Class OffscreenCanvasRenderingContext2D

Hierarchy

  • OffscreenCanvasRenderingContext2D

Properties

globalAlpha: number

Specifies the alpha (transparency) value that is applied to shapes and images before they are drawn onto the canvas.

Value is between 0.0 (fully transparent) and 1.0 (fully opaque), inclusive. Values outside that range, including Infinity and NaN, will not be set, and globalAlpha will retain its previous value.

globalCompositeOperation: GlobalCompositeOperation

Specifies the type of compositing operation to apply when drawing new shapes.

imageSmoothingEnabled: boolean

Determines whether scaled images are smoothed (true) or not (false).

imageSmoothingQuality: ImageSmoothingQuality

Determines the quality of image smoothing.

Default

"low"

Note

For this property to have an effect, imageSmoothingEnabled must be true.

See

https://developer.mozilla.org/docs/Web/API/CanvasRenderingContext2D/imageSmoothingQuality

lineCap: CanvasLineCap

Determines the shape used to draw the end points of lines.

lineDashOffset: number

Determines the line dash offset (or "phase").

lineJoin: CanvasLineJoin

Determines the shape used to join two line segments where they meet.

This property has no effect wherever two connected segments have the same direction, because no joining area will be added in this case. Degenerate segments with a length of zero (i.e. with all endpoints and control points at the exact same position) are also ignored.

lineWidth: number

Determines the thickness of lines.

miterLimit: number

Specifies the miter limit ratio, in coordinate space units. Zero, negative, Infinity, and NaN values are ignored.

textAlign: CanvasTextAlign

Specifies the current text alignment used when drawing text.

The alignment is relative to the x value of the fillText() / strokeText() methods. For example, if textAlign is "center", then the text's left edge will be at x - (textWidth / 2).

textBaseline: CanvasTextBaseline

Specifies the current text baseline used when drawing text.

Accessors

  • get canvas(): OffscreenCanvas
  • A read-only reference to the OffscreenCanvas object that is associated with the context.

    Returns OffscreenCanvas

  • get fillStyle(): string
  • Specifies the color, gradient, or pattern to use inside shapes.

    Returns string

  • set fillStyle(v): void
  • Parameters

    • v: string

    Returns void

  • get font(): string
  • Specifies the current text style to use when drawing text. This string uses the same syntax as the CSS font specifier.

    Returns string

  • set font(v): void
  • Parameters

    • v: string

    Returns void

  • get strokeStyle(): string
  • Specifies the color, gradient, or pattern to use for the strokes (outlines) around shapes.

    Returns string

  • set strokeStyle(v): void
  • Parameters

    • v: string

    Returns void

Methods

  • Parameters

    • x: number
    • y: number
    • radius: number
    • startAngle: number
    • endAngle: number
    • Optional counterclockwise: boolean

    Returns void

  • Parameters

    • x1: number
    • y1: number
    • x2: number
    • y2: number
    • radius: number

    Returns void

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

    Returns void

    Note

    To create a new sub-path (i.e. one matching the current canvas state), you can use CanvasRenderingContext2D.moveTo().

    See

    https://developer.mozilla.org/docs/Web/API/CanvasRenderingContext2D/beginPath

  • Parameters

    • cp1x: number
    • cp1y: number
    • cp2x: number
    • cp2y: number
    • x: number
    • y: number

    Returns void

  • Erases the pixels in a rectangular area by setting them to transparent black.

    Parameters

    • x: number

      The x-axis coordinate of the rectangle's starting point.

    • y: number

      The y-axis coordinate of the rectangle's starting point.

    • width: number

      The rectangle's width. Positive values are to the right, and negative to the left.

    • height: number

      The rectangle's height. Positive values are down, and negative are up.

    Returns void

  • Attempts to add a straight line from the current point to the start of the current sub-path. If the shape has already been closed or has only one point, this function does nothing.

    This method doesn't draw anything to the canvas directly. You can render the path using the stroke() or fill() methods.

