CanvasRenderingContext2D
<canvas>
element.To get an object of this interface, call getContext()
on a <canvas> element
, supplying "2d" as the argument:
var canvas = document.getElementById('mycanvas'); // in your HTML this element appears as <canvas id="mycanvas"></canvas> var ctx = canvas.getContext('2d');
Once you have the 2D rendering context for a canvas, you can draw within it. For example:
ctx.fillStyle = "rgb(200,0,0)"; // sets the color to fill in the rectangle with ctx.fillRect(10, 10, 55, 50); // draws the rectangle at position 10, 10 with a width of 55 and a height of 50
See the properties and methods in the sidebar and below. The canvas tutorial has more information, examples, and resources as well.
Drawing rectangles
There are three methods that immediately draw rectangles to the bitmap.
CanvasRenderingContext2D.clearRect()
- Sets all pixels in the rectangle defined by starting point (x, y) and size (width, height) to transparent black, erasing any previously drawn content.
CanvasRenderingContext2D.fillRect()
- Draws a filled rectangle at (x, y) position whose size is determined by width and height.
CanvasRenderingContext2D.strokeRect()
- Paints a rectangle which has a starting point at (x, y) and has a w width and an h height onto the canvas, using the current stroke style.
Drawing text
The following methods are provided for drawing text. See also the TextMetrics
object for text properties.
CanvasRenderingContext2D.fillText()
- Draws (fills) a given text at the given (x,y) position.
CanvasRenderingContext2D.strokeText()
- Draws (strokes) a given text at the given (x, y) position.
CanvasRenderingContext2D.measureText()
- Returns a
TextMetrics
object.
Line styles
The following methods and properties control how lines are drawn.
CanvasRenderingContext2D.lineWidth
- Width of lines. Default
1.0
CanvasRenderingContext2D.lineCap
- Type of endings on the end of lines. Possible values:
butt
(default),round
,square
. CanvasRenderingContext2D.lineJoin
- Defines the type of corners where two lines meet. Possible values:
round
,bevel
,miter
(default). CanvasRenderingContext2D.miterLimit
- Miter limit ratio. Default
10
. CanvasRenderingContext2D.getLineDash()
- Returns the current line dash pattern array containing an even number of non-negative numbers.
CanvasRenderingContext2D.setLineDash()
- Sets the current line dash pattern.
CanvasRenderingContext2D.lineDashOffset
- Specifies where to start a dash array on a line.
Text styles
The following properties control how text is laid out.
CanvasRenderingContext2D.font
- Font setting. Default value
10px sans-serif
. CanvasRenderingContext2D.textAlign
- Text alignment setting. Possible values:
start
(default),end
,left
,right
orcenter
. CanvasRenderingContext2D.textBaseline
- Baseline alignment setting. Possible values:
top
,hanging
,middle
,alphabetic
(default),ideographic
,bottom
. CanvasRenderingContext2D.direction
- Directionality. Possible values:
ltr, rtl
,inherit
(default).
Fill and stroke styles
Fill styling is used for colors and styles inside shapes and stroke styling is used for the lines around shapes.
CanvasRenderingContext2D.fillStyle
- Color or style to use inside shapes. Default
#000
(black). CanvasRenderingContext2D.strokeStyle
- Color or style to use for the lines around shapes. Default
#000
(black).
Gradients and patterns
CanvasRenderingContext2D.createLinearGradient()
- Creates a linear gradient along the line given by the coordinates represented by the parameters.
CanvasRenderingContext2D.createRadialGradient()
- Creates a radial gradient given by the coordinates of the two circles represented by the parameters.
CanvasRenderingContext2D.createPattern()
- Creates a pattern using the specified image (a
CanvasImageSource
). It repeats the source in the directions specified by the repetition argument. This method returns aCanvasPattern
.
Shadows
CanvasRenderingContext2D.shadowBlur
- Specifies the blurring effect. Default
0
CanvasRenderingContext2D.shadowColor
- Color of the shadow. Default fully-transparent black.
