libpng provides Scala Native bindings for the libpng C library for reading and writing PNGs.

The goal of this project is to provide an easy-to-use Scala Native facade for the majority libpng, the official PNG reference library. Currently, many of the functions needed to read and write PNGs are covered. Also, convenience methods are provided to read into and write from an image buffer. The simplified API offered by the C library has not yet been covered, but is planned.

The more "programmer friendly" part of this library is found in the io.github.edadma.libpng package. That's the only package you need to import from, as seen in the example below. The other package in the library is io.github.edadma.libpng.extern which provides for interaction with the libpng C library using Scala Native interoperability elements from the so-call unsafe namespace. There are no public declarations in the io.github.edadma.libpng package that use unsafe types in their parameter or return types, making it a pure Scala facade. Consequently, you never have to worry about memory allocation or type conversions.

To use this library, libpng-dev needs to be installed:

sudo apt install libpng-dev

Include the following in your project/plugins.sbt:

addSbtPlugin("com.codecommit" % "sbt-github-packages" % "0.5.2")

Include the following in your build.sbt:

resolvers += Resolver.githubPackages("edadma")

libraryDependencies += "io.github.edadma" %%% "libpng" % "0.1.0"

Use the following import in your code:

import io.github.edadma.libpng._

The following example shows the use of convenience methods to read and write a PNG file to and from an image buffer. The example reads a PNG image file image.png, and modifies it, pixel by pixel, to remove all the red from it and to make the amount of green at each pixel equal to the amount of blue. The image is then written to a new PNG file new.png.

import io.github.edadma.libpng._

object Main extends App {

  val image = read("image.png")

  if (image.format != ImageFormat.RGBA)
    sys.error("can only process RGBA type files")

  for (i <- 0 until image.width; j <- 0 until image.height) {
    image.setRGBARed(i, j, 0)
    image.setRGBAGreen(i, j, image.getRGBABlue(i, j))
  }

  write("new.png", image)

}

As to performance, if you use nativeMode := "release-fast" in your build.sbt, then this example runs as fast as the corresponding C program would.

API documentation is forthcoming, however documentation for the C library is found here.

ISC