CanvasRenderingContext2D

Le contexte de rendu 2D pour la surface de dessin d'un élément <canvas>. Pour obtenir cet objet, appelez getContext () sur un <canvas>, en fournissant "2d" comme argument:

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

Une fois que vous avez votre contexte de rendu 2D pour un canvas, vous pouvez dessiner dedans. Par exemple:

ctx.fillStyle = "rgb(200,0,0)";  
ctx.fillRect(10, 10, 55, 50);  

Voir le tutoriel à propos des Canvas pour plus d'informations, d'exemples et de ressources.

Method overview

Gecko-specific Method overview

WebKit-specific Method overview

Attributes

Gecko-specific attributes

WebKit-specific attributes

Constants

Gecko-specific constants/flags

Methods

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).

void arc(
  in float x,
  in float y,
  in float radius,
  in float startAngle,
  in float endAngle,
  in boolean anticlockwise [optional]
);

Parameters

x

The x axis of the coordinate for the arc's center

y

The y axis of the coordinate for the arc's center.

radius

The arc's radius

startAngle

The starting point, measured from the x axis, from which it will be drawn, expressed in radians.

endAngle

The end arc's angle to which it will be drawn, expressed in radians.

anticlockwise Facultatif depuis Gecko 2.0

true draws the arc anticlockwise (AKA counter-clockwise), otherwise in a clockwise direction.

arcTo()

Adds an arc to the path with the given control points and radius, connected to the previous point by a straight line.

void arcTo(
  in float x1,
  in float y1,
  in float x2,
  in float y2,
  in float radius
);

Parameters

x1

The x axis of the coordinate for the first control point.

y1

The y axis of the coordinate for the first control point.

x2

The x axis of the coordinate for the second control point.

y2

The y axis of the coordinate for the second control point.

radius

The arc's radius.

beginPath()

Starts a new path by resetting the list of sub-paths. Call this method when you want to create a new path.

void beginPath();

Parameters

None.

bezierCurveTo()

void bezierCurveTo(
  in float cp1x,
  in float cp1y,
  in float cp2x,
  in float cp2y,
  in float x,
  in float y
);

Parameters

cp1x

 

cp1y

 

cp2x

 

cp2y

 

x

 

y

 

clearRect()

Sets all pixels in the rectangle defined by starting point (x, y) and size (width, height) to transparent black.

void clearRect(
  in float x,
  in float y,
  in float width,
  in float height
);

Parameters

x

The x axis of the coordinate for the rectangle starting point.

y

The y axis of the coordinate for the rectangle starting point.

width

The rectangle's width.

height

The rectangle's height.

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.

void clip();

Parameters

None.

closePath()

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.

void closePath();

Parameters

None.

createImageData()

Creates a new, blank ImageData object with the specified dimensions. All of the pixels in the new object are transparent black.

ImageData createImageData(
  in float width,
  in float height
);
ImageData createImageData(
  ImageData imagedata
);

Parameters

width

The width to give the new ImageData object.

height

The height to give the new ImageData object.

imagedata

An existing ImageData object from which to copy the width and height. The image itself is not copied.

Return value

A new ImageData object with the specified width and height. The new object is filled with transparent black pixels.

createLinearGradient()

Creates a gradient along the line given by the coordinates represented by the parameters.

nsIDOMCanvasGradient createLinearGradient(
  in float x0,
  in float y0,
  in float x1,
  in float y1
);

Parameters

x0

The x axis of the coordinate of the start point.

y0

The y axis of the coordinate of the start point.

x1

The x axis of the coordinate of the end point.

y1

The y axis of the coordinate of the end point.

Return value

nsIDOMCanvasGradient

createPattern()

nsIDOMCanvasPattern createPattern(
  in nsIDOMHTMLElement image,
  in DOMString repetition
);

Parameters

image

A DOM element to use as the source image for the pattern. This can be any element, although typically you'll use an Image or <canvas>.

repetition

A string representing the direction of repetition.

