AN3128 datasheet(21/105 Pages) STMICROELECTRONICS

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AN3128

Multi-input embedded GUI library firmware

Doc ID 16918 Rev 5

21/105

Multi-input embedded GUI library firmware

This section describes the API and HAL layer implementation. Each library firmware

function is described in detail. An example of how to use API functions is provided. No

example is provided for the HAL function, because the final application should manage the

graphic objects through the API layer functions only, without any direct access to the HAL

functions.

The functions are described in the following format:

4.1

Graphic object API functions

The application programming interface layer allows the final application to create pages of

graphic objects and easy use of the STMPE811 touchscreen controller. An OOP approach

is used, so it's possible for the application developer to create and use one or more

instances of a graphic object and work with pages of object without writing the code to

display the graphic objects every time the application changes the focus on another page.

Graphic object structures are seen by the application as objects with encapsulated

properties and methods. In the end, they are advanced structures containing:

●

Properties as data fields

●

Methods as function pointers

In this way each API function belongs to the related graphic object instance and so, many

graphic objects can be managed without any conflicts.

Every type of graphic object has a pre-event function that provides the process to change its

visualization on the screen and the internal status of the object; for example in a ComboBox,

when the user hits the “Down Arrow” the pre-event function changes the image associated

showing the one associated to Image2_PTR for a few moments, and sets the next option in

the list as active. This function is predefined for each type of object and very useful in order

to minimize the developer workload. In this way, the developer need only place graphic

objects on the screen page and write a function event that is called after the pre-event

function, when a touch/click event occurs between the object coordinates area.

Table 5.

Function description format

Name

Description

Function name

The name of the function

Function prototype

Prototype declaration of the function

Behavior description

Brief explanation of how the function is executed

Input parameter {x}

Description of the input parameters

Output parameter {x}

Description of the output parameters

Return value

Value returned by the function

Required preconditions

Requirements before calling the function

Called functions

Other library functions called

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