在鼠标悬停在画布上的形状/位置(坐标)上时显示工具提示

Question

当鼠标悬停在画布上的某些位置时，我正在尝试显示相应的工具提示。例如，当画布上的鼠标位置位于坐标 （100,100） 处时，将显示工具提示 1。当鼠标位置为 （200,200） 时，显示工具提示 2 等，

我已经添加了事件侦听器来检测鼠标移动并获取鼠标位置。这是我的部分：

window.addEventListener('mousemove',hover,false);
function getMousePos (canvas, event) {
    var rect = canvas.getBoundingClientRect();
    return {
        x: event.clientX - rect.left,
        y: event.clientY - rect.top
    };
}
function hover (event){
    pos = getMousePos(canvas,event);
    if (condition to detect mouse hover)
    //display tooltip_function (this is the function that I don't know how to implement)
}

Answer 1

您可以像这样测试鼠标是否位于其中一个圆形热点上：

var hotspots=[
    {x:100,y:100,radius:20,tip:'You are over 100,100'},
    {x:100,y:200,radius:20,tip:'You are over 100,200'},
];
var dx=mouseX-hotspot[0].x;
var dy=mouseY-hotspot[0].y;
if (dx * dx + dy * dy < hotspot[0].radius * hotspot[0].radius) {
  // it's over hotspot[0]
}

下面是示例代码和演示：

注意：您不需要像演示中那样显示圆形热点 - 这只是本演示

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 hotspots = [
  { x: 100, y: 100, radius: 20, tip: "You are over 100,100" },
  { x: 100, y: 200, radius: 20, tip: "You are over 100,200" },
];
draw();
$("#canvas").mousemove(function (e) {
  handleMouseMove(e);
});
function draw() {
  for (var i = 0; i < hotspots.length; i++) {
    var h = hotspots[i];
    ctx.beginPath();
    ctx.arc(h.x, h.y, h.radius, 0, Math.PI * 2);
    ctx.closePath();
    ctx.stroke();
  }
}
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);
  draw();
  for (var i = 0; i < hotspots.length; i++) {
    var h = hotspots[i];
    var dx = mouseX - h.x;
    var dy = mouseY - h.y;
    if (dx * dx + dy * dy < h.radius * h.radius) {
      ctx.fillText(h.tip, h.x, h.y);
    }
  }
}

body{ background-color: ivory; }
#canvas{border:1px solid red; margin:0 auto; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Hover over a hotspot circle</h4>
<canvas id="canvas" width=300 height=300></canvas>