Possible values:

• repeat
• repeat-x
• repeat-y
• no-repeat

Return value

A new DOM canvas pattern object for use in pattern-based operations.

Exceptions thrown

NS_ERROR_DOM_INVALID_STATE_ERR

The specified <canvas> element for the image parameter is zero-sized (that is, one or both of its dimensions are 0 pixels).

createRadialGradient()

nsIDOMCanvasGradient createRadialGradient(
  in float x0,
  in float y0,
  in float r0,
  in float x1,
  in float y1,
  in float r1
);

Parameters

x0

 

y0

 

r0

 

x1

 

y1

 

r1

 

Return value

nsIDOMCanvasGradient

drawCustomFocusRing()

boolean drawCustomFocusRing(Element element);

Parameters

element

 

Return value

boolean

drawImage()

Draws the specified image. This method is available in multiple formats, providing a great deal of flexibility in its use.

void drawImage(
  in nsIDOMElement image,
  in float dx,
  in float dy
);

void drawImage(
  in nsIDOMElement image,
  in float dx,
  in float dy,
  in float dw,
  in float dh
);

void drawImage(
  in nsIDOMElement image,
  in float sx,
  in float sy,
  in float sw,
  in float sh,
  in float dx, 
  in float dy,
  in float dw,
  in float dh
);

Parameters

image

An element to draw into the context; the specification permits any image element (that is, <img>, <canvas>, and <video>). Some browsers let you use any arbitrary element; Firefox doesn’t.

dx

The X coordinate in the destination canvas at which to place the top-left corner of the source image.

dy

The Y coordinate in the destination canvas at which to place the top-left corner of the source image.

dw

The width to draw the image in the destination canvas. This allows scaling of the drawn image. If not specified, the image is not scaled in width when drawn.

dh

The height to draw the image in the destination canvas. This allows scaling of the drawn image. If not specified, the image is not scaled in height when drawn.

sx

The X coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context.

sy

The Y coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context.

sw

The width of the sub-rectangle of the source image to draw into the destination context. If not specified, the entire rectangle from the coordinates specified by sx and sy to the bottom-right corner of the image is used. If you specify a negative value, the image is flipped horizontally when drawn.

sh

The height of the sub-rectangle of the source image to draw into the destination context. If you specify a negative value, the image is flipped vertically when drawn.

The diagram below illustrates the meanings of the various parameters.

Exceptions thrown

INDEX_SIZE_ERR

If the canvas or source rectangle width or height is zero.

INVALID_STATE_ERR

The image has no image data.

TYPE_MISMATCH_ERR

The specified source element isn't supported. This is not thrown by Firefox, since any element may be used as a source image.

Compatibility notes

• Prior to Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), Firefox threw an exception if any of the coordinate values was non-finite or zero. As per the specification, this no longer happens.
• Support for flipping the image by using negative values for sw and sh was added in Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2).
• Gecko 9.0 (Firefox 9.0 / Thunderbird 9.0 / SeaMonkey 2.6) now correctly supports CORS for drawing images across domains without tainting the canvas.
• Gecko 11.0 (Firefox 11.0 / Thunderbird 11.0 / SeaMonkey 2.8) now allows SVG-as-an-image to be drawn into a canvas without tainting the canvas.

drawSystemFocusRing()

void drawSystemFocusRing(Element element);

Parameters

element

 

fill()

Fills the subpaths with the current fill style.

void fill();

Parameters

None.

fillRect()

Draws a filled rectangle at (x, y) position whose size is determined by width and height.

void fillRect(
  in float x,
  in float y,
  in float width,
  in float height
);

Parameters

x

The x axis of the coordinate for the rectangle starting point.

y

The y axis of the coordinate for the rectangle starting point.

width

The rectangle's width.

height

The rectangle's height.

fillText()

void fillText(
  in DOMString text,
  in float x,
  in float y,
  in float maxWidth [optional]
);

Parameters

text

 

x

 

y

 

maxWidth Facultatif

 

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.

