开发第一个Html5游戏（二）
今天我们继续学习Html5系列游戏开发，我们会在第一章的基础上做一些扩展，加入颜色渐变、
绘制文本、自定义文本样式、以及动画，我们还将学习UI中一个非常重要的元素，按钮。
我们的上一篇文章: （译）开发第一个Html5游戏（一）
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JS代码：（完整代码请看文章结尾链接）
var canvas, ctx;
var circles = [];
var selectedCircle;
var hoveredCircle;
var button;
var moving = false;
var speed = 2.0;
// -------------------------
// objects :
function Circle(x, y, radius){
this.x = x;
this.y = y;
this.radius = radius;
}
function Button(x, y, w, h, state, image) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.state = state;
this.imageShift = 0;
this.image = image;
}
// -------------------------
// draw functions :
function clear() { // clear canvas function
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
function drawCircle(ctx, x, y, radius) { // draw circle function
ctx.fillStyle = 'rgba(255, 35, 55, 1.0)';
ctx.beginPath();
ctx.arc(x, y, radius, 0, Math.PI*2, true);
ctx.closePath();
ctx.fill();
ctx.lineWidth = 1;
ctx.strokeStyle = 'rgba(0, 0, 0, 1.0)';
ctx.stroke(); // draw border
}
function drawScene() { // main drawScene function
clear(); // clear canvas
// 绘制文本
ctx.font = '42px DS-Digital';
ctx.textAlign = 'center';
ctx.fillStyle = '#ffffff';
ctx.fillText('Welcome to lesson #2', ctx.canvas.width/2, 50);
//这里实现颜色渐变
var bg_gradient = ctx.createLinearGradient(0, 200, 0, 400);
bg_gradient.addColorStop(0.0, 'rgba(255, 0, 0, 0.8)');
bg_gradient.addColorStop(0.5, 'rgba(0, 255, 0, 0.8)');
bg_gradient.addColorStop(1.0, 'rgba(0, 0, 255, 0.8)');
ctx.beginPath(); // custom shape begin
ctx.fillStyle = bg_gradient;
ctx.moveTo(circles[0].x, circles[0].y);
for (var i=0; i<circles.length; i++) {
ctx.lineTo(circles[i].x, circles[i].y);
}
ctx.closePath(); // custom shape end
ctx.fill(); // fill custom shape
ctx.lineWidth = 2;
ctx.strokeStyle = 'rgba(0, 0, 255, 0.5)';
ctx.stroke(); // draw border
// reverting direction
if (circles[0].x <= 300 || circles[0].x >= 385) {
speed = -speed;
}
// 实现图像抖动
if (moving) {
circles[0].x -= speed;
circles[0].y -= speed;
circles[1].x += speed;
circles[1].y -= speed;
circles[2].x += speed;
circles[2].y += speed;
circles[3].x -= speed;
circles[3].y += speed;
}
drawCircle(ctx, circles[0].x, circles[0].y, (hoveredCircle == 0) ? 25 : 15);
drawCircle(ctx, circles[1].x, circles[1].y, (hoveredCircle == 1) ? 25 : 15);
drawCircle(ctx, circles[2].x, circles[2].y, (hoveredCircle == 2) ? 25 : 15);
drawCircle(ctx, circles[3].x, circles[3].y, (hoveredCircle == 3) ? 25 : 15);
// draw button
ctx.drawImage(button.image, 0, button.imageShift, button.w, button.h, button.x, button.y, button.w, button.h);
// draw text
ctx.font = '30px DS-Digital';
ctx.fillStyle = '#ffffff';
ctx.fillText('Play/Pause', 135, 480);
ctx.fillText(button.state, 135, 515);
}
// -------------------------
// initialization
$(function(){
canvas = document.getElementById('scene');
ctx = canvas.getContext('2d');
var circleRadius = 15;
var width = canvas.width;
var height = canvas.height;
// lets add 4 circles manually
circles.push(new Circle(width / 2 - 20, height / 2 - 20, circleRadius));
circles.push(new Circle(width / 2 + 20, height / 2 - 20, circleRadius));
circles.push(new Circle(width / 2 + 20, height / 2 + 20, circleRadius));
circles.push(new Circle(width / 2 - 20, height / 2 + 20, circleRadius));
// 图片按钮
buttonImage = new Image();
buttonImage.src = 'images/button.png';
buttonImage.onload = function() {
}
button = new Button(50, 450, 180, 120, 'normal', buttonImage);
// binding mousedown event (for dragging)
$('#scene').mousedown(function(e) {
var mouseX = e.layerX || 0;
var mouseY = e.layerY || 0;
for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
var circleX = circles[i].x;
var circleY = circles[i].y;
var radius = circles[i].radius;
if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
selectedCircle = i;
break;
}
}
// button behavior
if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
button.state = 'pressed';
button.imageShift = 262;
}
});
$('#scene').mousemove(function(e) { // binding mousemove event for dragging selected circle
var mouseX = e.layerX || 0;
var mouseY = e.layerY || 0;
if (selectedCircle != undefined) {
// var canvasPosition = $(this).offset();
var radius = circles[selectedCircle].radius;
circles[selectedCircle] = new Circle(mouseX, mouseY,radius); // changing position of selected circle
}
hoveredCircle = undefined;
for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
var circleX = circles[i].x;
var circleY = circles[i].y;
var radius = circles[i].radius;
if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
hoveredCircle = i;
circles[hoveredCircle] = new Circle(circleX, circleY, 25);
break;
}
}
// button behavior
if (button.state != 'pressed') {
button.state = 'normal';
button.imageShift = 0;
if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
button.state = 'hover';
button.imageShift = 131;
}
}
});
$('#scene').mouseup(function(e) { // on mouseup - cleaning selectedCircle
selectedCircle = undefined;
// button behavior
if (button.state == 'pressed') {
moving = !moving;
}
button.state = 'normal';
button.imageShift = 0;
});
setInterval(drawScene, 30); // loop drawScene
});