CanvasRenderingContext2D.shadowOffsetX
- Horizontal distance the shadow will be offset. Default 0.
CanvasRenderingContext2D.shadowOffsetY
- Vertical distance the shadow will be offset. Default 0.
Paths
The following methods can be used to manipulate paths of objects.
CanvasRenderingContext2D.beginPath()
- Starts a new path by emptying the list of sub-paths. Call this method when you want to create a new path.
CanvasRenderingContext2D.closePath()
- Causes the point of the pen to move back to the start of the current sub-path. It tries to draw a straight line from the current point to the start. If the shape has already been closed or has only one point, this function does nothing.
CanvasRenderingContext2D.moveTo()
- Moves the starting point of a new sub-path to the (x, y) coordinates.
CanvasRenderingContext2D.lineTo()
- Connects the last point in the subpath to the
x, y
coordinates with a straight line. CanvasRenderingContext2D.bezierCurveTo()
- Adds a cubic Bézier curve to the path. It requires three points. The first two points are control points and the third one is the end point. The starting point is the last point in the current path, which can be changed using
moveTo()
before creating the Bézier curve. CanvasRenderingContext2D.quadraticCurveTo()
- Adds a quadratic Bézier curve to the current path.
CanvasRenderingContext2D.arc()
- Adds an arc to the path which is centered at (x, y) position with radius r starting at startAngle and ending at endAngle going in the given direction by anticlockwise (defaulting to clockwise).
CanvasRenderingContext2D.arcTo()
- Adds an arc to the path with the given control points and radius, connected to the previous point by a straight line.
CanvasRenderingContext2D.ellipse()
- Adds an ellipse to the path which is centered at (x, y) position with the radii radiusX and radiusY starting at startAngle and ending at endAngle going in the given direction by anticlockwise (defaulting to clockwise).
CanvasRenderingContext2D.rect()
- Creates a path for a rectangle at position (x, y) with a size that is determined by width and height.
Drawing paths
CanvasRenderingContext2D.fill()
- Fills the subpaths with the current fill style.
CanvasRenderingContext2D.stroke()
- Strokes the subpaths with the current stroke style.
CanvasRenderingContext2D.drawFocusIfNeeded()
- If a given element is focused, this method draws a focus ring around the current path.
CanvasRenderingContext2D.scrollPathIntoView()
- Scrolls the current path or a given path into the view.
CanvasRenderingContext2D.clip()
- Creates a clipping path from the current sub-paths. Everything drawn after
clip()
is called appears inside the clipping path only. For an example, see Clipping paths in the Canvas tutorial. CanvasRenderingContext2D.isPointInPath()
- Reports whether or not the specified point is contained in the current path.
CanvasRenderingContext2D.isPointInStroke()
- Reports whether or not the specified point is inside the area contained by the stroking of a path.
Transformations
Objects in the CanvasRenderingContext2D
rendering context have a current transformation matrix and methods to manipulate it. The transformation matrix is applied when creating the current default path, painting text, shapes and Path2D
objects. The methods listed below remain for historical and compatibility reasons as SVGMatrix
objects are used in most parts of the API nowadays and will be used in the future instead.
CanvasRenderingContext2D.currentTransform
- Current transformation matrix (
SVGMatrix
object). CanvasRenderingContext2D.rotate()
- Adds a rotation to the transformation matrix. The angle argument represents a clockwise rotation angle and is expressed in radians.
CanvasRenderingContext2D.scale()
- Adds a scaling transformation to the canvas units by x horizontally and by y vertically.
CanvasRenderingContext2D.translate()
- Adds a translation transformation by moving the canvas and its origin x horzontally and y vertically on the grid.
CanvasRenderingContext2D.transform()
- Multiplies the current transformation matrix with the matrix described by its arguments.
CanvasRenderingContext2D.setTransform()
- Resets the current transform to the identity matrix, and then invokes the
transform()
method with the same arguments. CanvasRenderingContext2D.resetTransform()
- Resets the current transform by the identity matrix.