ImageData getImageData(   
  in double sx, 
  in double sy, 
  in double sw, 
  in double sh
);

Parameters

sx

The x axis of the coordinate for the rectangle startpoint from which the ImageData will be extracted.

sy

The x axis of the coordinate for the rectangle endpoint from which the ImageData will be extracted.

sw

The width of the rectangle from which the ImageData will be extracted.

sh

The height of the rectangle from which the ImageData will be extracted.

Return value

Returns an ImageData object containing the image data for the given rectangle of the canvas.

getLineDash()

Returns a dash list array containing an even number of non-negative numbers.

sequence getLineDash(   
);

Parameters

None.

Return value

Returns a dash list array containing an even number of non-negative numbers.

isPointInPath()

Reports whether or not the specified point is contained in the current path.

boolean isPointInPath(
  in float x,
  in float y
);

Parameters

x

The X coordinate of the point to check.

y

The Y coordinate of the point to check.

Return value

true if the specified point is contained in the current path, otherwise false.

Compatibility notes

• Prior to Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), this method incorrectly failed to multiply the specified point's coordinates by the current transformation matrix before comparing it to the path. Now this method works correctly even if the context is rotated, scaled, or otherwise transformed.

isPointInStroke()

Reports whether or not the specified point is inside the area contained by the stroking of a path.

boolean isPointInStroke(
  in float x,
  in float y
);

Parameters

x

The X coordinate of the point to check.

y

The Y coordinate of the point to check.

Return value

true if the point is inside the area contained by the stroking of a path, otherwise false.

lineTo()

Connects the last point in the subpath to the x, y coordinates with a straight line.

void lineTo(
  in float x,
  in float y
);

Parameters

x

The x axis of the coordinate for the end of the line.

y

The y axis of the coordinate for the end of the line.

measureText()

nsIDOMTextMetrics measureText(
  in DOMString text
);

Parameters

text

 

Return value

nsIDOMTextMetrics (see whatwg spec)

moveTo()

Moves the starting point of a new subpath to the (x, y) coordinates.

void moveTo(
  in float x,
  in float y
);

Parameters

x

The x axis of the point.

y

The y axis of the point.

putImageData()

void putImageData(
  in ImageData imagedata,
  in long dx,
  in long dy,
  in long dirtyX, [optional]
  in long dirtyY, [optional]
  in long dirtyWidth, [optional]
  in long dirtyHeight [optional]
);

Parameters

imageData

     An imageData object containing the array of pixel values.

dx

Position offset in the target canvas context of the rectangle to be painted, relative to the rectangle in the origin image data.

dy

Position offset in the target canvas context of the rectangle to be painted, relative to the rectangle in the origin image data.

dirtyX Facultatif

Position of the top left point of the rectangle to be painted, in the origin image data. Defaults to the top left of the whole image data.

dirtyY Facultatif

Position of the top left point of the rectangle to be painted, in the origin image data. Defaults to the top left of the whole image data.

dirtyWidth Facultatif

Width of the rectangle to be painted, in the origin image data. Defaults to the width of the image data.

dirtyHeight Facultatif

Height of the rectangle to be painted, in the origin image data. Defaults to the height of the image data.

