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Readback, Copy and Blit

luma.gl offers a set of functions that copy or blit data from and to Texture and Framebuffer objects. Image data can also be copied into Buffer, TypedArray, Images or Urls.

Readback Functions

readPixelsToArray(source : Framebuffer|Texture [, options: Object]) : TypedArray

Reads data from a Framebuffer or Texture object into a TypedArray object and returns it. A new TypedArray object is created when not provided. This method requires a sync between CPU and GPU as pixel values are copied from GPU texture memory to CPU Array object memory. This could introduce a delay as it waits for GPU to finish updating the texture. For asynchronous read, check copyToBuffer method.

  • source (Texture or Framebuffer) - This object will be bound and data copied from it.

Optional parameters:

  • options.sourceX - (number, default: 0) X offset of the area to be copied,
  • options.sourceY - (number, default: 0) Y offset of the area to be copied,
  • options.sourceFormat - (GLenum, default: GL.RGBA) The format of the data.
  • options.sourceAttachment - (GLenum, default: COLOR_ATTACHMENT0) Used to deduce the type when not provided.
  • options.target - (TypedArray, default: null) Array object, into which data to be copied, new object is created when not provided.
  • options.sourceWidth - (number, default: source width) The width of the area to be copied.
  • options.sourceHeight - (number, default: source height) The height of the area to be copied.
  • options.sourceType - (GLenum, default: type of pixelArray or UNSIGNED_BYTE) The type of the data.

Notes:

  • Reading from floating point textures is dependent on an extension both in WebGL1 and WebGL2.
  • When supported, the {format: GL.RGBA, type: GL.FLOAT, ...} combination becomes valid for reading from a floating-point color buffer.
  • When color attachment is a float texture with format less than 4 channels, i.e, GL.R32F, or GL.RG32F, readPixels should still be called with a 4 component format(GL.RGBA), and default value (R:0, G:0, B: 0 and A: 1) will be returned for un-used channel.

This function makes calls to the following WebGL APIs:

gl.readPixels, gl.bindFramebuffer

readPixelsToBuffer(source : Framebuffer|Texture, options: Object) : Buffer (WebGL2)

Reads data from a Framebuffer or Texture object into A Buffer object and returns it. A new Buffer object is created when not provided. This method avoids a sync between CPU and GPU as pixel values are copied from GPU texture memory to GPU Buffer memory. This method returns right away without any delays.

A CPU and GPU sync will be triggered when the returned buffer data is read using buffer.getData(), but applications can delay this read, which can reduces the delay due to the sync, or the sync can be completely avoided by using the Buffer as the source of input to the GPU (either as ARRAY_BUFFER or PIXEL_UNPACK_BUFFER).

  • source (Texture or Framebuffer) - This object will be bound and data copied from it.

Optional parameters:

  • options.sourceX - (number, default: 0) X offset of the area to be copied,
  • options.sourceY - (number, default: 0) Y offset of the area to be copied,
  • options.sourceFormat - (GLenum, default: GL.RGBA) The format of the data.
  • options.target - (Buffer) Buffer object, into which data to be copied, new object is created when not provided.
  • options.targetByteOffset - (number, default: 0) Byte offset from which data should be copied into buffer.
  • options.sourceWidth - (number, default: source.width) The width of the area to be copied,
  • options.sourceHeight - (number, default: source.height) The height of the area to be copied,
  • options.sourceType - (GLenum, default: type of target or UNSIGNED_BYTE) The type of the data.

Notes:

  • Reading from floating point textures is dependent on an extension both in WebGL1 and WebGL2.
  • When supported, the {format: GL.RGBA, type: GL.FLOAT, ...} combination becomes valid for reading from a floating-point color buffer.

This function makes calls to the following WebGL APIs:

gl.readPixels, gl.bindFramebuffer, gl.bindBuffer

Copy Functions

copyToDataUrl(source : Framebuffer|Texture, options: Object) : Data URL

Reads data form a Texture or Framebuffer object and returns a Data URL containing the pixel data in PNG format.

  • source (Texture or Framebuffer) - This object will be bound and data copied from it.

Optional parameters:

  • options.sourceAttachment - (GLenum, default: COLOR_ATTACHMENT0) Used to deduce the type when not provided.
  • options.targetMaxHeight - (number, default: Number.MAXSAFEINTEGER) Maximum height of the image to be in returned Data URL.

Note:

  • Works only under a browser environment, doesn't work under Node.

This function makes calls to the following WebGL APIs:

gl.readPixels, gl.bindFramebuffer

copyToImage(source : Framebuffer|Texture, options: Object) : Image

Reads data form a Texture or Framebuffer object and copies it to provided image, new Image instance is created if not provided.