    Returns void

  • Parameters

    • startAngle: number
    • x: number
    • y: number

    Returns CanvasGradient

  • Parameters

    • sw: number
    • sh: number
    • Optional settings: ImageDataSettings

    Returns ImageData

  • Parameters

    Returns ImageData

  • Parameters

    • x0: number
    • y0: number
    • x1: number
    • y1: number

    Returns CanvasGradient

  • Parameters

    Returns null | CanvasPattern

  • Parameters

    • x0: number
    • y0: number
    • r0: number
    • x1: number
    • y1: number
    • r1: number

    Returns CanvasGradient

  • Draws an image onto the canvas.

    Parameters

    • image: CanvasImageSource

      The image to draw onto the canvas.

    • dx: number

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

    • dy: number

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

    Returns void

  • Draws an image onto the canvas.

    Parameters

    • image: CanvasImageSource

      The image to draw onto the canvas.

    • dx: number

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

    • dy: number

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

    • dWidth: number

      The width to draw the image in the destination canvas. This allows scaling of the drawn image.

    • dHeight: number

      The height to draw the image in the destination canvas. This allows scaling of the drawn image.

    Returns void

  • Draws an image onto the canvas.

    Parameters

    • image: CanvasImageSource

      The image to draw onto the canvas.

    • sx: number

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

    • sy: number

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

    • sWidth: number

      The width of the sub-rectangle of the source image to draw into the destination context.

    • sHeight: number

      The height of the sub-rectangle of the source image to draw into the destination context.

    • dx: number

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

    • dy: number

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

    • dWidth: number

      The width to draw the image in the destination canvas. This allows scaling of the drawn image.

    • dHeight: number

      The height to draw the image in the destination canvas. This allows scaling of the drawn image.

    Returns void

  • Parameters

    • x: number
    • y: number
    • radiusX: number
    • radiusY: number
    • rotation: number
    • startAngle: number
    • endAngle: number
    • Optional counterclockwise: boolean

    Returns void

  • Draws a rectangle that is filled according to the current fillStyle.

    This method draws directly to the canvas without modifying the current path, so any subsequent fill() or stroke() calls will have no effect on it.

    Parameters

    • x: number

      The x-axis coordinate of the rectangle's starting point.

    • y: number

      The y-axis coordinate of the rectangle's starting point.

    • width: number

      The rectangle's width. Positive values are to the right, and negative to the left.

    • height: number

      The rectangle's height. Positive values are down, and negative are up.

    Returns void

  • Draws a text string at the specified coordinates, filling the string's characters with the current fillStyle.

    Parameters

    • text: string

      A string specifying the text string to render into the context.

    • x: number

      The x-axis coordinate of the point at which to begin drawing the text, in pixels.

    • y: number

      The y-axis coordinate of the baseline on which to begin drawing the text, in pixels.

    • Optional maxWidth: number

      The maximum number of pixels wide the text may be once rendered. If not specified, there is no limit to the width of the text.

    Returns void

  • Returns an ImageData object representing the underlying pixel data for a specified portion of the canvas.

    This method is not affected by the canvas's transformation matrix. If the specified rectangle extends outside the bounds of the canvas, the pixels outside the canvas are transparent black in the returned ImageData object.

    Parameters

    • sx: number

      The x-axis coordinate of the top-left corner of the rectangle from which the ImageData will be extracted.

    • sy: number

      The y-axis coordinate of the top-left corner of the rectangle from which the ImageData will be extracted.

    • sw: number

      The width of the rectangle from which the ImageData will be extracted. Positive values are to the right, and negative to the left.

    • sh: number

      The height of the rectangle from which the ImageData will be extracted. Positive values are down, and negative are up.

    • Optional settings: ImageDataSettings

    Returns ImageData

    An ImageData object containing the image data for the rectangle of the canvas specified.

  • Gets the current line dash pattern.

    Returns number[]

    An Array of numbers that specify distances to alternately draw a line and a gap (in coordinate space units). If the number, when setting the elements, is odd, the elements of the array get copied and concatenated. For example, setting the line dash to [5, 15, 25] will result in getting back [5, 15, 25, 5, 15, 25].

  • Parameters

    • x: number
    • y: number

    Returns void

  • Parameters

    • x: number
    • y: number

    Returns void

  • Parameters

    Returns void

  • Parameters

    • cpx: number
    • cpy: number
    • x: number
    • y: number

    Returns void

  • Parameters

    • x: number
    • y: number
    • w: number
    • h: number

    Returns void

  • Adds the specified angle of rotation to the transformation matrix.

