Question

我正在使用HTML的画布和JavaScript开发类似小行星的街机游戏。我目前有一堆随机生成的形状（“小行星”），随机数点（3,4或5）和随机位置的随机大小。

我正在尝试使用这些多边形设置碰撞检测系统。我一直在使用SAT.js（https://github.com/jriecken/sat-js）。但是，我无法准确地在屏幕上呈现的实际多边形周围绘制不可见的碰撞多边形。

这是我在小行星类中所拥有的，我在渲染小行星。我目前只测试形状（三角形）中的3个点。我关掉了4点和5点的小行星。

ctx.moveTo(0, 0);
ctx.lineTo(10 + size, 20); 
ctx.lineTo(10 + size, 20 + size);  
ctx.closePath();

这是相应的SAT.js代码。

/**
  * @function createCollisionPolygon
  * Traces the outline of the asteroid to allow it to detect collisions
  * based on the number of points the shape has (3, 4, or 5)
  * @param {asteroid} The asteroid to make collision detectable
  * @return The traced polygon
  */
function createCollisionPolygon(asteroid)
{
  var V = SAT.Vector;
  var P = SAT.Polygon;
  var polygon;
  switch(asteroid.randomNumPoints)
  {
    // 3 point polygon
    case 3:
      polygon = new P(new V(asteroid.position.x, asteroid.position.y), [
      new V(10 + asteroid.size, 0),
      new V(asteroid.position.x,asteroid.position.y),
      new V(10 + asteroid.size, 20 + asteroid.size)
      ]);
      break;
  }
  return polygon;
}

/**
  * @function checkCollision
  * Checks for collisions between any two asteroids
  * @param {polygon1} The first asteroid  
  * @param {polygon2} The next asteroid
  * @return True if there was a collision, false otherwise
  */
function checkCollision(polygon1, polygon2)
{
  var response = new SAT.Response();
  var collided = SAT.testPolygonPolygon(polygon1, polygon2, response);
  return collided;
}

稍后会在这里调用：

 
  for(var i = 0; i < asteroids.length - 1; i++)
  {
    var asteroid1 = asteroids[i];
    var asteroid2 = asteroids[i+1];

    // Trace an invisible outline around each asteroid
    var polygon1 = createCollisionPolygon(asteroid1); 
    var polygon2 = createCollisionPolygon(asteroid2);

    // console.log("Polygon 1: "+ console.log(polygon1.points[0]
    //  + console.log(polygon1.points[1]) + console.log(polygon1.points[2])));
    // console.log("Polygon 2: " + console.log(polygon2.points[0]
    //  + console.log(polygon2.points[1]) + console.log(polygon2.points[2])));

    // Check if there is a collision
    if(checkCollision(polygon1, polygon2))
    {
      asteroid1.color = 'red';
      asteroid2.color = 'red';
      console.log("Collision detected.");
    }
  }

任何帮助都会受到赞赏 - 我一直在努力解决这个问题。谢谢！

Answer 1

因为没有用于检索交叉区域的画布剪辑属性。我会建议下一个解决方案。使用js库之一进行poligon交集计算，例如Greiner-Hormann。使用此lib，您可以轻松地与形状相交并检测碰撞（如果交叉结果不为null，则存在碰撞）。

示例：

var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');

function drawTriangle(trianglePoints, color)
{
  ctx.beginPath();
  ctx.moveTo(trianglePoints[0].x, trianglePoints[0].y);
  ctx.lineTo(trianglePoints[1].x, trianglePoints[1].y); 
  ctx.lineTo(trianglePoints[2].x, trianglePoints[2].y);  
  ctx.closePath();
  ctx.fillStyle = color;
  ctx.fill();
 }

function getTriangle(size, startPointX, startPointY)
{
  return [{x:startPointX,y:startPointY},
          {x:startPointX + size,y:startPointY},
          {x:startPointX,y:startPointY + size},
          {x:startPointX,y:startPointY}];
}

//sample triangles
var triangle1 = getTriangle(50,100,100);
var triangle2 = getTriangle(50,100,90);
var triangle3 = getTriangle(50,200,100);
var triangle4 = getTriangle(50,280,90);

//draw all triangles
drawTriangle(triangle1,'#d3d3d3');
drawTriangle(triangle2,'#e3e3e3');
drawTriangle(triangle3,'red');
drawTriangle(triangle4,'blue');

//intersaction results
console.log("intersection exists");
console.log(greinerHormann.intersection( triangle1 , triangle2));
console.log("intersection not exists result of intersaction - null");
console.log(greinerHormann.intersection( triangle3 , triangle2));

<script src="https://cdn.rawgit.com/w8r/GreinerHormann/master/dist/greiner-hormann.min.js"></script>
<canvas id="myCanvas" width="578" height="200"></canvas>

JavaScript多边形碰撞检测

1 个答案: