Creating Graphics Objects

Graphics Objects are created at run-time. Before a screen is initially drawn, the application calls a sequence of object-creating functions. Each of these functions creates a data structure for an instance of an object. Parameters passed to the object creating functions determine the location, size, state, and colors of the object. In addition to the commonly shared parameters just mentioned, many object functions accept parameters unique to the specific objects.

The created data structures are placed in a single linked list. The drawing function (GFX_GOL_ObjectListDraw) reads the objects state bits in the display list, then updates the frame buffer as needed.

All object creating functions return a pointer to the memory location of the data structure they create. The object structures are kept in the heap memory of the PIC® MCU's RAM.

Before Graphics Objects can be used the developer must modify the MPLAB® X IDE's project to setup the heap. The specific heap size needed by a Graphics application can be determined by clicking here.

Object Creating Functions

Below is a partial list of the functions used to create object:

Object Create
Object Unique Input Parameters
Button GFX_GOL_ButtonCreate() radius - the roundness of the buttons
Digital Meter GFX_GOL_DigitalMeterCreate() value - initial value
NoOfDigits - number of digits
DotPos - location of decimal point
Scroll Bar GFX_GOL_ScrollBarCreate() range - highest possible value
page - incremental value change
pos - initial slider position
Group Box GFX_GOL_GroupboxCreate() alignment - text alignment designation for the group box
Check Box GFX_GOL_CheckBoxCreate() n/a
To get a complete list of all Primitive Graphics functions you can open GFX_help.png help_mlagfx.jar
located in..microchip/mla/vYYYY_MM_DD/doc…

Example: Creating a screen with 2 Buttons and a Slider


When preparing to use graphic objects in a project, two steps need to be taken:

  • Ensure GFX_GOL.h and GFX_GOL.c are added to the project
  • Add the source and header file for the particular object in the file. For example: since the steps below show at least one button and one sliderGFX_GOL__Button.c / GFX_GOL_Button.h and GFX_GOL_ScrollBar.c / GFX_GOL_ScrollBar.h need to be added to the project.

When drawn to the screen the structure created by the function Create_Screen (below) will display:


In the example above, Create_Screen calls several instances of object-creating functions. When an object is created, the creating function returns a pointer to the location in memory where the object has been placed. If for some reason the object is not successfully made, then a NULL is returned. In this example, the function Create_Screen is written to return a "true" if all the objects were successfully created. If any object was not able to be created, then Create_Screen will return a 'false'.

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