Summary

Graphics Objects are predefined entities provided by the MLA which are drawn on the display under the control of an embedded application. Graphics objects make data seen by the application program visible to the user. If the system has a touch screen capability, Graphics objects can also be used to input user commands.

Although previously designed Graphics Object can be easily modified to suit the visual requirements of an application.

This section of the tutorial covers:

• Creating Graphics Objects
• Drawing Graphics Objects on the screen
• Controlling the appearance of Graphics Objects

Updating the values displayed by the Object and getting user input from the objects are covered in the next two sections of this tutorial.

Examples of Graphics Objects

The list of available graphics objects include:

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.

Object Creating Functions

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

Object	Create Function	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

Example: Creating a Screen With Two 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 slider, GFX_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:

Style Scheme

Structure of a Style Scheme

The structure GFX_GOL_OBJ_SCHEME is used to hold instances of style schemes. GFX_GOL_OBJ_SCHEME is defined in GFX_GOL_SCHEME.h.

Styles schemes contain at least 16 items. Additional items will be added if Alpha Blending defined in GFX_CONFIG.h or Gradient Color Filling defined in GFX_CONFIG.h are enabled.

When an object is displayed, elements from the style scheme are applied to object based upon the state bits of the object.

Structure Member	Function
EmbossDkColor	Dark color used for the 3-D effect of the object.
EmbossLtColor	Light color used for the 3-D effect of the object.
TextColor0	Generic text colors used by the objects. Usage may vary from one object type to another
TextColor1	Generic text colors used by the objects. Usage may vary from one object type to another
TextColorDisabled	Text color used when the object state bit is set to "disabled"
Color0	Generic color used to render objects. Usage may vary from one object type to another
Color1	Generic color used to render objects. Usage may vary from one object type to another
ColorDisabled	Color used to render objects that are disabled
pFont	Pointer to the font table used by the object
fillStyle	Determines gradient type. Only used when Color Gradients are enabled
ComonBkColor	Used to hide objects from view without deleting them.
ComonBkLeft	Horizontal starting point of the background
ComonBkTop	Vertical starting point of the background
ComonBkType	Specifies the type of background to use.
*ComonBkImage	pointer to an image used as the background image
EmbossSize	Size of the pannel for 3-D effects. Will be set to 0 if 3D is not used.
AlphaValue	Alpha value used for alpha blending, this is only available only when GFX_CONFIG_ALPHABLEND_DISABLE is not commented out in gfx_config.h
gradientStartColor	Starting color for gradient color scheme. Only exists when GFX_CONFIG_GRADIENT_DISABLE is not commented out in gfx_config.h
gradientEndColor	Ending color for gradient color scheme. Only exists when GFX_CONFIG_GRADIENT_DISABLE is not commented out in gfx_config.h

Default Style Scheme

Creating and Using Style Schemes

It is quite common for an application to use several different style schemes. To create a style scheme, several steps must be taken:

1. Create an instance of the style scheme structure and give it a name.
2. Populate the newly created structure with the desired style scheme elements.
3. Assign the new style scheme as graphic objects are created.

For instances where only a few elements of a new style scheme differ from an existing style scheme, many programmers find it more convenient to copy an existing scheme into a newly defined scheme, then edit the few different elements.

Example: Creating and Using a Custom Style Scheme

The following steps presume the gfx_gol_scheme_default file has been added to the project, resulting in the creation of a default scheme GOLSchemeDefault.

State Bits

Every graphics object has several state bits. The state bits are combined together into one word and stored in the object's data structure. State bits fall into one of two different categories:

The first category informs the drawing function, GFX_GOL_ObjectListDraw, to copy the entire object, or a portion of the object, to the frame buffer.

The second category of status bits informs GFX_GOL_ObjectListDraw how to draw the object. When an object is being copied to the frame-buffer some of the state bits inform GFX_GOL_ObjectListDraw which elements from the style scheme are to be applied to the object.

State Bits used to Draw or Re-draw an Object

GOL_OBJ_xxxx_DRAW_STATE and GOL_OBJ_xxxx_DRAW_UPDATE_STATE are the state bits used to determine if an object is to be drawn or redrawn to the frame buffer.

All objects have a DRAW state bit. When this bit is set, the entire object is written (or re-written) to the frame buffer. Typically, the user program sets the DRAW bit when a situation occurs in which the entire object needs to be redrawn.

Some objects have an UPDATE status bit in addition to the DRAW bit. When the update bit is set by the user application, only the portion of the object which contains data (such as the value on the meter object) will be re-drawn to the frame buffer. Using the UPDATE bit will help reduce the visual "jitter" that some people notice when an entire object is redrawn.

Object	DRAW State bit	UPDATE State bit
Button	GFX_GOL_BUTTON_DRAW_STATE	n/a
Meter	GFX_GOL_METER_DRAW_STATE	GFX_GOL_METER_UPDATE_DRAW
Scroll Bar	GFX_GOL_SCROLLBAR_DRAW_STATE	GFX_GOL_SCROLLBAR_THUMB_DRAW_STATE
Static Text Box	GFX_GOL_STATICTEXT_DRAW_STATE	n/a
Progress Bar	GFX_GOL_PROGRESSBAR_DRAW_STATE	GFX_GOL_PROGRESSBAR_DRAW_BAR_STATE

State Bits Used to Control an Object's Appearance

In addition to the draw and update state bits, Graphics objects each have the following bits:

• GFX_GOL_xxxx_DISABLED: Draws the object with ColorDisabled and TextColorDisabled
• GOLgfx_xxxx_HIDE: Draws the object with the CommonBkColor from the style scheme, making the object non-visible
• GFX_GOL_xxxx_FOCUS: Applies a focus element to the object

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In addition to the draw and update state bits, each object type has some states unique to that object. These unique state bits reflect conditions applicable to those objects. Comparison of the state bits for a Button object and a Scroll-bar object reveals some of the differences:

Button States	Scroll-bar States
Object Specific States in yellow:

The function and effect of setting the object-specific state bits vary from object to object. This tutorial will show you the procedures used to set and clear state bits. Refer to the help file to learn about the attributes of object-specific state bits.

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