In the previous article, we introduced the basic knowledge about Canvas and used Canvas to draw various graphics and pictures. Based on the previous article, we will make a tank battle game based on HTML5. Let’s get started.
1. Use Canvas to draw our tank
The tank structure we designed is as shown in the picture below. If some friends have better designs, I hope to share and communicate with them.
As shown in the picture above, our tank is basically composed of three rectangles, a circle and a line segment. The size of each component is marked in px , let’s use the knowledge mentioned in the previous article to draw our tank. Note: When we draw the tank, we should choose a reference point. Here we choose the upper left corner of the tank, as shown in the picture.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
</head>
<body>
<h1>html5-坦克大战</h1>
<!--坦克大战的战场-->
<canvas id="tankMap" width="400px" height="300px" style="background-color:black"></canvas>
<script type="text/javascript">
//得到画布
var canvas1 = document.getElementById("tankMap");
//定义一个位置变量
var heroX = 80;
var heroY = 80;
//得到绘图上下文
var cxt = canvas1.getContext("2d");
//设置颜色
cxt.fillStyle="#BA9658";
//左边的矩形
cxt.fillRect(heroX,heroY,5,30);
//右边的矩形
cxt.fillRect(heroX+17,heroY,5,30);
//画中间的矩形
cxt.fillRect(heroX+6,heroY+5,10,20);
//画出坦克的盖子
cxt.fillStyle="#FEF26E";
cxt.arc(heroX+11,heroY+15,5,0,360,true);
cxt.fill();
//画出炮筒
cxt.strokeStyle="#FEF26E";
cxt.lineWidth=1.5;
cxt.beginPath();
cxt.moveTo(heroX+11,heroY+15);
cxt.lineTo(heroX+11,heroY);
cxt.closePath();
cxt.stroke();
</script>
</body>
</html>
2. How to make the tank move?
Before studying how to make the tank move, let’s first study how to make a small ball move through keyboard operation.
First we add a listening function to the
tag<body onkeydown="test()">
Listening function
//现在按键盘上ASDW移动小球
//说明：当我们按下一个键，实际上触发了一个onkeydown事件
function test(){
var code = event.keyCode; //键盘上字幕的ASCII码
switch(code){
case 87:
ballY--;
break;
case 68:
ballX++;
break;
case 83:
ballY++;
break;
case 65:
ballX--;
break;
}
//重新绘制
drawBall();
}We can define two global variables externally to represent the x-axis and y respectively. The coordinates of the axis, and then change the position of the ball by changing the values of ballX and ballY. We use the WDSA key of the keyboard to control it. The effect is very strange, as shown below:
We did not erase the ball at the previous position when drawing. We should erase it before each redrawing. Post all the codes below:
<body onkeydown="test()">小球上下左右移动
3. Let’s The tank moves
If our tank only moves in one direction, it will be very easy. Just change the drawing of a ball in the above code to drawing of a tank. Before moving the tank, the first thing we should consider is how to make the tank rotate in all directions around its center. Okay, let’s post the above picture and analyze it.
