javascript - Canvas - 如何在新的 "route"上从单击到单击绘制线条并更改颜色

Question

我有一个 Canvas (见下图)，我已经被困了一段时间试图在用户点击 Canvas 内部时绘制的圆圈之间画线。

从照片中的示例可以看出，这也是我希望在 Canvas 中包含的内容:

用户点击蓝色 - 首先点蓝色 (x)，继续沿着网格在 Canvas 内点击，添加更多蓝色 (x's)，它们之间有蓝线。(我也不知道如何画 X 而不是我目前使用的圆圈)

用户点击红色 - 从第一个点红色 (o) 开始，继续沿着网格在 Canvas 内点击，添加更多红色 (o)，它们之间有红线。

用户点击“Sterge” - Canvas 清除，网格保留。

[ ]到目前为止我的代码:

var needFirstPoint = true;
var lineTo = [{}];

function drawNextLine(ctx, x, y) {
    if (needFirstPoint) {
        ctx.lineWidth = 2;
        ctx.beginPath();
        ctx.moveTo(x, y);
        needFirstPoint = false;

    }
    else {
        ctx.beginPath();
        ctx.lineTo(x, y);
        ctx.stroke();
    }
}

   $(document).ready(function () {
    var canvas = $('#myCanvas').get(0);
    if (!canvas.getContext) { return; }
    var ctx = canvas.getContext('2d');

    var drawGrid = function (w, h, id) {
        ctx.canvas.width = w;
        ctx.canvas.height = h;
        ctx.lineWidth = .1;

        for (x = 15; x <= w; x += 60) {
            ctx.moveTo(x, 0);
            ctx.lineTo(x, h);
            for (y = 20; y <= h; y += 20) {
                ctx.moveTo(0, y);
                ctx.lineTo(w, y);
            }
        }
        ctx.stroke();

    };

    drawGrid(450, 280, "myCanvas");

    var drawChart = function () {
        ctx.arc(lineTo[lineTo.length - 1].x, lineTo[lineTo.length - 1].y, 6, 0, Math.PI * 2, false)
        ctx.stroke();
    }

    drawChart();

    document.getElementById('move').addEventListener('click', function () {

        $('#myCanvas').on('click', function (e) {

            var offset = $(this).offset();
            var x = e.pageX - offset.left;
            var y = e.pageY - offset.top;
            ctx.strokeStyle = "red";
            drawNextLine(ctx, x, y);

            lineTo.push({ x: x, y: y });
            drawChart();

        });
    });

    document.getElementById('move1').addEventListener('click', function () {

        $('#myCanvas').on('click', function (e) {

            var offset = $(this).offset();
            var x = e.pageX - offset.left;
            var y = e.pageY - offset.top;
            ctx.strokeStyle = "blue";
            drawNextLine1(ctx, x, y);

            lineTo.push({ x: x, y: y });
            drawChart();

        });
    });

});

谢谢。

Answer 1

Ì简化了您的代码。我希望你不介意。接下来是我的代码。我希望这就是您想要的。

var lineTo = [];

$(document).ready(function() {
  var canvas = $("#myCanvas").get(0);
  if (!canvas.getContext) {
    return;
  }
  var ctx = canvas.getContext("2d");

  var drawGrid = function(w, h, id) {
    ctx.canvas.width = w;
    ctx.canvas.height = h;
    ctx.lineWidth = 0.1;
    ctx.beginPath();
    for (x = 15; x <= w; x += 60) {
      ctx.moveTo(x, 0);
      ctx.lineTo(x, h);
      for (y = 20; y <= h; y += 20) {
        ctx.moveTo(0, y);
        ctx.lineTo(w, y);
      }
    }
    ctx.stroke();
  };

  drawGrid(450, 280, "myCanvas");
  
  

  ctx.lineWidth = 1;
  
  

  var drawChart = function(x, y) {
    ctx.beginPath();
    ctx.arc(x, y, 6, 0, Math.PI * 2);
    ctx.strokeStyle = "red";
    ctx.stroke();
  };

  $("#myCanvas").on("click", function(e) {
    var offset = $(this).offset();
    var x = e.pageX - offset.left;
    var y = e.pageY - offset.top;

    drawChart(x, y);

    if (lineTo.length > 0) {
      var last = lineTo[lineTo.length - 1];
      ctx.beginPath();
      ctx.moveTo(last.x, last.y);
      ctx.lineTo(x, y);
      ctx.strokeStyle = "blue";
      ctx.stroke();
    }

    lineTo.push({ x: x, y: y });
  });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<canvas id="myCanvas"></canas>

更新

OP 正在评论:

I need to have 2 buttons : Left and Right. When I click on Left, the Right path is stopped and Left path begins from a independent point.

这个我不是很懂。这是我的理解:

我知道你需要一个按钮来删除最后一个点 sterge。

您还需要一个按钮 dreapta 来开始一条新路径。

这是我的代码。请阅读评论。

//this is an array of arrays
//when I click on the canvas a new point is pushed on the last array of this array
var ry = [[]];


var canvas = document.querySelector("#myCanvas");
let w = (canvas.width = 450);
let h = (canvas.height = 280);

var ctx = canvas.getContext("2d");

drawGrid();



myCanvas.addEventListener("click", e => {
  var offset = canvas.getBoundingClientRect();
  var x = e.clientX - offset.left;
  var y = e.clientY - offset.top;
  //a new point is pushed on the last array of ry
  ry[ry.length - 1].push({ x: x, y: y });
  // delete everything
  ctx.clearRect(0, 0, w, h);
  // draw everything
  drawGrid();
  drawChart();
});

sterge.addEventListener("click", e => {
  //when sterge is clicked the last point from the last array is deleted
  if (ry[ry.length - 1].length > 0) {
    ry[ry.length - 1].pop();
  } else {
    //if the last array is empty I delete this array 
    ry.pop();
    //and then I delete the last point from the last array
    ry[ry.length - 1].pop();
  }
  // delete everything
  ctx.clearRect(0, 0, w, h);
   // draw everything
  drawGrid();
  drawChart();
});

dreapta.addEventListener("click", e => {
  //when dreapta is clicked, a new array is pushed into the ry
  ry.push([]);
});

function drawGrid() {
  ctx.strokeStyle = "black";
  ctx.lineWidth = 0.1;
  ctx.beginPath();
  for (x = 15; x <= w; x += 60) {
    ctx.moveTo(x, 0);
    ctx.lineTo(x, h);
    for (y = 20; y <= h; y += 20) {
      ctx.moveTo(0, y);
      ctx.lineTo(w, y);
    }
  }
  ctx.stroke();
}

function drawChart() {
  ctx.lineWidth = 1;
  // for every array in the ry array
  for (let index = 0; index < ry.length; index++) {
    // for every point in the ry[index]
    for (let i = 0; i < ry[index].length; i++) {
      let l = ry[index][i];
      // draw the circle
      drawCircle(l.x, l.y);
      // draw the line
      if (i > 0) {
        let last = ry[index][i - 1];
        ctx.beginPath();
        ctx.moveTo(last.x, last.y);
        ctx.lineTo(l.x, l.y);
        ctx.strokeStyle = "blue";
        ctx.stroke();
      }
    }
  }
}

function drawCircle(x, y) {
  ctx.beginPath();
  ctx.arc(x, y, 6, 0, Math.PI * 2);
  ctx.strokeStyle = "red";
  ctx.stroke();
}

<canvas id="myCanvas"></canvas>
<p><input type="button" value="dreapta" id="dreapta" /> 
<input type="button" value="sterge" id="sterge" />
</p>