  • source (Texture or Framebuffer) - This object will be bound and data copied from it.

Optional parameters:

  • options.sourceAttachment - (GLenum, default: COLOR_ATTACHMENT0) Used to deduce the type when not provided.
  • options.targetImage - (Image, Optional) Image to to which pixel data to be copied, new one is created if not provide.

Note:

  • Works only under a browser environment, doesn't work under Node.

This function makes calls to the following WebGL APIs:

gl.readPixels, gl.bindFramebuffer

copyToTexture(source : Framebuffer|Texture, target: Texture|GL-enum, options: Object) : Texture

Copies pixels from a Framebuffer or Texture object into the specified area of a two-dimensional texture image or cube-map texture image. (gl.copyTexImage2D, gl.copyTexSubImage2D and gl.copyTexSubImage3D wrapper)

  • source (Texture or Framebuffer) - If provided this object will be bound and data copied from it.
  • target (Texture or GL enum) - Texture object or GL enum specifying the target binding point, to which data to be copied. If target binding point is specified, it is assumed that a valid texture object is already bound.
  • options.sourceX (GLint, optional, default: 0) - x coordinate of the lower left corner where to start copying.
  • options.sourceY (GLint, optional, default: 0) - y coordinate of the lower left corner where to start copying.
  • options.targetX (GLint, optional) - X offset with in target texture.
  • options.targetY (GLint, optional) - Y offset with in target texture.
  • options.targetZ (GLint, optional, WebGL2) - Z offset with in target texture, when using copying into 2D Array of 3D texture.
  • options.width (GLint, optional, default: texture.width) - Width of the pixel rectangle to be copied.
  • options.height (GLint, optional, default: texture.height) - Height of the pixel rectangle to be copied.

Notes:

  • targetX, targetY, targetZ : when an offset is specified, it implies we are copying data into a sub region of the target texture and internally gl.copyTexSubImage2D or gl.copyTexSubImage3D are used based on the target, for these cases it is assumed that target texture has enough GPU memory already allocated. When none of the offsets are specified, gl.copyTexImage2D is used to copy data to entire target region and GPU memory is allocated if needed, target texture GPU memory doesn't have to be pre-allocated.

This function makes calls to the following WebGL APIs:

gl.copyTexImage2D, gl.copyTexSubImage2D and gl,copyTexSubImage3D

Blit Functions

blit(options: Object) : (WebGL2)

Copies a rectangle of pixels from a Texture or Framebuffer object into a Texture or Framebuffer object.

  • source (Texture or Framebuffer) - This object will be bound and data copied from it.
  • options.target (Texture or Framebuffer) - This object will be bound and data is copied into it.
  • options.sourceAttachment (GLenum, default: COLOR_ATTACHMENT0) - Attachment index from which data to be copied from.
  • options.sourceX0 (GLint, default: 0) - Lower X bound of copy rectangle in source.
  • options.sourceY0 (GLint, default: 0) - Lower Y bound of copy rectangle in source.
  • options.sourceX1 (GLint) - Higher X bound of copy rectangle in source.
  • options.sourceY1 (GLint) - Higher Y bound of copy rectangle in source.
  • options.targetX0 (GLint, default: 0) - Lower X bound of copy rectangle in destination.
  • options.targetY0 (GLint, default: 0) - Lower Y bound of copy rectangle in destination.
  • options.targetX1 (GLint) - Higher X bound of copy rectangle in destination.
  • options.targetY1 (GLint) - Higher Y bound of copy rectangle in destination.
  • options.mask (GLbitfild, default: 0) - A GLbitfield specifying a bitwise OR mask indicating which buffers are to be copied, possible buffers masks are GL.COLOR_BUFFER_BIT, GL.DEPTH_BUFFER_BIT and GL.STENCIL_BUFFER_BIT
  • options.color (Boolean, default: true) - When true GL.COLOR_BUFFER_BIT is added to the mask.
  • options.depth (Boolean, default: false) - When true GL.DEPTH_BUFFER_BIT is added to the mask.
  • options.stencil (Boolean, default: false) - When true GL.STENCIL_BUFFER_BIT is added to the mask.
  • options.filter=GL.NEAREST - specifies interpolation mode if stretching is needed. GL.LINEAR can be used exclusively for color buffers.

Notes:

  • There are a number of restrictions when blitting between integer and floating point formats.

This function makes calls to the following WebGL APIs:

gl.blitFramebuffer, gl.readBuffer, gl.bindFramebuffer