To understand what this algorithm performs, here is an implementation on top of fillRect().

function putImageData(ctx, imageData, dx, dy,
    dirtyX, dirtyY, dirtyWidth, dirtyHeight) {
  var data = imageData.data;
  var height = imageData.height;
  var width = imageData.width;
  dirtyX = dirtyX || 0;
  dirtyY = dirtyY || 0;
  dirtyWidth = dirtyWidth !== undefined? dirtyWidth: width;
  dirtyHeight = dirtyHeight !== undefined? dirtyHeight: height;
  var limitBottom = dirtyY + dirtyHeight;
  var limitRight = dirtyX + dirtyWidth;
  for (var y = dirtyY; y < limitBottom; y++) {
    for (var x = dirtyX; x < limitRight; x++) {
      var pos = y * width + x;
      ctx.fillStyle = 'rgba(' + data[pos*4+0]
                        + ',' + data[pos*4+1]
                        + ',' + data[pos*4+2]
                        + ',' + (data[pos*4+3]/255) + ')';
      ctx.fillRect(x + dx, y + dy, 1, 1);
    }
  }
}

Compatibility notes

• Starting in Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0 / SeaMonkey 2.7), non-finite values to any of these parameters cause the call to putImageData() to be silently ignored, rather than throwing an exception.

quadraticCurveTo()

void quadraticCurveTo(
  in float cpx,
  in float cpy,
  in float x,
  in float y
);

Parameters

cpx

 

cpy

 

x

 

y

 

rect()

void rect(
  in float x,
  in float y,
  in float w,
  in float h
);

Parameters

x

 

y

 

w

 

h

 

restore()

Restores the drawing style state to the last element on the 'state stack' saved by save().

void restore();

Parameters

None.

rotate()

void rotate(
  in float angle
);

Parameters

angle

 

save()

Saves the current drawing style state using a stack so you can revert any change you make to it using restore().

void save();

Parameters

None.

scale()

void scale(
  in float x,
  in float y
);

Parameters

x

 

y

 

scrollPathIntoView()

void scrollPathIntoView();

Parameters

None.

setLineDash()

void setLineDash(
  sequence segments
);

Parameters

segments

An even number of non-negative numbers specifying a dash list.

setTransform()

void setTransform(
  in float m11,
  in float m12,
  in float m21,
  in float m22,
  in float dx,
  in float dy
);

Parameters

m11

 

m12

 

m21

 

m22

 

dx

 

dy

 

stroke()

Strokes the subpaths with the current stroke style.

void stroke();

Parameters

None.

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.

void strokeRect(
  in float x,
  in float y,
  in float w,
  in float h
);

Parameters

x

The x axis for the starting point of the rectangle.

y

The y axis for the starting point of the rectangle.

w

The rectangle's width.

h

The rectangle's height.

strokeText()

void strokeText(
  in DOMString text,
  in float x,
  in float y,
  in float maxWidth [optional]
);

Parameters

text

 

x

 

y

 

maxWidth Facultatif

 

transform()

void transform(
  in float m11,
  in float m12,
  in float m21,
  in float m22,
  in float dx,
  in float dy
);

Parameters

m11

 

m12

 

m21

 

m22

 

dx

 

dy

 

translate()

Moves the origin point of the context to (x, y).

void translate(
  in float x,
  in float y
);

Parameters

x

The x axis for the point to be considered as the origin.

y

The y axis for the point to be considered as the origin.

Gecko-specific methods

void asyncDrawXULElement(
  in nsIDOMXULElement elem,
  in float x,
  in float y,
  in float w,
  in float h,
  in DOMString bgColor,
  in unsigned long flags [optional]
);

Parameters

elem

 

x

 

y

 

w

 

h

 

bgColor

 

flags Facultatif

 

drawWindow()

This API cannot currently be used by Web content. It is chrome only.

Renders a region of a window into the canvas. The contents of the window's viewport are rendered, ignoring viewport clipping and scrolling.

Of course, the rendering obeys the current scale(), transform(), and globalAlpha values.