    Parameters

    • angle: number

      The rotation angle, clockwise in radians. You can use degree * Math.PI / 180 to calculate a radian from a degree.

    Returns void

  • Adds a rounded rectangle to the current path.

    Parameters

    • x: number

      The x-axis coordinate of the rectangle's starting point, in pixels.

    • y: number

      The y-axis coordinate of the rectangle's starting point, in pixels.

    • width: number

      The rectangle's width. Positive values are to the right, and negative to the left.

    • height: number

      The rectangle's height. Positive values are down, and negative are up.

    • radii: number | DOMPointInit | Iterable<number | DOMPointInit> = 0

      A number or list specifying the radii of the circular arc to be used for the corners of the rectangle.

    Returns void

  • Adds a scaling transformation to the canvas units horizontally and/or vertically.

    By default, one unit on the canvas is exactly one pixel. A scaling transformation modifies this behavior. For instance, a scaling factor of 0.5 results in a unit size of 0.5 pixels; shapes are thus drawn at half the normal size. Similarly, a scaling factor of 2.0 increases the unit size so that one unit becomes two pixels; shapes are thus drawn at twice the normal size.

    Parameters

    • x: number

      Scaling factor in the horizontal direction. A negative value flips pixels across the vertical axis. A value of 1 results in no horizontal scaling.

    • y: number

      Scaling factor in the vertical direction. A negative value flips pixels across the horizontal axis. A value of 1 results in no vertical scaling.

    Returns void

  • Sets the line dash pattern used when stroking lines. It uses an array of values that specify alternating lengths of lines and gaps which describe the pattern.

    Parameters

    • segments: number[]

      An Array of numbers that specify distances to alternately draw a line and a gap (in coordinate space units). If the number of elements in the array is odd, the elements of the array get copied and concatenated. For example, [5, 15, 25] will become [5, 15, 25, 5, 15, 25]. If the array is empty, the line dash list is cleared and line strokes return to being solid.

    Returns void

    Note

    To return to using solid lines, set the line dash list to an empty array.

    See

    https://developer.mozilla.org/docs/Web/API/CanvasRenderingContext2D/setLineDash

  • Draws a rectangle that is stroked (outlined) according to the current strokeStyle and other context settings.

    This method draws directly to the canvas without modifying the current path, so any subsequent fill() or stroke() calls will have no effect on it.

    Parameters

    • x: number

      The x-axis coordinate of the rectangle's starting point.

    • y: number

      The y-axis coordinate of the rectangle's starting point.

    • width: number

      The rectangle's width. Positive values are to the right, and negative to the left.

    • height: number

      The rectangle's height. Positive values are down, and negative are up.

    Returns void

  • Draws the outlines of the characters of the text string at the specified coordinates, stroking the string's characters with the current strokeStyle.

    Parameters

    • text: string

      A string specifying the text string to render into the context.

    • x: number

      The x-axis coordinate of the point at which to begin drawing the text, in pixels.

    • y: number

      The y-axis coordinate of the baseline on which to begin drawing the text, in pixels.

    • Optional maxWidth: number

      The maximum number of pixels wide the text may be once rendered. If not specified, there is no limit to the width of the text.

    Returns void

  • Multiplies the current transformation with the matrix described by the arguments of this method. This lets you scale, rotate, translate (move), and skew the context.

    Parameters

    • a: number

      (m11) The cell in the first row and first column of the matrix.

    • b: number

      (m12) The cell in the second row and first column of the matrix.

    • c: number

      (m21) The cell in the first row and second column of the matrix.

    • d: number

      (m22) The cell in the second row and second column of the matrix.

    • e: number

      (m41) The cell in the first row and third column of the matrix.

    • f: number

      (m42) The cell in the second row and third column of the matrix.

    Returns void

  • Adds a translation transformation to the current matrix by moving the canvas and its origin x units horizontally and y units vertically on the grid.

    Parameters

    • x: number

      Distance to move in the horizontal direction. Positive values are to the right, and negative to the left.

    • y: number

      Distance to move in the vertical direction. Positive values are down, and negative are up.

    Returns void

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