javascript - 如何使用 HTML 5 Canvas 沿着弧形路径绘制文本？

Question

我想像这个 flash 动画一样绘制 Canvas 图形: http://www.cci.com.tr/tr/bizi-taniyin/tarihcemiz/

我画了六个弧线，我想在这些弧线上写六个字。有什么想法吗？

Answer 1

我有一个 jsFiddle 可以将文本应用于任意贝塞尔曲线定义。享受 http://jsfiddle.net/Makallus/hyyvpp8g/

var first = true;
startIt();


function startIt() {
  canvasDiv = document.getElementById('canvasDiv');
  canvasDiv.innerHTML = '<canvas id="layer0" width="300" height="300"></canvas>'; //for IE
  canvas = document.getElementById('layer0');
  ctx = canvas.getContext('2d');
  ctx.fillStyle = "black";
  ctx.font = "18px arial black";
  curve = document.getElementById('curve');
  curveText = document.getElementById('text');
  $(curve).keyup(function(e) {
    changeCurve();
  });
  $(curveText).keyup(function(e) {
    changeCurve();
  });




  if (first) {
    changeCurve();
    first = false;
  }

}

function changeCurve() {
  points = curve.value.split(',');
  if (points.length == 8) drawStack();

}

function drawStack() {
  Ribbon = {
    maxChar: 50,
    startX: points[0],
    startY: points[1],
    control1X: points[2],
    control1Y: points[3],
    control2X: points[4],
    control2Y: points[5],
    endX: points[6],
    endY: points[7]
  };

  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.save();
  ctx.beginPath();

  ctx.moveTo(Ribbon.startX, Ribbon.startY);
  ctx.bezierCurveTo(Ribbon.control1X, Ribbon.control1Y,
    Ribbon.control2X, Ribbon.control2Y,
    Ribbon.endX, Ribbon.endY);

  ctx.stroke();
  ctx.restore();

  FillRibbon(curveText.value, Ribbon);
}

function FillRibbon(text, Ribbon) {

  var textCurve = [];
  var ribbon = text.substring(0, Ribbon.maxChar);
  var curveSample = 1000;


  xDist = 0;
  var i = 0;
  for (i = 0; i < curveSample; i++) {
    a = new bezier2(i / curveSample, Ribbon.startX, Ribbon.startY, Ribbon.control1X, Ribbon.control1Y, Ribbon.control2X, Ribbon.control2Y, Ribbon.endX, Ribbon.endY);
    b = new bezier2((i + 1) / curveSample, Ribbon.startX, Ribbon.startY, Ribbon.control1X, Ribbon.control1Y, Ribbon.control2X, Ribbon.control2Y, Ribbon.endX, Ribbon.endY);
    c = new bezier(a, b);
    textCurve.push({
      bezier: a,
      curve: c.curve
    });
  }

  letterPadding = ctx.measureText(" ").width / 4;
  w = ribbon.length;
  ww = Math.round(ctx.measureText(ribbon).width);


  totalPadding = (w - 1) * letterPadding;
  totalLength = ww + totalPadding;
  p = 0;

  cDist = textCurve[curveSample - 1].curve.cDist;

  z = (cDist / 2) - (totalLength / 2);

  for (i = 0; i < curveSample; i++) {
    if (textCurve[i].curve.cDist >= z) {
      p = i;
      break;
    }
  }

  for (i = 0; i < w; i++) {
    ctx.save();
    ctx.translate(textCurve[p].bezier.point.x, textCurve[p].bezier.point.y);
    ctx.rotate(textCurve[p].curve.rad);
    ctx.fillText(ribbon[i], 0, 0);
    ctx.restore();

    x1 = ctx.measureText(ribbon[i]).width + letterPadding;
    x2 = 0;
    for (j = p; j < curveSample; j++) {
      x2 = x2 + textCurve[j].curve.dist;
      if (x2 >= x1) {
        p = j;
        break;
      }
    }




  }
} //end FillRibon

function bezier(b1, b2) {
  //Final stage which takes p, p+1 and calculates the rotation, distance on the path and accumulates the total distance
  this.rad = Math.atan(b1.point.mY / b1.point.mX);
  this.b2 = b2;
  this.b1 = b1;
  dx = (b2.x - b1.x);
  dx2 = (b2.x - b1.x) * (b2.x - b1.x);
  this.dist = Math.sqrt(((b2.x - b1.x) * (b2.x - b1.x)) + ((b2.y - b1.y) * (b2.y - b1.y)));
  xDist = xDist + this.dist;
  this.curve = {
    rad: this.rad,
    dist: this.dist,
    cDist: xDist
  };
}

function bezierT(t, startX, startY, control1X, control1Y, control2X, control2Y, endX, endY) {
  //calculates the tangent line to a point in the curve; later used to calculate the degrees of rotation at this point.
  this.mx = (3 * (1 - t) * (1 - t) * (control1X - startX)) + ((6 * (1 - t) * t) * (control2X - control1X)) + (3 * t * t * (endX - control2X));
  this.my = (3 * (1 - t) * (1 - t) * (control1Y - startY)) + ((6 * (1 - t) * t) * (control2Y - control1Y)) + (3 * t * t * (endY - control2Y));
}

function bezier2(t, startX, startY, control1X, control1Y, control2X, control2Y, endX, endY) {
  //Quadratic bezier curve plotter
  this.Bezier1 = new bezier1(t, startX, startY, control1X, control1Y, control2X, control2Y);
  this.Bezier2 = new bezier1(t, control1X, control1Y, control2X, control2Y, endX, endY);
  this.x = ((1 - t) * this.Bezier1.x) + (t * this.Bezier2.x);
  this.y = ((1 - t) * this.Bezier1.y) + (t * this.Bezier2.y);
  this.slope = new bezierT(t, startX, startY, control1X, control1Y, control2X, control2Y, endX, endY);

  this.point = {
    t: t,
    x: this.x,
    y: this.y,
    mX: this.slope.mx,
    mY: this.slope.my
  };
}

function bezier1(t, startX, startY, control1X, control1Y, control2X, control2Y) {
  //linear bezier curve plotter; used recursivly in the quadratic bezier curve calculation
  this.x = ((1 - t) * (1 - t) * startX) + (2 * (1 - t) * t * control1X) + (t * t * control2X);
  this.y = ((1 - t) * (1 - t) * startY) + (2 * (1 - t) * t * control1Y) + (t * t * control2Y);

}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<table>
  <TR>
    <TH>Bezier Curve</TH>
    <TD>
      <input size="80" type="text" id="curve" name="curve" value="99.2,177.2,130.02,60.0,300.5,276.2,300.7,176.2">
    </TD>
  </TR>
  <TR>
    <TH>Text</TH>
    <TD>
      <input size="80" type="text" id="text" name="text" value="testing 1234567890">
    </TD>
  </TR>
  <TR>
    <TD colspan=2>
      <div id="canvasDiv"></div>
    </TD>
  </TR>
</table>