@thi.ng/porter-duff

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About
- References
Status
Related packages
Installation
Dependencies
Usage examples
API
Authors
License

About

Porter-Duff operators for packed ints & float-array alpha compositing.

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

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

@thi.ng/pixel - Typedarray integer & float pixel buffers w/ customizable formats, blitting, drawing, convolution
@thi.ng/shader-ast-stdlib - Function collection for modular GPGPU / shader programming with @thi.ng/shader-ast

Installation

yarn add @thi.ng/porter-duff

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/porter-duff"></script>

Skypack documentation

For Node.js REPL:

const porterDuff = await import("@thi.ng/porter-duff");

Package sizes (brotli'd, pre-treeshake): ESM: 1.04 KB

Dependencies

Usage examples

Several projects in this repo's /examples directory are using this package:

Screenshot	Description	Live demo	Source
	Pixel buffer manipulations	Demo	Source
	Port-Duff image compositing / alpha blending	Demo	Source

API

Generated API docs

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.

Authors

Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-porter-duff,
  title = "@thi.ng/porter-duff",
  author = "Karsten Schmidt",
  note = "https://thi.ng/porter-duff",
  year = 2018
}