js控制貝塞爾曲線程式碼例項

admin發表於2017-02-10
原文網址 : https://www.softwhy.com/article-717-1.html
JS線程
本章節分享一段程式碼例項，它實現了控制貝塞爾取消效果。

通過拖動幾個控制點即可實現，程式碼例項如下:

[HTML] 純文字檢視 複製程式碼
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="author" content="http://www.softwhy.com/" />
<title>螞蟻部落</title>
<style>
body {
  margin: 0;
  padding: 0;
}
canvas {
  background-color: #ccc;
}
</style>
</head>
<body>
<canvas id="canvas" width="1175" height="600"></canvas>
<script>
var canvas = document.getElementById("canvas"),
  context = canvas.getContext("2d"),
  isDragging = false,
  radius = 12;
/*先設定圓的四個點引數*/
circles = [{
  x: 200,
  y: 250,
  isSelected: false
}, {
  x: 280,
  y: 120,
  isSelected: false
}, {
  x: 380,
  y: 120,
  isSelected: false
}, {
  x: 450,
  y: 250,
  isSelected: false
}];
  
canvas.onmousedown = canvasClick;
canvas.onmouseup = stopDragging;
canvas.onmouseout = stopDragging;
canvas.onmousemove = moveDraw;
  
  
/*控制圓是否可以拖動*/
function stopDragging() {
  isDragging = false;
}
  
/*設定一個暫存點選圓引數*/
var previousCircle;
  
/*點選canvas*/
function canvasClick(e) {
  var clickX = e.pageX - canvas.offsetLeft;
  var clickY = e.pageY - canvas.offsetTop;
  for (i = circles.length - 1; i >= 0; i--) {
    var circle = circles[i];
    var distance = Math.sqrt(Math.pow(circle.x - clickX, 2) + Math.pow(circle.y - clickY, 2));
    if (distance <= radius) {
      if (previousCircle != null) {
        previousCircle.isSelected = false;
      }
      previousCircle = circle;
      isDragging = true;
      drawCircle();
      return;
    }
  
  }
  
}
  
  
/*滑鼠拖動圓點或者滑鼠選擇圓點*/
function moveDraw(e) {
  var moveX = e.pageX - canvas.offsetLeft;
  var moveY = e.pageY - canvas.offsetTop;
  if (isDragging == true) {
    previousCircle.x = moveX;
    previousCircle.y = moveY;
    drawCircle();
  } else {
    canvas.style.cursor = "default";
    for (i = circles.length - 1; i >= 0; i--) {
      var circle = circles[i];
      var distance = Math.sqrt(Math.pow(circle.x - moveX, 2) + Math.pow(circle.y - moveY, 2));
      if (distance <= radius) {
        circle.isSelected = true;
        canvas.style.cursor = "move";
      } else {
        circle.isSelected = false;
  
      }
    }
    drawCircle();
  }
  
}
  
  
  
/*繪製圓、線條、曲線*/
drawCircle()
  
function drawCircle() {
  context.clearRect(0, 0, canvas.width, canvas.height);
  context.globalAlpha = 0.85;
  //連線
  context.beginPath();
  context.moveTo(circles[0].x, circles[0].y);
  context.lineTo(circles[1].x, circles[1].y);
  context.lineTo(circles[2].x, circles[2].y);
  context.lineTo(circles[3].x, circles[3].y);
  context.lineWidth = 3;
  context.strokeStyle = "#ffffff";
  context.stroke();
  
  for (i = 0; i < circles.length; i++) {
    var circle = circles<i>
      //畫圓
    context.beginPath();
    context.arc(circle.x, circle.y, radius, 0, Math.PI * 2);
    context.strokeStyle = "#ffffff";
    context.lineWidth = 4;
    if (circle.isSelected == true) {
      context.fillStyle = "#00ff00";
    } else {
      context.fillStyle = "#ff0000";
    }
    context.fill();
    context.stroke();
  }
  /*二次貝塞爾曲線*/
  context.beginPath();
  context.moveTo(circles[0].x, circles[0].y);
  context.bezierCurveTo(circles[1].x, circles[1].y, circles[2].x, circles[2].y, circles[3].x, circles[3].y);
  context.lineWidth = 4.5;
  context.strokeStyle = 'yellow';
  context.stroke();
  xy_text()
}
  
/*繪製座標*/
function xy_text() {
  console.log(circles)
  for (i = 0; i < circles.length; i++) {
    context.beginPath();
    context.font = '12pt Arial';
    context.fillStyle = "#0000ff";
    var x_text = Math.floor(circles[i].x);
    var y_text = Math.floor(circles[i].y);
    context.fillText(x_text + "," + y_text, circles[i].x, circles[i].y + 30);
    context.closePath();
  }
}
</script>
</body>
</html>

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