min_speed = .3; // Particle min speed
var max_speed = 2; // Particle max speed
var dist = 100; // Max distance before line gets cut
var dist_sq = dist * dist; // Dist squared
var line_width = 2; // Line width
var background = '#181b23'; // Background color
var line_color = '#1d2631'; // Line color
var fps = 60;
var now, delta;
var then = Date.now();
var interval = 1000 / fps;
if (/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)) {
num = 10;
fps = 29;
}
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle(false, false)
);
}
// Lets animate the particle
function draw() {
// Loop
requestAnimationFrame(draw);
now = Date.now();
delta = now - then;
if (delta > interval) {
then = now - (delta % interval);
// Background
ctx.fillStyle = background;
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
draw_particles();
}
}
// Draw particles
function draw_particles() {
for (var t = 0; t < num; t++) {
// This particle
var p = particles[t];
for (var q = t + 1; q < num; q++) {
// Check X first, maybe we don't need to
// calculate Y
var x = particles[q].x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = particles[q].y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, particles[q].x, particles[q].y);
}
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
}
// Return a particle object
function create_particle(xPos, yPos) {
// Position
if (xPos == false && yPos == false) {
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
} else {
this.x = xPos;
this.y = yPos;
}
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Size
this.radius = size;
console.log('particle created at: ' + this.x + ', ' + this.y);
}
// Returns an random integer, positive or negative
// between the given value
function random_int_between(min, max) {
var num = Math.floor(Math.random() * max) - min;
num *= Math.floor(Math.random() * 2) == 1 ? 1 : -1;
return num;
}
// Draw a line between 2 particles
// given the particles x and y position
function draw_line(p_x, p_y, p2_x, p2_y) {
ctx.beginPath();
ctx.lineWidth = line_width;
ctx.strokeStyle = line_color;
ctx.moveTo(p_x, p_y);
ctx.lineTo(p2_x, p2_y);
ctx.stroke();
}
// When the canvas is clicked
// add new particle
function clicked(e) {
var mouseXpos, mouseYpos;
if (e.offsetX) {
mouseXpos = e.offsetX;
mouseYpos = e.offsetY;
} else if (e.layerX) {
mouseXpos = e.layerX;
mouseYpos = e.layerY;
}
particles.push(
new create_particle(mouseXpos, mouseYpos)
);
}
canvas.addEventListener('click', function(e) {
clicked(e);
}, false);
draw();<!DOCTYPE html>
<html>
<head>
<style>
* {margin:0;padding:0;overflow:hidden;}
</style>
</head>
<body>
<canvas id="canvas">{{-- The background --}}</canvas>
</body>
</html>
答案 0 :(得分：1)
好吧，除了评论中没有其他人回答这个问题，我想我会回答这个问题，以便其他人可能不会想到同样的事情。
问题是您使用变量“num”来保存粒子数。如果你改为使用“particles.length”，你可以
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set full-screen
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// Options
var num = 100; // Number of particles to draw
var size = 2; // Particle size
var color = '#dd64e6'; // Particle color
var min_speed = .3; // Particle min speed
var max_speed = 2; // Particle max speed
var dist = 100; // Max distance before line gets cut
var dist_sq = dist * dist; // Dist squared
var line_width = 2; // Line width
var background = '#181b23'; // Background color
var line_color = '#1d2631'; // Line color
var fps = 60;
var now, delta;
var then = Date.now();
var interval = 1000 / fps;
if (/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)) {
num = 10;
fps = 29;
}
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle(false, false)
);
}
// Lets animate the particle
function draw() {
// Loop
requestAnimationFrame(draw);
now = Date.now();
delta = now - then;
if (delta > interval) {
then = now - (delta % interval);
// Background
ctx.fillStyle = background;
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
draw_particles();
}
}
// Draw particles
function draw_particles() {
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = t + 1; q < particles.length; q++) {
// Check X first, maybe we don't need to
// calculate Y
var x = particles[q].x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = particles[q].y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, particles[q].x, particles[q].y);
}
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
}
// Return a particle object
function create_particle(xPos, yPos) {
// Position
if (xPos == false && yPos == false) {
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
} else {
this.x = xPos;
this.y = yPos;
}
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Size
this.radius = size;
console.log('particle created at: ' + this.x + ', ' + this.y);
}
// Returns an random integer, positive or negative
// between the given value
function random_int_between(min, max) {
var num = Math.floor(Math.random() * max) - min;
num *= Math.floor(Math.random() * 2) == 1 ? 1 : -1;
return num;
}
// Draw a line between 2 particles
// given the particles x and y position
function draw_line(p_x, p_y, p2_x, p2_y) {
ctx.beginPath();
ctx.lineWidth = line_width;
ctx.strokeStyle = line_color;
ctx.moveTo(p_x, p_y);
ctx.lineTo(p2_x, p2_y);
ctx.stroke();
}
// When the canvas is clicked
// add new particle
function clicked(e) {
var mouseXpos, mouseYpos;
if (e.offsetX) {
mouseXpos = e.offsetX;
mouseYpos = e.offsetY;
} else if (e.layerX) {
mouseXpos = e.layerX;
mouseYpos = e.layerY;
}
particles.push(
new create_particle(mouseXpos, mouseYpos)
);
}
canvas.addEventListener('click', function(e) {
clicked(e);
}, false);
draw();<!DOCTYPE html>
<html>
<head>
<style>
* {margin:0;padding:0;overflow:hidden;}
</style>
</head>
<body>
<canvas id="canvas">{{-- The background --}}</canvas>
</body>
</html>
我敢于超出我们问题的范围，因为您可以通过利用Array.prototype.forEach来防止此类问题，并移动点的绘制并将它们约束到新函数。具有简化代码的额外好处。
// Draw particles
function draw_particles() {
particles.forEach(function(p,pi){
particles.forEach(function(p2,p2i){
if(pi === p2i){
return;
}
// Check X first, maybe we don't need to
// calculate Y
var x = p2.x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = p2.y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, p2.x, p2.y);
draw_dot(p);
constrain(p);
}
}
});
});
}
// Draw particle
function draw_dot(p){
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
ctx.closePath();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (particles.length === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
}
// Constrain particle movement
function constrain(p){
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
使用Array.prototype.length和Array.prototype.forEach可以降低进入数组索引问题的风险。