Compositing
CanvasRenderingContext2D.globalAlpha
- Alpha value that is applied to shapes and images before they are composited onto the canvas. Default
1.0
(opaque). CanvasRenderingContext2D.globalCompositeOperation
- With
globalAlpha
applied this sets how shapes and images are drawn onto the existing bitmap.
Drawing images
CanvasRenderingContext2D.drawImage()
- Draws the specified image. This method is available in multiple formats, providing a great deal of flexibility in its use.
Pixel manipulation
See also the ImageData
object.
CanvasRenderingContext2D.createImageData()
- Creates a new, blank
ImageData
object with the specified dimensions. All of the pixels in the new object are transparent black. CanvasRenderingContext2D.getImageData()
- Returns an
ImageData
object representing the underlying pixel data for the area of the canvas denoted by the rectangle which starts at (sx, sy) and has an sw width and sh height. CanvasRenderingContext2D.putImageData()
- Paints data from the given
ImageData
object onto the bitmap. If a dirty rectangle is provided, only the pixels from that rectangle are painted.
Image smoothing
CanvasRenderingContext2D.imageSmoothingEnabled
- Image smoothing mode; if disabled, images will not be smoothed if scaled.
The canvas state
The CanvasRenderingContext2D
rendering context contains a variety of drawing style states (attributes for line styles, fill styles, shadow styles, text styles). The following methods help you to work with that state:
CanvasRenderingContext2D.save()
- Saves the current drawing style state using a stack so you can revert any change you make to it using
restore()
. CanvasRenderingContext2D.restore()
- Restores the drawing style state to the last element on the 'state stack' saved by
save()
. CanvasRenderingContext2D.canvas
- A read-only back-reference to the
HTMLCanvasElement
. Might benull
if it is not associated with a<canvas>
element.
Hit regions
CanvasRenderingContext2D.addHitRegion()
- Adds a hit region to the canvas.
CanvasRenderingContext2D.removeHitRegion()
- Removes the hit region with the specified
id
from the canvas. CanvasRenderingContext2D.clearHitRegions()
- Removes all hit regions from the canvas.
Non-standard APIs
Blink and WebKit
Most of these APIs are deprecated and will be removed in the future.
-
CanvasRenderingContext2D.clearShadow()
- Removes all shadow settings like
CanvasRenderingContext2D.shadowColor
andCanvasRenderingContext2D.shadowBlur
. -
CanvasRenderingContext2D.drawImageFromRect()
- This is redundant with an equivalent overload of
drawImage
. -
CanvasRenderingContext2D.setAlpha()
- Use
CanvasRenderingContext2D.globalAlpha
instead. -
CanvasRenderingContext2D.setCompositeOperation()
- Use
CanvasRenderingContext2D.globalCompositeOperation
instead. -
CanvasRenderingContext2D.setLineWidth()
- Use
CanvasRenderingContext2D.lineWidth
instead. -
CanvasRenderingContext2D.setLineJoin()
- Use
CanvasRenderingContext2D.lineJoin
instead. -
CanvasRenderingContext2D.setLineCap()
- Use
CanvasRenderingContext2D.lineCap
instead. -
CanvasRenderingContext2D.setMiterLimit()
- Use
CanvasRenderingContext2D.miterLimit
instead. -
CanvasRenderingContext2D.setStrokeColor()
- Use
CanvasRenderingContext2D.strokeStyle
instead. -
CanvasRenderingContext2D.setFillColor()
- Use
CanvasRenderingContext2D.fillStyle
instead. -
CanvasRenderingContext2D.setShadow()
- Use
CanvasRenderingContext2D.shadowColor
andCanvasRenderingContext2D.shadowBlur
instead. -
CanvasRenderingContext2D.webkitLineDash
- Use
CanvasRenderingContext2D.getLineDash()
andCanvasRenderingContext2D.setLineDash()
instead. -
CanvasRenderingContext2D.webkitLineDashOffset
- Use
CanvasRenderingContext2D.lineDashOffset
instead. -
CanvasRenderingContext2D.webkitImageSmoothingEnabled
- Use
CanvasRenderingContext2D.imageSmoothingEnabled
instead.
