CanvasRenderingContext2D
La interfaz CanvasRenderingContext2D
proporciona el contexto de renderizado 2D para la superficie de dibujo de un elemento <canvas>
.
Para obtener un objeto de esta interfaz, llama a getContext()
en un <canvas>
, proporcionando "2d" como argumento:
var canvas = document.getElementById('mycanvas');
var ctx = canvas.getContext('2d');
Una vez que tengas el contexto de renderizado 2D para un canvas, podrás dibujar en ella. Por ejemplo:
ctx.fillStyle = "rgb(200,0,0)";
ctx.fillRect(10, 10, 55, 50);
Mira las propiedades y métodos en la barra lateral. El tutorial de canvas tiene más información, ejemplos y recursos también.
Dibujando rectángulos
Hay 3 métodos que inmediatamente dibujan rectángulos en el bitmap.
CanvasRenderingContext2D.clearRect()
-
Establece todos los píxeles del rectangulo definido por los puntos (x, y) y tamaños (ancho, alto) a negro transparente, borrando cualquier contenido previo.
CanvasRenderingContext2D.fillRect()
-
Dibuja un rectángulo relleno en la posición (x, y) cuyo tamaño está determinado por la anchura y la altura.
CanvasRenderingContext2D.strokeRect()
(en-US)-
Dibuja un rectángulo que tiene como posición inicial (x, y) con un ancho w y altura h sobre el canvas, utilizando el estilo de trazo actual.
Dibujando texto
Los siguientes métodos se proporcionan para dibujar texto. Mira también el objeto TextMetrics
(en-US) para propiedades de texto.
CanvasRenderingContext2D.fillText()
(en-US)-
Dibuja (llena) un texto dado en una posición (x, y) dada.
CanvasRenderingContext2D.strokeText()
(en-US)-
Dibuja (trazas) un texto dado en una posición (x, y) dada.
CanvasRenderingContext2D.measureText()
(en-US)-
Devuelve el objeto
TextMetrics
(en-US).
Los estilos de línea
Los siguientes métodos y propiedades controlan como las líneas son dibujadas.
CanvasRenderingContext2D.lineWidth
(en-US)-
Ancho de líneas. Por defecto
1.0
CanvasRenderingContext2D.lineCap
-
Tipo de terminaciones en el final de las líneas. Posibles valores:
butt
(defecto),round
,square
. CanvasRenderingContext2D.lineJoin
(en-US)-
Define el tipo de esquinas donde dos líneas se encuentran. Pislbes valores:
round
,bevel
,miter
(defecto). CanvasRenderingContext2D.miterLimit
(en-US)-
Relación límite angular. Defecto
10
. CanvasRenderingContext2D.getLineDash()
(en-US)-
Devuelve la matriz patrón de trazos actual que contiene un número de par de números no negativos.
CanvasRenderingContext2D.setLineDash()
(en-US)-
Establece el patrón de trazos linea actual.
CanvasRenderingContext2D.lineDashOffset
(en-US)-
Especifica donde inicia una gama de instrumentos en una línea.
Estilos de texto
Las siguientes propiedades control como el texto es presentado.
CanvasRenderingContext2D.font
(en-US)-
Ajuste de fuente. Valor por defecto
10px sans-serif
. CanvasRenderingContext2D.textAlign
(en-US)-
Text alignment setting. Possible values:
start
(default),end
,left
,right
orcenter
. CanvasRenderingContext2D.textBaseline
(en-US)-
Baseline alignment setting. Possible values:
top
,hanging
,middle
,alphabetic
(default),ideographic
,bottom
. CanvasRenderingContext2D.direction
(en-US)-
Directionality. Possible values:
ltr, rtl
,inherit
(default).
Estilo del relleno y de los bordes
Fill styling es utilizado para estilizar los colores del relleno y los bordes de las formas.
CanvasRenderingContext2D.fillStyle
(en-US)-
Utilizado para dar color al relleno de las formas. Color por defecto
#000
(negro). CanvasRenderingContext2D.strokeStyle
(en-US)-
Utilizado para dar color al borde de las formas. Color por defecto
#000
(negro).
Degradados y patrones
CanvasRenderingContext2D.createLinearGradient()
(en-US)-
Creates a linear gradient along the line given by the coordinates represented by the parameters.
CanvasRenderingContext2D.createRadialGradient()
(en-US)-
Creates a radial gradient along the line given by the coordinates represented by the parameters.
CanvasRenderingContext2D.createPattern()
(en-US)-
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
(en-US).
Sombras
CanvasRenderingContext2D.shadowBlur
(en-US)-
Especifica el efecto de desenfoque. Predeterminado
0
CanvasRenderingContext2D.shadowColor
(en-US)-
Color de la sombra. Predeterminado totalmente transparente negro.
