The Image Engine is designed to make the distinction between three kinds of MicroUI images:

  • the images which can be used by the application without a loading step: class Image,
  • the images which requires a loading step before being usable by the application: class ResourceImage,
  • the buffered images where the application can draw into: class BufferedImage.

The first kind of image requires the Image Engine to be able to use (get, read and draw) an image referenced by its path without any loading step. The open step should be very fast: just have to find the image in the application resources list and create an Image object which targets the resource. No RAM memory to store the image pixels is required: the Image Engine directly uses the resource address (often in FLASH memory). And finally, closing step is useless because there is nothing to free (except Image object itself, via the garbage collector).

The second kind of image requires the Image Engine to be able to use (load, read and draw) an image referenced by its path with or without any loading step. When the image is understandable by the Image Engine without any loading step, the image is considered like the first kind of image (fast open step, no RAM memory, useless closing step). When a loading step is required (dynamic decoding, external resource loading, image format conversion), the open state becomes longer and a buffer in RAM is required to store the image pixels. By consequence a closing step is required to free the buffer when image becomes useless.

The third kind of image requires, by definition, a buffer to store the image data. Image Engine must be able to use (create, read and draw) this kind of image. The open state consists in creating a buffer. By consequence a closing step is required to free the buffer when the image becomes useless. Contrary to the other kinds of images, the application will be able to draw into this image.

Functional Description

The Image Engine is composed of:

  • An “Image Generator” module, for converting images into a MicroEJ format (known by the Image Engine Renderer) or into a VEE Port binary format (cannot be used by the Image Engine Renderer), before runtime (pre-generated images).
  • The “Image Loader” module, for loading, converting and closing the images.
  • A set of “Image Decoder” modules, for converting standard image formats into a MicroEJ format (known by the Image Renderer) at runtime. Each Image Decoder is an additional module of the main module “Image Loader”.
  • The “Image Renderer” module, for reading and drawing the images in MicroEJ format.
digraph {

    graph [

    node [

    edge [

       node [color="lightblue"]
       input generator

       node [color="darkorange2"]
       loader png xxx app algo convert

       node [color="chartreuse2"]
       rom ram ext hard gpu

       node [color="gray"]

       input [label="Input Files\n(png, xxx)"]
       generator [label="Image Generator"]
       loader [label="Image Loader"]
       rom [label="Flash\n(internal ROM, NOR)"]
       ext [label="External Flash\n(SDCard etc.)"]
       ram [label="RAM"]
       app [label="Image Renderer"]
       bsp [label="BSP"]
       png [label="PNG Decoder"]
       xxx [label="XXX Decoder"]
       convert [label="MEJ Converter"]
       gpu [label="GPU"]
       algo [label="Software\nAlgorithms"]
       hard  [label="Memory Buffer"]

    input -> {rom ext generator} [ label = "png | xxx"]

    generator ->  {rom ext} [label = "png | xxx | mej | bin"]

    loader ->  png [label = "png"]
    loader ->  xxx [label = "xxx"]
    loader ->  convert [label = "mej"]
    {png xxx convert} ->  ram [label = "mej"]

    app -> bsp  [label = "mej"]

    rom ->  bsp [label = "bin"]
    rom ->  loader [label = "png | xxx | mej (to convert)"]
    rom -> app [label = "mej"]
    ram -> app [label = "mej"]

    bsp -> gpu  [label = "mej | bin"]
    bsp -> algo  [label = "mej"]

    ext ->  loader [label = "png | xxx | mej"]
    ext ->  bsp [label = "bin"]
    ext ->  app [label = "mej (byte @)"]

    {algo gpu} -> hard  [label = ""]

  • Colors:
    • blue: off-board elements (tools, files).
    • green: hardware elements (memory, processor).
    • orange: on-board Graphics Engine elements.
    • gray: BSP.
  • Line labels:
    • png: symbolizes all standard image input formats (PNG, JPG, etc.).
    • xxx: symbolizes a non-standard input format.
    • mej: symbolizes the MicroEJ output format (MicroEJ Format: Standard).
    • bin: symbolizes a VEE Port binary format (Binary Format).

Process overview:

  1. The user specifies the pre-generated images to embed (see Image Generator) and / or the images to embed as regular resources (see Encoded Image).
  2. The files are embedded as resources with the application. The files’ data are linked into the FLASH memory.
  3. When the application creates a MicroUI Image object, the Image Loader loads the image, calling the right sub Image Engine module (see Image Generator and Encoded Image) to decode the specified image.
  4. When the application draws this MicroUI Image on the display (or on buffered image), the decoded image data is used, and no more decoding is required, so the decoding is done only once.
  5. When the MicroUI Image is no longer needed, it must be closed explicitly by the application. The Image Engine Core asks the right sub Image Engine module (see Image Generator and Encoded Image) to free the image working area.


  • MicroUI module (see MicroUI),
  • Display module (see Display): the characteristics of the target display are used to configure the Image Generator.