Hints: If 'rgba(0,0,0,0)' is used for the background color, the drawing will be transparent wherever the window is transparent. Top-level browsed documents are usually not transparent because the user's background-color preference is applied, but IFRAMEs are transparent if the page doesn't set a background. If an opaque color is used for the background color, rendering will be faster because we won't have to compute the window's transparency.

void drawWindow(
  in nsIDOMWindow window,
  in float x,
  in float y,
  in float w,
  in float h,
  in DOMString bgColor,
  in unsigned long flags [optional]
);

Parameters

window

 

x

 

y

 

w

 

h

Specify the area of the window to render, in CSS pixels.

bgColor

The canvas is filled with this color before we render the window into it. This color may be transparent/translucent. It is given as a CSS color string (for example, rgb() or rgba()).

flags Facultatif

Used to better control the drawWindow call. Flags can be ORed together. See the section on Gecko-specific constants above.

Introduced in Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1).

void getFillStyle_multi(
  out DOMString str,
  out nsISupports iface,
  out long type
);

Parameters

str

 

iface

 

type

 

Introduced in Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1).

void getImageData_explicit(
  in long x,
  in long y,
  in unsigned long width,
  in unsigned long height,
  [array, size_is(dataLen)] in octet dataPtr,
  in unsigned long dataLen
);

Parameters

x

 

y

 

width

 

height

 

dataPtr

 

dataLen

 

Introduced in Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1).

void getStrokeStyle_multi(
  out DOMString str,
  out nsISupports iface,
  out long type
);

Parameters

str

 

iface

 

type

 

This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0.

void mozDrawText(
  in DOMString textToDraw
);

Parameters

textToDraw

 

This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0.

float mozMeasureText(
  in DOMString textToMeasure
);

Parameters

textToMeasure

 

Return value

This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0.

void mozPathText(
  in DOMString textToPath
);

Parameters

textToPath

 

This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0.

void mozTextAlongPath(
  in DOMString textToDraw,
  in boolean stroke
);

Parameters

textToDraw

 

stroke

 

Introduced in Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1).

void setFillStyle_multi(
  in DOMString str,
  in nsISupports iface
);

Parameters

str

 

iface

 

Introduced in Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1).

void setStrokeStyle_multi(
  in DOMString str,
  in nsISupports iface
);

Parameters

str

 

iface

 

WebKit-specific methods

clearShadow()

void clearShadow();

Parameters

None.

drawImageFromRect()

void drawImageFromRect(
  in HTMLImageElement image,
  in [Optional] float sx,
  in [Optional] float sy,
  in [Optional] float sw,
  in [Optional] float sh,
  in [Optional] float dx, 
  in [Optional] float dy,
  in [Optional] float dw,
  in [Optional] float dh,
  in [Optional] DOMString compositeOperation
);

setAlpha()

void setAlpha(
  in float alpha
);

setCompositeOperation()

void setCompositeOperation(
  in DOMString compositeOperation
);

setLineWidth()

void setLineWidth(
  in float width
);

setLineCap()

void setLineCap(
  in DOMString cap
);

setLineJoin()

void setLineJoin(
  in DOMString join
);

setMiterLimit()

void setMiterLimit(
  in float limit
);

setStrokeColor()

void setStrokeColor(in DOMString color, in [Optional] float alpha);
void setStrokeColor(in float grayLevel, in [Optional] float alpha);
void setStrokeColor(in float r, in float g, in float b, in float a);
void setStrokeColor(in float c, in float m, in float y, in float k, in float a);

setFillColor()

void setFillColor(in DOMString color, in [Optional] float alpha);
void setFillColor(in float grayLevel, in [Optional] float alpha);
void setFillColor(in float r, in float g, in float b, in float a);
void setFillColor(in float c, in float m, in float y, in float k, in float a);

setShadow()

void setShadow(in float width, in float height, in float blur, in [Optional] DOMString color, in [Optional] float alpha);
void setShadow(in float width, in float height, in float blur, in float grayLevel, in [Optional] float alpha);
void setShadow(in float width, in float height, in float blur, in float r, in float g, in float b, in float a);
void setShadow(in float width, in float height, in float blur, in float c, in float m, in float y, in float k, in float a);

Browser compatibility

Notes

Gecko

Specification

• https://www.whatwg.org/specs/web-apps...eringcontext2d