CanvasRenderingContext2D.shadowOffsetX
(en-US)-
Distancia horizontal del desplazamiento de la sombra. Predeterminado 0.
CanvasRenderingContext2D.shadowOffsetY
(en-US)-
Distancia vertical del desplazamiento de la sombra. Predeterminado 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()
(en-US)-
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()
(en-US)-
Moves the starting point of a new sub-path to the (x, y) coordinates.
CanvasRenderingContext2D.lineTo()
(en-US)-
Connects the last point in the subpath to the
x, y
coordinates with a straight line. CanvasRenderingContext2D.bezierCurveTo()
(en-US)-
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()
(en-US)-
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()
(en-US)-
Adds an arc to the path with the given control points and radius, connected to the previous point by a straight line.
CanvasRenderingContext2D.ellipse()
(en-US) Experimental-
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()
(en-US)-
Creates a path for a rectangle at position (x, y) with a size that is determined by width and height.
Drawing paths
CanvasRenderingContext2D.fill()
(en-US)-
Fills the subpaths with the current fill style.
CanvasRenderingContext2D.stroke()
(en-US)-
Strokes the subpaths with the current stroke style.
CanvasRenderingContext2D.drawFocusIfNeeded()
(en-US)-
If a given element is focused, this method draws a focus ring around the current path.
CanvasRenderingContext2D.scrollPathIntoView()
(en-US)-
Scrolls the current path or a given path into the view.
CanvasRenderingContext2D.clip()
(en-US)-
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()
(en-US)-
Reports whether or not the specified point is contained in the current path.
CanvasRenderingContext2D.isPointInStroke()
(en-US)-
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
(en-US) objects. The methods listed below remain for historical and compatibility reasons as SVGMatrix
(en-US) objects are used in most parts of the API nowadays and will be used in the future instead.
CanvasRenderingContext2D.currentTransform
(en-US)-
Current transformation matrix (
SVGMatrix
(en-US) 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()
(en-US)-
Adds a scaling transformation to the canvas units by x horizontally and by y vertically.
CanvasRenderingContext2D.translate()
(en-US)-
Adds a translation transformation by moving the canvas and its origin x horzontally and y vertically on the grid.
CanvasRenderingContext2D.transform()
(en-US)-
Multiplies the current transformation matrix with the matrix described by its arguments.
CanvasRenderingContext2D.setTransform()
(en-US)-
Resets the current transform to the identity matrix, and then invokes the
transform()
method with the same arguments. CanvasRenderingContext2D.resetTransform()
(en-US) Experimental-
Resets the current transform by the identity matrix.
Compositing
CanvasRenderingContext2D.globalAlpha
(en-US)-
Alpha value that is applied to shapes and images before they are composited onto the canvas. Default
1.0
(opaque). CanvasRenderingContext2D.globalCompositeOperation
(en-US)-
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
(en-US) object.
CanvasRenderingContext2D.createImageData()
(en-US)-
Creates a new, blank
ImageData
(en-US) object with the specified dimensions. All of the pixels in the new object are transparent black. CanvasRenderingContext2D.getImageData()
-
Returns an
ImageData
(en-US) 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()
(en-US)-
Paints data from the given
ImageData
(en-US) object onto the bitmap. If a dirty rectangle is provided, only the pixels from that rectangle are painted.
Image smoothing
CanvasRenderingContext2D.imageSmoothingEnabled
(en-US) Experimental-
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()
(en-US)-
Restores the drawing style state to the last element on the 'state stack' saved by
save()
. CanvasRenderingContext2D.canvas
(en-US)-
A read-only back-reference to the
HTMLCanvasElement
. Might benull
if it is not associated with a<canvas>
element.
Hit regions
CanvasRenderingContext2D.addHitRegion()
Experimental-
Adds a hit region to the canvas.
CanvasRenderingContext2D.removeHitRegion()
Experimental-
Removes the hit region with the specified
id
from the canvas. CanvasRenderingContext2D.clearHitRegions()
Experimental-
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.
