Javascript画布:旋转玩家时与不完全工作的敌人发生碰撞

简化了磁盘和圆弧之间的碰撞检测问题http://jsfiddle.net/crl/2rz296tf/31（编辑：带@markE建议http://jsfiddle.net/crl/2rz296tf/32/)（用于调试：http://jsfiddle.net/crl/2rz296tf/27/)

比较角度的一些实用函数：

function mod(x, value){ // Euclidean modulo http://jsfiddle.net/cLvmrs6m/4/
    return x>=0 ? x%value : value+ x%value;
}
function angularize(x){
    return mod(x+pi, 2*pi)-pi;
}

碰撞检测：

var d_enemy_player = dist(enemy.pos, player.pos)
if (d_enemy_player>player.shieldradius-enemy.radius && d_enemy_player<player.shieldradius+enemy.radius){ 
    //only worth checking when we are approaching the shield distance
    var angle_enemy = atan2(enemy.pos.y-player.pos.y, enemy.pos.x-player.pos.x)
    var delta_with_leftofshield = angularize(angle_enemy-player.angle-player.shieldwidth)
    var delta_with_rightofshield = angularize(angle_enemy-player.angle+player.shieldwidth)
    var delta_with_shield = angularize(angle_enemy-player.angle)
    if (delta_with_leftofshield<0 && delta_with_rightofshield>0){
        console.log('boom')
        enemy.destroyed = true;
    } else if(delta_with_shield>=0 ){
        // check distance with right extremety of shield's arc
        console.log('right')
        var d_rightofshield_enemy = dist(enemy.pos, {x:player.pos.x+player.shieldradius*cos(player.angle+player.shieldwidth), y:player.pos.y+player.shieldradius*sin(player.angle+player.shieldwidth)});
        if (d_rightofshield_enemy<enemy.radius){
            console.log('right boom')
            enemy.destroyed = true;
        }
    } else {
        console.log('left')
        var d_leftofshield_enemy = dist(enemy.pos, {x:player.pos.x+player.shieldradius*cos(player.angle-player.shieldwidth), y:player.pos.y+player.shieldradius*sin(player.angle-player.shieldwidth)});
        if (d_leftofshield_enemy<enemy.radius){
            console.log('left boom')
            enemy.destroyed = true;
        }
    }
}

Html5画布有一个非常好的命中测试方法：context.isPointInPath

你可以用这个方法来测试一个圆是否与你的盾牌碰撞。它可以在屏蔽的所有角度工作。

在您的情况下，路径将是半径为player.shield.radius-enemy.radius的内弧和半径为player.shield.radius+enemy.radius的外弧。

在mousemove内，只需绘制（不划）盾牌路径的2条弧线，并使用context.isPointInside( enemy.centerX, enemy.centerY )测试每个敌人的中心点。

