检测鼠标是否在画布内的对象上

Question

我在canvas元素中创建了一条线.我正在寻找最简单的方法来检测鼠标的位置是否在画布内部的行内.

我已经使用这个函数来查看画布内鼠标的位置,但我对如何继续操作感到很困惑.

function getMousePos(c, evt) {
            var rect = c.getBoundingClientRect();
            return {
                x: evt.clientX - rect.left,
                y: evt.clientY - rect.top
            };
        }

我也看过这个主题Fabricjs检测鼠标在对象路径上,但它检测鼠标是否在画布内,而不是在对象内.

我创建的行是较小行的一部分,彼此连接.

 for (var i = 0; i < 140 ; i++) {

                ctx.beginPath();

                ctx.moveTo(x[i],y[i]);
                ctx.quadraticCurveTo(x[i],50,x[i+1],y[i+1]);
                ctx.lineWidth = 40;

                ctx.strokeStyle = 'white';
                ctx.lineCap = 'round';
                ctx.stroke();

            }

其中x [i]和y [i]是具有我想要的坐标的数组.

我希望我的问题很清楚,虽然我对javascript不是很熟悉.

谢谢迪米特拉

Answer 1

演示:http: //jsfiddle.net/m1erickson/Cw4ZN/

您需要这些概念来检查鼠标是否在一行内:

• 定义一条线的起点和终点

• 听取鼠标事件

• 在鼠标移动时,检查鼠标是否在该行的指定距离内

这是一个带注释的示例代码供您学习.

$(function() {

  // canvas related variables
  var canvas = document.getElementById("canvas");
  var ctx = canvas.getContext("2d");
  var $canvas = $("#canvas");
  var canvasOffset = $canvas.offset();
  var offsetX = canvasOffset.left;
  var offsetY = canvasOffset.top;

  // dom element to indicate if mouse is inside/outside line
  var $hit = $("#hit");

  // determine how close the mouse must be to the line
  // for the mouse to be inside the line
  var tolerance = 5;

  // define the starting & ending points of the line
  var line = {
    x0: 50,
    y0: 50,
    x1: 100,
    y1: 100
  };

  // set the fillstyle of the canvas
  ctx.fillStyle = "red";

  // draw the line for the first time
  draw(line);

  // function to draw the line
  // and optionally draw a dot when the mouse is inside
  function draw(line, mouseX, mouseY, lineX, lineY) {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.beginPath();
    ctx.moveTo(line.x0, line.y0);
    ctx.lineTo(line.x1, line.y1);
    ctx.stroke();
    if (mouseX && lineX) {
      ctx.beginPath();
      ctx.arc(lineX, lineY, tolerance, 0, Math.PI * 2);
      ctx.closePath();
      ctx.fill();
    }
  }

  // calculate the point on the line that's 
  // nearest to the mouse position
  function linepointNearestMouse(line, x, y) {
    //
    lerp = function(a, b, x) {
      return (a + x * (b - a));
    };
    var dx = line.x1 - line.x0;
    var dy = line.y1 - line.y0;
    var t = ((x - line.x0) * dx + (y - line.y0) * dy) / (dx * dx + dy * dy);
    var lineX = lerp(line.x0, line.x1, t);
    var lineY = lerp(line.y0, line.y1, t);
    return ({
      x: lineX,
      y: lineY
    });
  };

  // handle mousemove events
  // calculate how close the mouse is to the line
  // if that distance is less than tolerance then
  // display a dot on the line
  function handleMousemove(e) {
    e.preventDefault();
    e.stopPropagation();
    mouseX = parseInt(e.clientX - offsetX);
    mouseY = parseInt(e.clientY - offsetY);
    if (mouseX < line.x0 || mouseX > line.x1) {
      $hit.text("Outside");
      draw(line);
      return;
    }
    var linepoint = linepointNearestMouse(line, mouseX, mouseY);
    var dx = mouseX - linepoint.x;
    var dy = mouseY - linepoint.y;
    var distance = Math.abs(Math.sqrt(dx * dx + dy * dy));
    if (distance < tolerance) {
      $hit.text("Inside the line");
      draw(line, mouseX, mouseY, linepoint.x, linepoint.y);
    } else {
      $hit.text("Outside");
      draw(line);
    }
  }

  // tell the browser to call handleMousedown
  // whenever the mouse moves
  $("#canvas").mousemove(function(e) {
    handleMousemove(e);
  });

}); // end $(function(){});

关于命中测试路径:

如果使用路径命令创建路径,则可以使用context.isPointInPath(mouseX,mouseY)检查鼠标是否在路径中.context.isPointInPath不适用于行但是因为行理论上具有零宽度来"击中".