CanvasRenderingContext2D

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

L'interface CanvasRenderingContext2D est utilisée pour dessiner des rectangles, du texte, des images et d'autres objets sur l'élément canvas. Il fournit le contexte de rendu 2D pour la surface de dessin d'un élément <canvas>.

Pour obtenir un objet de cette interface, appelez getContext() sur un élément <canvas>, en fournissant "2d" comme argument :

var canevas = document.getElementById("tutorial"); // dans votre HTML, cet élément apparaît comme <canvas id="monCanevas"></canvas>
var ctx = canevas.getContext("2d");

Une fois que vous avez le contexte de rendu 2D pour un canevas, vous pouvez dessiner à l'intérieur. Par exemple :

ctx.fillStyle = "rgb(200,0,0)"; // définit la couleur de remplissage du rectangle
ctx.fillRect(10, 10, 55, 50); // dessine le rectangle à la position 10, 10 d'une largeur de 55 et d'une hauteur de 50

Voir les propriétés et les méthodes dans la barre latérale et plus bas. Le tutoriel canvas a davantage d'informations, d'exemples et de ressources également.

Dessin de rectangles

Il existe trois méthodes qui dessinent immédiatement des rectangles sur la bitmap.

CanvasRenderingContext2D.clearRect(): Initialise tous les pixels dans le rectangle défini par le point de départ (x, y) et la taille (largeur, hauteur) à noir transparent, en effaçant tout contenu précédemment dessiné.
CanvasRenderingContext2D.fillRect(): Dessine un rectangle rempli à la position (x, y) dont la taille est déterminée par largeur et hauteur.
CanvasRenderingContext2D.strokeRect(): Peint un rectangle ayant un point de départ en (x, y), une largeur l et une hauteur h sur le canevas, en utilisant le style de trait en cours.

Dessiner du texte

Les méthodes suivantes permettent de dessiner du texte. Voir aussi l'objet TextMetrics pour les propriétés du texte.

CanvasRenderingContext2D.fillText(): Dessine (rempli) un texte donné à la position (x,y) donnée.
CanvasRenderingContext2D.strokeText(): Dessine (contour) un texte donné à la position (x, y) donnée.
CanvasRenderingContext2D.measureText(): Renvoie un objet TextMetrics.

Styles de ligne

Les méthodes et propriétés suivantes controllent comment les lignes sont dessinées.

CanvasRenderingContext2D.lineWidth: Largeur des lignes. Défaut 1.0
CanvasRenderingContext2D.lineCap: Type de finission pour la fin de la ligne. Valeurs possible: butt (défaut), round, square.
CanvasRenderingContext2D.lineJoin: Définit le type de coin quand deux lignes se rejoignent. Valeurs possible: round, bevel, miter (défaut).
CanvasRenderingContext2D.miterLimit: Le taux limite du miter. Sa valeur par défaut est 10.
CanvasRenderingContext2D.getLineDash(): Retourne le tableau de modèle du trait courant contenant un nombre pair de nombre positifs.
CanvasRenderingContext2D.setLineDash(): Définit le modèle du trait courant.
CanvasRenderingContext2D.lineDashOffset: Specifies where to start a dash array on a line.

Styles de texte

Les propriétés suivantes contrôlent la manière dont le texte est rendu à l'affichage.

CanvasRenderingContext2D.font: Paramètre de fonte dont la valeur par défaut est 10px sans-serif.
CanvasRenderingContext2D.textAlign: Paramètre d'alignement horizontal. Ses valeurs possibles sont : start (par défaut), end, left, right et center.
CanvasRenderingContext2D.textBaseline: Paramètre d'alignement vertical par rapport à la ligne de base du texte. Ses valeurs possibles sont : top, hanging, middle, alphabetic (par défaut), ideographic, bottom.
CanvasRenderingContext2D.direction: Direction d'affichage. Ses valeurs possibles sont : ltr, rtl, inherit (par défaut).

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 a CanvasPattern.

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() Expérimental: 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.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() Expérimental: 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

Image smoothing

CanvasRenderingContext2D.imageSmoothingEnabled Expérimental: 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 be null if it is not associated with a <canvas> element.

Hit regions

CanvasRenderingContext2D.addHitRegion() Expérimental: Adds a hit region to the canvas.
CanvasRenderingContext2D.removeHitRegion() Expérimental: Removes the hit region with the specified id from the canvas.
CanvasRenderingContext2D.clearHitRegions() Expérimental: 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 and CanvasRenderingContext2D.shadowBlur.
Non standard CanvasRenderingContext2D.drawImageFromRect(): This is redundant with an equivalent overload of drawImage.
Non standard CanvasRenderingContext2D.setAlpha(): Use CanvasRenderingContext2D.globalAlpha instead.
Non standard CanvasRenderingContext2D.setCompositeOperation(): Use CanvasRenderingContext2D.globalCompositeOperation instead.
Non standard CanvasRenderingContext2D.setLineWidth(): Use CanvasRenderingContext2D.lineWidth instead.
Non standard CanvasRenderingContext2D.setLineJoin(): Use CanvasRenderingContext2D.lineJoin instead.
Non standard CanvasRenderingContext2D.setLineCap(): Use CanvasRenderingContext2D.lineCap instead.
Non standard CanvasRenderingContext2D.setMiterLimit(): Use CanvasRenderingContext2D.miterLimit instead.
Non standard CanvasRenderingContext2D.setStrokeColor(): Use CanvasRenderingContext2D.strokeStyle instead.
Non standard CanvasRenderingContext2D.setFillColor(): Use CanvasRenderingContext2D.fillStyle instead.
Non standard CanvasRenderingContext2D.setShadow(): Use CanvasRenderingContext2D.shadowColor and CanvasRenderingContext2D.shadowBlur instead.
Non standard CanvasRenderingContext2D.webkitLineDash: Use CanvasRenderingContext2D.getLineDash() and CanvasRenderingContext2D.setLineDash() instead.
Non standard CanvasRenderingContext2D.webkitLineDashOffset: Use CanvasRenderingContext2D.lineDashOffset instead.
Non standard CanvasRenderingContext2D.webkitImageSmoothingEnabled: Use CanvasRenderingContext2D.imageSmoothingEnabled instead.

Blink only

Non standard CanvasRenderingContext2D.isContextLost(): Inspired by the same WebGLRenderingContext method it returns true if the Canvas context has been lost, or false 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: CSS and SVG filters as Canvas APIs. Likely to be standardized in a new version of the specification.

Prefixed APIs

Non standard CanvasRenderingContext2D.mozImageSmoothingEnabled: See CanvasRenderingContext2D.imageSmoothingEnabled.
Non standard Obsolète CanvasRenderingContext2D.mozTextStyle: Introduced in in Gecko 1.9, deprecated in favor of the CanvasRenderingContext2D.font property.
Non standard Obsolète CanvasRenderingContext2D.mozDrawText(): This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0. Use CanvasRenderingContext2D.strokeText() or CanvasRenderingContext2D.fillText() instead.
Non standard Obsolète CanvasRenderingContext2D.mozMeasureText(): This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0. Use CanvasRenderingContext2D.measureText() instead.
Non standard Obsolète CanvasRenderingContext2D.mozPathText(): This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
Non standard Obsolète 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.drawWindow(): 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 or nonzero (default).

Spécifications

Specification
HTML Standard # 2dcontext

Compatibilité des navigateurs

BCD tables only load in the browser

Voir aussi

HTMLCanvasElement