Blink only
-
CanvasRenderingContext2D.getContextAttributes()
- Inspired by the same
WebGLRenderingContext
method it returns anCanvas2DContextAttributes
object that contains the attributes "storage" to indicate which storage is used ("persistent" by default) and the attribute "alpha" (true
by default) to indicate that transparency is used in the canvas. -
CanvasRenderingContext2D.isContextLost()
- Inspired by the same
WebGLRenderingContext
method it returnstrue
if the Canvas context has been lost, orfalse
if not.
WebKit only
-
CanvasRenderingContext2D.webkitBackingStorePixelRatio
- The backing store size in relation to the canvas element. See High DPI Canvas.
-
CanvasRenderingContext2D.webkitGetImageDataHD
- Intended for HD backing stores, but removed from canvas specifications.
-
CanvasRenderingContext2D.webkitPutImageDataHD
- Intended for HD backing stores, but removed from canvas specifications.
Gecko only
-
CanvasRenderingContext2D.filter
- CSS and SVG filters as Canvas APIs. Likely to be standardized in a new version of the specification.
Prefixed APIs
-
CanvasRenderingContext2D.mozCurrentTransform
- Sets or gets the current transformation matrix, see
CanvasRenderingContext2D.currentTransform
. -
CanvasRenderingContext2D.mozCurrentTransformInverse
- Sets or gets the current inversed transformation matrix.
-
CanvasRenderingContext2D.mozFillRule
- The fill rule to use. This must be one of
evenodd
ornonzero
(default). -
CanvasRenderingContext2D.mozImageSmoothingEnabled
- See
CanvasRenderingContext2D.imageSmoothingEnabled
. -
CanvasRenderingContext2D.mozDash
- An array which specifies the lengths of alternating dashes and gaps . Use
CanvasRenderingContext2D.getLineDash()
andCanvasRenderingContext2D.setLineDash()
instead. -
CanvasRenderingContext2D.mozDashOffset
- Specifies where to start a dash array on a line. . Use
CanvasRenderingContext2D.lineDashOffset
instead. -
CanvasRenderingContext2D.mozTextStyle
- Introduced in in Gecko 1.9, deprecated in favor of the
CanvasRenderingContext2D.font
property. -
CanvasRenderingContext2D.mozDrawText()
- This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0. Use
CanvasRenderingContext2D.strokeText()
orCanvasRenderingContext2D.fillText()
instead. -
CanvasRenderingContext2D.mozMeasureText()
- This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0. Use
CanvasRenderingContext2D.measureText()
instead. -
CanvasRenderingContext2D.mozPathText()
- This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
-
CanvasRenderingContext2D.mozTextAlongPath()
- This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
Internal APIs (chrome-context only)
-
CanvasRenderingContext2D.asyncDrawXULElement()
- Renders a region of a XUL element into the
canvas
. -
CanvasRenderingContext2D.drawWindow()
- Renders a region of a window into the
canvas
. The contents of the window's viewport are rendered, ignoring viewport clipping and scrolling. -
CanvasRenderingContext2D.demote()
- This causes a context that is currently using a hardware-accelerated backend to fallback to a software one. All state should be preserved.
Internet Explorer
-
CanvasRenderingContext2D.msFillRule
- The fill rule to use. This must be one of
evenodd
ornonzero
(default).
Specifications
Specification | Status | Comment |
---|---|---|
WHATWG HTML Living Standard The definition of 'CanvasRenderingContext2D' in that specification. |
Living Standard |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 1 | 1.5 (1.8) | 9 | 9 | 2 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | ? | ? | ? | ? | ? | ? |
Compatibility notes
- Starting with Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), specifying invalid values are now silently ignored for the following methods and properties:
translate()
,transform()
,rotate(),
scale(),
rect()
,clearRect()
,fillRect()
,strokeRect()
,lineTo()
,moveTo()
,quadraticCurveTo()
,arc()
,shadowOffsetX
,shadowOffsetY
,shadowBlur
.
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/canvasrenderingcontext2d