AN1368 datasheet(24/34 Pages) MICROCHIP

24 / 34 page

AN1368

DS01368A-page 24

 2011 Microchip Technology Inc.

USER MESSAGE INTERFACE

The user message interface is a sublayer of the GOL

which is enabled if the GOL is used. This sublayer is

used to facilitate the message passing between

widgets and user input. For example, if the user

presses a button, then a message is sent to a call back

function, called GOLMsgCallback(), where the

message indicating that the button is pressed is

checked and an action is taken. This callback function

must be present in the application code if the GOL is

being used, no matter if message passing is being

used or not. If the message passing is not used, the

function body must return a ‘1’.

Similar to GOLDraw(), GOLMsg() must be called

continuously in a loop inside the application code to

facilitate message collection and passing.

The usage of GOLDraw(), GOLDrawCallback(),

GOLMsg()

and GOLMsgCallback() are explained in

Example 4, Example 5 and Example 6.

APPLICATION LAYER

In this layer, the user has full control of the application.

Initially, the user must initialize the Microchip Graphics

Library. The initialization is done by calling GOLInit() if

all the layers are being used, InitGraph() if the GOL

is not being used but the Primitive and Display Driver

layers are being used, or by calling ResetDevice() if

only the Display Driver layer is being used. After the

initialization routine, the Primitive and Driver layers’ APIs

can be called to achieve the required draw functionality.

To use GOL objects (like buttons), the widgets must be

created by calling the widget’s create function (e.g.,

BtnCreate()

), one by one, until all of the widgets are

created. This step will not display the widgets. The

created widgets are drawn on the screen when the

GOLDraw()

function is called repeatedly in a while loop.

The messages are processed by calling the GOLMsg()

inside the same loop, as shown in Example 5.

After GOLDraw() is done, messages are received

from the touch screen driver and hard buttons driver.

The obtained message is passed to GOLMsg() to

process and to output a widget-specific message. For

example, it converts a “USER TOUCHED POSITION

100, 100” message to BUTTON1_PRESSED.

Additionally, the application must possess the

GOLDrawCallback()

and

GOLMsgCallback()

functions.

If custom drawing is not done, then the draw callback is

used, as shown in Example 4.

EXAMPLE 4:

The message callback handles the processed

message sent out by the widgets, as shown in

Example 6.

If the application already uses a main loop,

GOLDraw()

and GOLMsg() can be called within the

loop (see Example 5).

Note 1:

Refer to the application note, AN1136, “How

to Use Widgets in Microchip Graphics

Library

” for creating a simple application.

Refer to the Microchip Graphics Library

Help file for the list of related application

notes.

WORD GOLDrawCallback(void)

{

return (1);

}

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