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About

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This package provides all 13 fundamental Porter-Duff compositing / blending operators, and utilities to pre/post-multiply alpha. All operators are available for packed ARGB/ABGR 32bit packed ints or RGBA float vectors.

References

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Installation

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Dependencies

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API

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Basic usage

import * as pd from "@thi.ng/porter-duff";

// packed int version (premultiplied ARGB)
pd.SRC_OVER_I(0x80800000, 0xcc0cc00)

// automatically premultiply inputs & post-multiply result
pd.porterDuffPInt(pd.SRC_OVER_I, 0x80ff0000, 0xcc00ff00);

// the above is same as:
pd.postmultiplyInt(
    pd.SRC_OVER_I(
        pd.premultiplyInt(0x80ff0000),
        pd.premultiplyInt(0xcc00ff00)
    )
)

// premultiplied float version [R,G,B,A]
pd.SRC_OVER_F([1, 0, 0, 0.5], [0, 1, 0, 0.8]);

Operators

Integer operators are suffixed with _I, float versions with _F. Consult above diagram for expected results.

  • CLEAR
  • SRC
  • DEST
  • SRC_OVER
  • DEST_OVER
  • SRC_IN
  • DEST_IN
  • SRC_OUT
  • DEST_OUT
  • SRC_ATOP
  • DEST_ATOP
  • XOR
  • PLUS

Custom operators

New operators (e.g. for blend modes) can be easily defined via porterDuff / porterDuffInt. Both functions take 2 function arguments to extract blend coefficients from the src & dest colors:

import { porterDuffInt } from "@thi.ng/porter-duff";

// coefficient functions take the normalized alpha values
// of both colors as arguments, but unused here...
const customOp = porterDuffInt(() => -0.5, () => 1);

custom operator

The following coefficient functions are included by default (and are used by all standard operators):

  • ZERO => 0
  • ONE => 1
  • A => alpha of src color
  • B => alpha of dest color
  • ONE_MINUS_A => 1 - alpha of src color
  • ONE_MINUS_B => 1 - alpha of dest color

Additional operators / modifiers

The following modifiers are also discussed in the original Porter-Duff paper (linked above).

  • darken / darkenInt
  • dissolve / dissolveInt
  • opacity / opacityInt

Pre/post-multiplied colors

All Porter-Duff operators expect colors with pre-multiplied alpha. Premultiplication is also recommended for transparent WebGL textures (especially when using mipmaps). For that purpose the following helpers might be useful:

  • premultiply / premultiplyInt
  • postmultiply / postmultiplyInt
  • isPremultiplied / isPremultipliedInt

Furthermore, existing PD operators can be wrapped with automatic pre/post-multiplies using porterDuffP / porterDuffPInt (see example above).

Note: HTML Canvas ImageData is using non-premultiplied colors.