I won’t go into details about the detailed calculation process. I believe everyone is good at mathematics. Calculate the coordinates and positions of each component according to the proportions of the above picture. After the tank is rotated The drawing method is as follows:
//设置颜色
cxt.fillStyle="#BA9658";
//上边的矩形
cxt.fillRect(tank.x-4,tank.y+4,30,5);
//下边的矩形
cxt.fillRect(tank.x-4,tank.y+17+4,30,5);
//画中间的矩形
cxt.fillRect(tank.x+5-4,tank.y+6+4,20,10);
//画出坦克的盖子
cxt.fillStyle="#FEF26E";
cxt.arc(tank.x+15-4,tank.y+11+4,5,0,360,true);
cxt.fill();
//画出炮筒
cxt.strokeStyle="#FEF26E";
cxt.lineWidth=1.5;
cxt.beginPath();
cxt.moveTo(tank.x+15-4,tank.y+11+4);
if(tank.direct==1){ //只是炮筒的方向不同
cxt.lineTo(tank.x+30-4,tank.y+11+4);
}else{
cxt.lineTo(tank.x-4,tank.y+11+4);
}
cxt.closePath();
cxt.stroke();Okay now we find that only the direction of the gun barrel is different when the tank is facing to the left and right. Similarly, only the direction of the gun barrel is different when facing up and down. At this time we can divide the four Each direction is divided into two situations, and then we deal with each small situation. At the same time, the code is encapsulated with OO ideas. The code is as follows:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
</head>
<body onkeydown="getCommand();">
<h1>html5-坦克大战</h1>
<!--坦克大战的战场-->
<canvas id="tankMap" width="400px" height="300px" style="background-color:black"></canvas>
<script type="text/javascript">
//定义一个Hero类(后面还要改进）
//x表示坦克的横坐标
//y表示纵坐标
//direct表示方向
function Hero(x,y,direct){
this.x=x;
this.y=y;
this.speed=1;
this.direct=direct;
//上移
this.moveUp=function(){
this.y-=this.speed;
this.direct=0;
}
//右移
this.moveRight=function(){
this.x+=this.speed;
this.direct=1;
}
//下移
this.moveDown=function(){
this.y+=this.speed;
this.direct=2;
}
//左移
this.moveLeft=function(){
this.x-=this.speed;
this.direct=3;
}
}
//得到画布
var canvas1 = document.getElementById("tankMap");
//得到绘图上下文
var cxt = canvas1.getContext("2d");
//我的tank
//规定0向上、1向右、2向下、3向左
var hero = new Hero(40,40,0);
drawTank(hero);
//绘制坦克
function drawTank(tank){
//考虑方向
switch(tank.direct){
case 0: //向上
case 2: //向下
//设置颜色
cxt.fillStyle="#BA9658";
//左边的矩形
cxt.fillRect(tank.x,tank.y,5,30);
//右边的矩形
cxt.fillRect(tank.x+17,tank.y,5,30);
//画中间的矩形
cxt.fillRect(tank.x+6,tank.y+5,10,20);
//画出坦克的盖子
cxt.fillStyle="#FEF26E";
cxt.arc(tank.x+11,tank.y+15,5,0,360,true);
cxt.fill();
//画出炮筒
cxt.strokeStyle="#FEF26E";
cxt.lineWidth=1.5;
cxt.beginPath();
cxt.moveTo(tank.x+11,tank.y+15);
if(tank.direct==0){ //只是炮筒的方向不同
cxt.lineTo(tank.x+11,tank.y);
}else{
cxt.lineTo(tank.x+11,tank.y+30);
}
cxt.closePath();
cxt.stroke();
break;
case 1:
case 3:
//设置颜色
cxt.fillStyle="#BA9658";
//上边的矩形
cxt.fillRect(tank.x-4,tank.y+4,30,5);
//下边的矩形
cxt.fillRect(tank.x-4,tank.y+17+4,30,5);
//画中间的矩形
cxt.fillRect(tank.x+5-4,tank.y+6+4,20,10);
//画出坦克的盖子
cxt.fillStyle="#FEF26E";
cxt.arc(tank.x+15-4,tank.y+11+4,5,0,360,true);
cxt.fill();
//画出炮筒
cxt.strokeStyle="#FEF26E";
cxt.lineWidth=1.5;
cxt.beginPath();
cxt.moveTo(tank.x+15-4,tank.y+11+4);
if(tank.direct==1){ //只是炮筒的方向不同
cxt.lineTo(tank.x+30-4,tank.y+11+4);
}else{
cxt.lineTo(tank.x-4,tank.y+11+4);
}
cxt.closePath();
cxt.stroke();
break;
}
}
//接收用户按键的函数
function getCommand(){
var code = event.keyCode; //键盘上字幕的ASCII码
switch(code){
case 87:
hero.moveUp();
break;
case 68:
hero.moveRight();
break;
case 83:
hero.moveDown();
break;
case 65:
hero.moveLeft();
break;
}
//把画布清理
cxt.clearRect(0,0,400,300);
//重新绘制
drawTank(hero);
}
</script>
</body>
</html>
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