CanvasRenderingContext2D.rotate()

CanvasRenderingContext2D.rotate() 是 Canvas 2D API 在变换矩阵中增加旋转的方法。角度变量表示一个顺时针旋转角度并且用弧度表示。

语法

void ctx.rotate(angle);

参数

angle
顺时针旋转的弧度。如果你想通过角度值计算，可以使用公式： degree * Math.PI / 180 。

旋转中心点一直是 canvas 的起始点。 如果想改变中心点，我们可以通过 translate() 方法移动 canvas 。

示例

使用 rotate 方法

这是一段使用 rotate 方法的简单的代码片段。

HTML

<canvas id="canvas"></canvas>

JavaScript

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

ctx.rotate(45 * Math.PI / 180);
ctx.fillRect(70,0,100,30);

// reset current transformation matrix to the identity matrix
ctx.setTransform(1, 0, 0, 1, 0, 0);

修改下面的代码并在线查看 canvas 的变化：

Playable code
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.rotate(45 * Math.PI / 180);
ctx.fillRect(70,0,100,30);
ctx.setTransform(1, 0, 0, 1, 0, 0);</textarea>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

规范描述

规范 状态 注释
HTML Living Standard
CanvasRenderingContext2D.rotate		 Living Standard  

浏览器兼容性

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

特性 Chrome Firefox (Gecko) Internet Explorer Opera Safari
基础支持 (Yes) (Yes) (Yes) (Yes) (Yes)
特性 Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
基础支持 (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

参见

相关主题
  1. CanvasRenderingContext2D
  2. 属性
    1. canvas
    2. currentTransform
    3. direction
    4. fillStyle
    5. filter
    6. font
    7. globalAlpha
    8. globalCompositeOperation
    9. imageSmoothingEnabled
    10. imageSmoothingQuality
    11. lineCap
    12. lineDashOffset
    13. lineJoin
    14. lineWidth
    15. miterLimit
    16. shadowBlur
    17. shadowColor
    18. shadowOffsetX
    19. shadowOffsetY
    20. strokeStyle
    21. textAlign
    22. textBaseline
  3. 方法
    1. addHitRegion()
    2. arc()
    3. arcTo()
    4. beginPath()
    5. bezierCurveTo()
    6. clearHitRegions()
    7. clearRect()
    8. clip()
    9. closePath()
    10. createImageData()
    11. createLinearGradient()
    12. createPattern()
    13. createRadialGradient()
    14. drawFocusIfNeeded()
    15. drawImage()
    16. drawWidgetAsOnScreen()
    17. drawWindow()
    18. ellipse()
    19. fill()
    20. fillRect()
    21. fillText()
    22. getImageData()
    23. getLineDash()
    24. isPointInPath()
    25. isPointInStroke()
    26. lineTo()
    27. measureText()
    28. moveTo()
    29. putImageData()
    30. quadraticCurveTo()
    31. rect()
    32. removeHitRegion()
    33. resetTransform()
    34. restore()
    35. rotate()
    36. save()
    37. scale()
    38. scrollPathIntoView()
    39. setLineDash()
    40. setTransform()
    41. stroke()
    42. strokeRect()
    43. strokeText()
    44. transform()
    45. translate()