Canvas: Contexto de Renderização em "2D"

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.

A interface Canvas Renderização de Contexto de duas Dimensões ( CanvasRenderingContext2D) é usada para desenhar retangulos, textos, imagens e outros objetos na tag ou elemento canvas. Fornece o contexto de renderização em 2D para a superfície de desenho do elemento <canvas>.

Para obter um objeto desta interface, chama-se getContext() em um elemento <canvas>, adicionando "2d" como argumento, veja o exemplo abaixo:

var canvas = document.getElementById("meuCanvas"); // em seu HTML esse elemento se parece com <canvas id="meuCanvas"></canvas>
var ctx = canvas.getContext("2d");

Agora que você possui o contexto de renderização 2D, você pode desenhar dentro deste canvas. Por exemplo:

ctx.fillStyle = "rgb(200,0,0)"; // define a cor de preenchimento do retângulo
ctx.fillRect(10, 10, 55, 50); // desenha o retângulo na posição 10, 10 com 55 pixels de largura e uma altura de 50

Veja as propriedades e métodos no menu lateral e abaixo. O tutorial canvas tem mais informações, exemplos e recursos.

Desenhando Retângulos

Existem três métodos que imediatamente desenham retângulos ao canvas.

CanvasRenderingContext2D.clearRect(): Determina todos os pixels no retângulo definido, pelo ponto inicial (x, y) e tamanho (largura, altura) para preto transparente, apagando qualquer conteúdo desenhado anteriormente.
CanvasRenderingContext2D.fillRect(): Desenha um retângulo preenchido na posição (x, y) com tamanho definido pela largura e altura
CanvasRenderingContext2D.strokeRect(): Pinta um retângulo o qual possui um ponto inicial em (x, y) e possui um w width(largura) e um h height(altura) dentro da tela(canvas), usando o estilo de traçado(stroke) atual.

Desenhando Textos

Os métodos seguintes são fornecidos para desenhar texto. Veja também o objeto TextMetrics para propriedades de texto.

CanvasRenderingContext2D.fillText(): Desenha(preenche) um texto fornecido, em uma posição fornecida(x,y).
CanvasRenderingContext2D.strokeText(): Desenha(traçados) um texto fornecido, em uma posição fornecida(x,y).
CanvasRenderingContext2D.measureText(): Retorna um objeto TextMetrics .

Estilos de linha

Os seguintes métodos e propriedades, controlam como as linhas são desenhadas.

CanvasRenderingContext2D.lineWidth: Largura das linhas. Padrão: 1.0
CanvasRenderingContext2D.lineCap: Tipos de pontas no final das linhas. Valores possíveis: butt (padrão), round, square.
CanvasRenderingContext2D.lineJoin: Define o tipo de encontro entre duas linhas. Possíveis valores: round, bevel, miter (default).
CanvasRenderingContext2D.miterLimit: Relação do limite de esquadria. Padrão: 10.
CanvasRenderingContext2D.getLineDash(): Retorna a matriz de padrão de traço de linha atual contendo um número par de números não negativos.
CanvasRenderingContext2D.setLineDash(): Define o padrão de traço de linha atual.
CanvasRenderingContext2D.lineDashOffset: Especifica onde iniciar uma matriz de traços em uma linha.

Estilos de textos

As propriedades abaixo controlam a estilização do texto a ser apresentado:

CanvasRenderingContext2D.font: Configuração da fonte. Valor padrão: 10px sans-serif.
CanvasRenderingContext2D.textAlign: Alinhamento do texto. Possíveis valores: start (padrão), end, left, right or center.
CanvasRenderingContext2D.textBaseline: Configuração de alinhamento da linha de base (Baseline). Possíveis valores: top, hanging, middle, alphabetic (padrão), ideographic, bottom.
CanvasRenderingContext2D.direction: Direção do texto. Possívels valores: ltr, rtl, inherit (padrão).

Estilos de preenchimento e traço

O estilo de preenchimento é usado para cores e estilos dentro das formas e o estilo de traço é usado para as linhas ao redor das formas.

CanvasRenderingContext2D.fillStyle: Cor ou estilo para usar formas internas. Padrão #000 (preto).
CanvasRenderingContext2D.strokeStyle: Cor ou estilo a ser usado para as linhas em torno das formas. Padrão: #000 (preto).

