canvas繪製帶有刻度的座標系程式碼例項

admin發表於2017-03-01
Canvas

分享一段程式碼例項，它實現了繪製帶有刻度的座標系的功能。

程式碼例項如下:

[HTML] 純文字檢視 複製程式碼執行程式碼
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="author" content="http://www.softwhy.com/" />
<title>螞蟻部落</title>
</head>
<body>
<canvas id="canvas" width="500" height="500"></canvas>
<script>
var canvas = document.getElementById("canvas"),
  context = canvas.getContext('2d'),
 
 
  AXIS_MARGIN = 40,
  AXIS_ORIGIN = {
    x: AXIS_MARGIN,
    y: canvas.height - AXIS_MARGIN
  },
  AXIS_TOP = AXIS_MARGIN,
  AXIS_RIGHT = canvas.width - AXIS_MARGIN,
 
 
  HORIZONTAL_TICK_SPACING = 10,
  VERTICAL_TICK_SPACING = 10,
 
  AXIS_WIDTH = AXIS_RIGHT - AXIS_ORIGIN.x,
  AXIS_HEIGHT = AXIS_ORIGIN.y - AXIS_TOP,
 
  NUM_VERTICAL_TICKS = AXIS_HEIGHT / VERTICAL_TICK_SPACING,
  NUM_HORIZONTAL_TICKS = AXIS_WIDTH / HORIZONTAL_TICK_SPACING,
 
  TICK_WIDTH = 10,
  TICKS_LINEWIDTH = 0.5,
  TICKS_COLOR = 'navy',
 
  AXIS_LINEWIDTH = 1.0,
  AXIS_COLOR = 'blue';
 
 
function drawGrid(color, stepx, stepy) {
 
}
 
function drawAxes() {
  context.save();
  context.strokeStyle = AXIS_COLOR;
  context.lineWidth = AXIS_LINEWIDTH;
 
  drawHorizontalAxis();
  drawVerticalAxis();
 
  context.lineWidth = 0.5;
  context.lineWidth = TICKS_LINEWIDTH;
  context.strokeStyle = TICKS_COLOR;
 
  drawVerticalAxisTicks();
  drawHorizontalAxisTicks();
 
  context.restore();
}
 
function drawHorizontalAxis() {
  context.beginPath();
  context.moveTo(AXIS_ORIGIN.x, AXIS_ORIGIN.y);
  context.lineTo(AXIS_RIGHT, AXIS_ORIGIN.y);
  context.stroke();
}
 
function drawVerticalAxis() {
  context.beginPath();
  context.moveTo(AXIS_ORIGIN.x, AXIS_ORIGIN.y);
  context.lineTo(AXIS_ORIGIN.x, AXIS_TOP);
  context.stroke();
}
 
function drawVerticalAxisTicks() {
  var deltaX;
 
  for (var i = 1; i < NUM_VERTICAL_TICKS; ++i) {
    context.beginPath();
    if (i % 5 === 0) deltaX = TICK_WIDTH;
    else deltaX = TICK_WIDTH / 2;
    context.moveTo(AXIS_ORIGIN.x - deltaX,
      AXIS_ORIGIN.y - i * VERTICAL_TICK_SPACING);
    context.lineTo(AXIS_ORIGIN.x + deltaX,
      AXIS_ORIGIN.y - i * VERTICAL_TICK_SPACING);
 
    context.stroke();
  }
}
 
function drawHorizontalAxisTicks() {
  var deltaY;
 
  for (var i = 1; i < NUM_HORIZONTAL_TICKS; ++i) {
    context.beginPath();
    if (i % 5 === 0) deltaY = TICK_WIDTH;
    else deltaY = TICK_WIDTH / 2;
    context.moveTo(AXIS_ORIGIN.x + i * HORIZONTAL_TICK_SPACING,
      AXIS_ORIGIN.y - deltaY);
    context.lineTo(AXIS_ORIGIN.x + i * HORIZONTAL_TICK_SPACING,
      AXIS_ORIGIN.y + deltaY);
 
    context.stroke();
  }
}
drawGrid('lightgray', 10, 10);
drawAxes();
</script>
</body>
</html>

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