为了获得更好的精度，将盾牌路径的扫掠范围扩大到两端敌人的半径。

以下是示例代码和演示：

function log() {
  console.log.apply(console, arguments);
}
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var cw = canvas.width;
var ch = canvas.height;
function reOffset() {
  var BB = canvas.getBoundingClientRect();
  offsetX = BB.left;
  offsetY = BB.top;
}
var offsetX, offsetY;
reOffset();
window.onscroll = function(e) {
  reOffset();
}
window.onresize = function(e) {
  reOffset();
}
var isDown = false;
var startX, startY;
var cx = cw / 2;
var cy = ch / 2;
var radius = 100;
var startAngle = Math.PI/6;
var enemyRadius = 15;
var shieldStrokeWidth = 8;
var endRadians = enemyRadius / (2 * Math.PI * radius) * (Math.PI * 2);
defineShieldHitPath(cx, cy, radius, enemyRadius, startAngle);
drawShield(cx, cy, radius, startAngle, shieldStrokeWidth);
$("#canvas").mousemove(function(e) {
  handleMouseMove(e);
});
function defineShieldHitPath(cx, cy, r, enemyRadius, startAngle) {
  ctx.beginPath();
  ctx.arc(cx, cy, r - enemyRadius - shieldStrokeWidth / 2, startAngle - endRadians, startAngle + Math.PI + endRadians);
  ctx.arc(cx, cy, r + enemyRadius + shieldStrokeWidth / 2, startAngle + Math.PI + endRadians, startAngle - endRadians, true);
  ctx.closePath();
  ctx.lineWidth = 1;
  ctx.strokeStyle = 'black';
  // stroked just for the demo.
  // you don't have to stroke() if all you're doing is 'isPointInPath'
  ctx.stroke();
}
function drawShield(cx, cy, r, startAngle, strokeWidth) {
  ctx.beginPath();
  ctx.arc(cx, cy, r, startAngle, startAngle + Math.PI);
  ctx.lineWidth = strokeWidth;
  ctx.strokeStyle = 'blue';
  ctx.stroke();
}
function drawEnemy(cx, cy, r, fill) {
  ctx.beginPath();
  ctx.arc(cx, cy, r, 0, Math.PI * 2);
  ctx.fillStyle = fill;
  ctx.fill();
}
function handleMouseMove(e) {
  // tell the browser we're handling this event
  e.preventDefault();
  e.stopPropagation();
  mouseX = parseInt(e.clientX - offsetX);
  mouseY = parseInt(e.clientY - offsetY);
  ctx.clearRect(0, 0, cw, ch);
  drawShield(cx, cy, radius, startAngle, shieldStrokeWidth);
  defineShieldHitPath(cx, cy, radius, enemyRadius, startAngle);
  if (ctx.isPointInPath(mouseX, mouseY)) {
    drawEnemy(mouseX, mouseY, enemyRadius, 'red');
  } else {
    drawEnemy(mouseX, mouseY, enemyRadius, 'green');
  }
}

body{ background-color: ivory; }
#canvas{border:1px solid red; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>The shield is the blue arc.<br>The filled circle that moves with the mouse is the enemy.<br>The black stroked arc is the shield perimiter.<br>The enemy turns red when colliding with the blue shield.<br>Test by moving the mouse-enemy in / out of the shield perimiter.</h4>
<canvas id="canvas" width=400 height=400></canvas>

为了获得最佳性能，您也可以在数学上进行相同的isPointInPath命中测试。

这是一个由两部分组成的测试。测试#1：敌人的中心点是否在盾牌的扫掠角内（使用数学atan2）。测试#2：敌人的圆心是否在盾牌路径弧的内半径和外半径之间。如果这两个测试都是真的，那么敌人正在与盾牌路径碰撞。

代码的问题似乎是比较角度的方式。别忘了2Pi和0是完全一样的。看看这个例子：你有两个角度，a和b。

a=0.1*Pi

b=1.9*Pi

a略高于x轴，而b略低于x轴。

从两者来看，a似乎都领先于b，所以你会认为a>b是真的。但是等一下！看看这些数字，b比a大得多！当你想检查一个角度是否在一个区间之间时，你必须确保你的区间是连续的，在这种情况下，当角度=0时，这是错误的。

这是我的解决方案。我尽我所能测试了它，但你永远不会知道你是否错过了什么。

// Gets the equivalent angle between 0 and MAX
var normalize_angle = function( angle )
{
    var MAX = Math.PI * 2;  // Value for a full rotation. Should be 360 in degrees
    angle %= MAX;
    return angle < 0 ? angle + MAX : angle;
};
var is_angle_between = function( alpha, min, max )
{
    // Convert all the angles to be on the same rotation, between 0 and MAX
    alpha = normalize_angle( alpha );
    min = normalize_angle( min );
    max = normalize_angle( max );
    if( max > min )
    {   // Check if the equal case fits your needs. It's a bit pointless for floats
        return max >= alpha && min <= alpha;    // Traditional method works
    } else {    // This happens when max goes beyond MAX, so it starts from 0 again
        return max >= alpha || min <= alpha;    // alpha has to be between max and 0 or
                                                //                 between min and MAX
    }
};

要使用它，请将您的防护功能更改为：

shield: 
    function (player, spawn) {
        return (this.distance(player, spawn) <= player.radius + spawn.radius) && 
            is_angle_between(this.tangent(player, spawn), angle , angle - Math.PI );
    }
}