-
Non-standard
CanvasRenderingContext2D.clearShadow()
-
Removes all shadow settings like
CanvasRenderingContext2D.shadowColor
(en-US) andCanvasRenderingContext2D.shadowBlur
(en-US). -
Non-standard
CanvasRenderingContext2D.drawImageFromRect()
-
This is redundant with an equivalent overload of
drawImage
. -
Non-standard
CanvasRenderingContext2D.setAlpha()
-
Use
CanvasRenderingContext2D.globalAlpha
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setCompositeOperation()
-
Use
CanvasRenderingContext2D.globalCompositeOperation
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setLineWidth()
-
Use
CanvasRenderingContext2D.lineWidth
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setLineJoin()
-
Use
CanvasRenderingContext2D.lineJoin
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setLineCap()
-
Use
CanvasRenderingContext2D.lineCap
instead. -
Non-standard
CanvasRenderingContext2D.setMiterLimit()
-
Use
CanvasRenderingContext2D.miterLimit
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setStrokeColor()
-
Use
CanvasRenderingContext2D.strokeStyle
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setFillColor()
-
Use
CanvasRenderingContext2D.fillStyle
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.setShadow()
-
Use
CanvasRenderingContext2D.shadowColor
(en-US) andCanvasRenderingContext2D.shadowBlur
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.webkitLineDash
-
Use
CanvasRenderingContext2D.getLineDash()
(en-US) andCanvasRenderingContext2D.setLineDash()
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.webkitLineDashOffset
-
Use
CanvasRenderingContext2D.lineDashOffset
(en-US) instead. -
Non-standard
CanvasRenderingContext2D.webkitImageSmoothingEnabled
-
Use
CanvasRenderingContext2D.imageSmoothingEnabled
(en-US) instead.
Blink only
-
Non-standard
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. -
Non-standard
CanvasRenderingContext2D.isContextLost()
-
Inspired by the same
WebGLRenderingContext
method it returnstrue
if the Canvas context has been lost, orfalse
if not.
WebKit only
-
Non-standard
CanvasRenderingContext2D.webkitBackingStorePixelRatio
-
The backing store size in relation to the canvas element. See High DPI Canvas.
-
Non-standard
CanvasRenderingContext2D.webkitGetImageDataHD
-
Intended for HD backing stores, but removed from canvas specifications.
-
Non-standard
CanvasRenderingContext2D.webkitPutImageDataHD
-
Intended for HD backing stores, but removed from canvas specifications.
Gecko only
-
Non-standard
CanvasRenderingContext2D.filter
(en-US) -
CSS and SVG filters as Canvas APIs. Likely to be standardized in a new version of the specification.
Prefixed APIs
-
Non-standard
CanvasRenderingContext2D.mozCurrentTransform
-
Sets or gets the current transformation matrix, see
CanvasRenderingContext2D.currentTransform
(en-US). -
Non-standard
CanvasRenderingContext2D.mozCurrentTransformInverse
-
Sets or gets the current inversed transformation matrix.
-
Non-standard
CanvasRenderingContext2D.mozFillRule
-
The fill rule to use. This must be one of
evenodd
ornonzero
(default). -
Non-standard
CanvasRenderingContext2D.mozImageSmoothingEnabled
-
Non-standard
Deprecated
CanvasRenderingContext2D.mozDash
-
An array which specifies the lengths of alternating dashes and gaps. Use
CanvasRenderingContext2D.getLineDash()
(en-US) andCanvasRenderingContext2D.setLineDash()
(en-US) instead. -
Non-standard
Deprecated
CanvasRenderingContext2D.mozDashOffset
-
Specifies where to start a dash array on a line. Use
CanvasRenderingContext2D.lineDashOffset
(en-US) instead. -
Non-standard
Deprecated
CanvasRenderingContext2D.mozTextStyle
-
Introduced in in Gecko 1.9, deprecated in favor of the
CanvasRenderingContext2D.font
(en-US) property. -
Non-standard
Deprecated
CanvasRenderingContext2D.mozDrawText()
-
This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0. Use
CanvasRenderingContext2D.strokeText()
(en-US) orCanvasRenderingContext2D.fillText()
(en-US) instead. -
Non-standard
Deprecated
CanvasRenderingContext2D.mozMeasureText()
-
This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0. Use
CanvasRenderingContext2D.measureText()
(en-US) instead. -
Non-standard
Deprecated
CanvasRenderingContext2D.mozPathText()
-
This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
-
Non-standard
Deprecated
CanvasRenderingContext2D.mozTextAlongPath()
-
This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
Internal APIs (chrome-context only)
-
Non-standard
CanvasRenderingContext2D.asyncDrawXULElement()
-
Renders a region of a XUL element into the
canvas
. -
Non-standard
CanvasRenderingContext2D.drawWindow()
(en-US) -
Renders a region of a window into the
canvas
. The contents of the window's viewport are rendered, ignoring viewport clipping and scrolling. -
Non-standard
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
-
Non-standard
CanvasRenderingContext2D.msFillRule
-
The fill rule to use. This must be one of
evenodd
ornonzero
(default).
Especificaciones
Specification |
---|
HTML Standard # 2dcontext |
Browser compatibility
BCD tables only load in the browser