Graphics Library
The external graphics library is a complement to the types in the standard library. It provides the ability to load and save images from a number of common file formats.
The graphics library is located in the package graphics, and entirely implemented in a single
shared library. Since this is an external library, it does not need to be distributed alongside
applications where it is not needed.
The library provides a convenient API for common operations. This API consists of the following functions:
-
graphics.Image loadImage(core.io.IStream from)Load an image from a
core.io.IStream. The function inspects the first few bytes of the image to determine its format. For this reason, the stream needs to support peeking around 10 bytes from the current location and onwards.Throws an
graphics.ImageLoadErroron failure. -
graphics.Image loadImage(core.io.Url file)Wrapper to load a file from an
Url. Equivalent to callingloadImage(file.read()), but checks that the file exists before attempting to open it in order to generate better error messages. -
void saveImage(graphics.Image image, core.io.Url file)Save an image to a file. The library uses the extension of the file name to select an appropriate decoder and save the file.
The library also provides a more advanced API for more control over the process. This API centers
around the type graphics.ImageFormat, which represents an image format. You can then
call the options member to create an graphics.FormatOptions instance that lets you
either load a file and inspect the settings used to compress the file, or to set the settings and
then save an image using those.
The library has the following functions for listing image formats:
-
core.Array<graphics.ImageFormat> supportedImageFormats()This function returns an array of all supported image formats. This makes it possible to enumerate all currently supported formats, for example to use in a file selection dialog.
-
void registerImageFormat(graphics.ImageFormat format)Allows registering custom image formats with the library so that other parts of the system may use them.
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core.Maybe<graphics.ImageFormat> findFormat(core.io.IStream from)Select a format that can decompress the image in the stream by inspecting its header. This is what
loadImagedescribed above uses to decompress images. -
core.Maybe<graphics.ImageFormat> findFormat(core.Str fileExt)Select a format that is suitable for the file extension (case insensitive) passed to the function. This is what
saveImageabove uses.
On Linux, the graphics library uses libpng for decoding PNG images, and libjpegturbo for JPEG
images. On Windows, the Windows Imaging API is used. BMP, PPM, and ICO use custom implementations that
support the most common image types. For example, this means that compressed BMP formats will not
work.
Loading Icons
At the moment, the ico file format is the only supported format that may contain more than one
image. When an ico file is loaded using loadImage, the highest resolution version is picked by
default. If you wish to access all versions of the image, use loadImageSet instead of loadImage
and loadSet instead of load.
For convenience, the graphics library also provides a
reader for ico files. As such, it is possible
to place ico files in a package, and the Graphics library will load it for you automatically. The
icon will be placed in the name tree in the form of a function that returns an
graphics.ImageSet that represents the icon. The function will create a copy of the
image, so you are free to modify it if you wish.