The Font Loader is a module of the MicroUI runtime, dedicated to the internal font format, that loads font data (precomputed bitmaps of glyphs) ready to be displayed.
The font data must be stored as a resource (in EJF raw format).
Typically, these resources are generated by the Font Generator and embedded as internal resources or loaded from external memories (External Resources loader).
The Font Loader is able to load some fonts located outside the CPU addresses’ space range.
It uses the External Resource Loader.
When a font is located in such memory, the font characters are loaded one by one from the External Memory.
The Font Loader uses a RAM buffer (External Font Heap) containing only the font character currently being drawn by the application.
It is unloaded from the RAM when the Graphics Engine’s software algorithms no longer need it.
The External Font Heap is stored into a RAM section called .bss.microui.display.externalFontsHeap.
Its size is automatically calculated according to the external fonts used by the firmware.
This size can be checked when enabling the verbose mode when building the application executable:
However, it is possible to change this value by setting the application property ej.microui.memory.externalfontsheap.size.
This option is very useful when building a kernel: the kernel may anticipate the section size required by the features.
Warning
When this size is smaller than the size required by an external font, some characters may be not drawn.
Also, the Font Loader copies a very short part of the resource (the font file) in RAM (into CPU address space range): the font header.
This header remains located in RAM as long as the application is using the font.
As soon as the application uses another external font, the new font replaces the old one.
Like internal resources, the Font Generator uses a configuration file (also called the “list file”) for describing fonts that need to be processed.
The list file must be specified in the application launcher (see Standalone Application Options).
However, all the files in the application classpath with the suffix .fontsext.list are automatically parsed by the Font Generator tool.
This chapter describes the steps to setup the loading of an external resource from the application:
Add the font to the application project resources (typically in the source folder src/main/resources and in the package fonts).
Create / open the configuration file (e.g. application.fontsext.list).
Add the relative path of the font and, at least, its output format (e.g. /fonts/myFont.ejf::4, see Fonts).
Build the application: the Font Generator converts the font in RAW format in the external resources folder ([application_output_folder]/externalResources).
Deploy the external resources to the external memory (SDCard, flash, etc.) of the device.
The Simulator automatically manages the external resources like internal resources.
All fonts listed in *.fontsext.list files are copied in the external resources folder, and this folder is added to the Simulator’s classpath.
As explained here, the notion of Dynamic styles and the style UNDERLINED are not supported anymore by MicroUI 3. However, an external font may have been generated with an older version of the Font Generator; consequently, the generated file can hold the Dynamic style.
The Font Loader can load these old versions of fonts.
However, there are some runtime limitations:
The Dynamic styles are ignored.
The font is drawn without any dynamic algorithm.
The font style (the style returned by Font.isBold() and Font.isItalic()) is the Dynamic style.
For instance, when a font holds the style bold as dynamic style and the style italic as built-in style, the font is considered as bold + italic; even if the style bold is not rendered.