Gradientes e padrões

CanvasRenderingContext2D.createLinearGradient(): Cria um gradiente linear ao longo da linha fornecida pelas coordenadas representadas pelos parâmetros.
CanvasRenderingContext2D.createRadialGradient(): Cria um gradiente radial dado pelas coordenadas dos dois círculos representados pelos parâmetros.
CanvasRenderingContext2D.createPattern(): Cria um padrão usando a imagem especificada (uma CanvasImageSource). Ele repete a fonte nas direções especificadas pelo argumento de repetição. Este método retorna um CanvasPattern.

Sombras

CanvasRenderingContext2D.shadowBlur.: Especifica o efeito de desfoque. Padrão: 0.
CanvasRenderingContext2D.shadowColor: Cor da sombra. Padrão: fully-transparent black (preto totalmente transparente).
CanvasRenderingContext2D.shadowOffsetX: Distância horizontal em que a sombra será deslocada. Padrão: 0.
CanvasRenderingContext2D.shadowOffsetY: Distância vertical em que a sombra será deslocada. Padrão: 0.

Caminhos

Os seguintes métodos podem ser usados para manipular caminhos de desenhos.

CanvasRenderingContext2D.beginPath(): Inicia um novo caminho esvaziando a lista de subcaminhos. Chame esse método quando você quiser criar um novo caminho.
CanvasRenderingContext2D.closePath(): Faz com que a ponta da caneta se mova de volta para o início do subcaminho atual. Ele tenta traçar uma linha reta do ponto atual ao início. Se o desenho já foi fechado ou tem apenas um ponto, este método não faz nada.
CanvasRenderingContext2D.moveTo(): Move o ponto inicial de um novo subcaminho para as coordenadas (x, y).
CanvasRenderingContext2D.lineTo(): Conecta o último ponto do caminho atual com as coordenadas (x, y) com linha reta.
CanvasRenderingContext2D.bezierCurveTo(): Adiciona uma curva de Bézier ao caminho atual.
CanvasRenderingContext2D.quadraticCurveTo(): Adiciona uma curva de Bézier quadrática ao caminho atual.
CanvasRenderingContext2D.arc(): Adiciona um arco circular ao caminho atual.
CanvasRenderingContext2D.arcTo(): Adiciona um arco no caminho atual com os pontos de controle e raio fornecidos, conectado ao ponto anterior por uma linha reta.
CanvasRenderingContext2D.ellipse(): Adiciona um arco elíptico ao caminho atual.
CanvasRenderingContext2D.rect(): Cria um caminho de retângulo na posição (x, y) com o tamanho determinado por width e 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.

Transformações

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() Experimental: 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.

Desenhando imagens

CanvasRenderingContext2D.drawImage(): Draws the specified image. This method is available in multiple formats, providing a great deal of flexibility in its use.

Manipulação de pixels

Image smoothing

CanvasRenderingContext2D.imageSmoothingEnabled 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(): 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() 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 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.getContextAttributes(): Inspired by the same WebGLRenderingContext method it returns an Canvas2DContextAttributes 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 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.mozFillRule: The fill rule to use. This must be one of evenodd or nonzero (default).
Non-standard CanvasRenderingContext2D.mozImageSmoothingEnabled: See CanvasRenderingContext2D.imageSmoothingEnabled.
Non-standard Deprecated CanvasRenderingContext2D.mozDash: An array which specifies the lengths of alternating dashes and gaps . Use CanvasRenderingContext2D.getLineDash() and CanvasRenderingContext2D.setLineDash() instead.
Non-standard Deprecated CanvasRenderingContext2D.mozDashOffset: Specifies where to start a dash array on a line. Use CanvasRenderingContext2D.lineDashOffset instead.
Non-standard Deprecated CanvasRenderingContext2D.mozTextStyle: Introduced in in Gecko 1.9, deprecated in favor of the CanvasRenderingContext2D.font property.
Non-standard 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 CanvasRenderingContext2D.mozMeasureText(): This method was introduced in Gecko 1.9 and is unimplemented starting with Gecko 7.0. Use CanvasRenderingContext2D.measureText() instead.
Non-standard CanvasRenderingContext2D.mozPathText(): This method was introduced in Gecko 1.9 and is removed starting with Gecko 7.0.
Non-standard 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(): 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.

Especificações

Specification
HTML Standard # 2dcontext

Compatibilidade com navegadores

BCD tables only load in the browser

Veja também

HTMLCanvasElement