LineDisplay Capabilities

Article
10/07/2010

2/27/2008

A LineDisplay Service Object supports, at a minimum, the ability to display characters on the output device. In addition, the device may also support additional features, which the Service Object exposes to the application by setting capability properties and implementing their corresponding methods and properties.

For each additional feature, there is a capability property defined in the LineDisplayBase class. The capability properties may not be queried until the application has called Open on the Service Object. Thereafter, the capability properties will indicate which properties and methods may be set and called on the Service Object.

This section lists the features that a LineDisplay Service Object may support. For each feature, there is a capability attribute that must be set by the Service Object as well a set of properties or methods which will be used by the application to access these features. In some cases, the feature is fully supported in LineDisplayBase and requires no additional code in the Service Object class.

The capability properties are implemented as read-only in order to prevent the application from changing their values. This means, too, that they cannot be set directly by the Service Object. Instead, LineDisplayBase has a protected property, Properties, which returns a LineDisplayProperties object. This class provides public equivalents for all capability properties. For example, in order to advertise that it supports blinking, a Service Object would write:

Properties.CapBlink = true;

And not:

CapBlink = true;

Marquee-like Scrolling of the Window

The Service Object may support either horizontal or vertical marquees. If horizontal scrolling is supported, the Service Object sets Properties.CapHMarquee to true. Likewise, if vertical scrolling is supported, Properties.CapVMarquee is set to true.

Thereafter, applications and Service Objects may use the following to set or get the marquee type:

DisplayMarqueeType MaqueeType {get, set; }

Inter-Character Wait

A line display device may have the ability to wait for a specified period of time before displaying each character to create a teletype effect. If this feature is supported, the Properties.CapICharWait property is set to true.

Thereafter, applications and Service Objects may use the following to set or get the inter-character wait time:

int InterCharacterWait { get; set; }

Blinking Text

A line display device may support character-level or device-level blinking at adjustable blink rates. If this feature is supported, the Service Object should set the Properties.CapBlink property to one of the following Properties.DisplayBlink enumeration values.

DisplayBlink Value	Corresponding UPOS Value	Description
None	DISP_CR_NOBLINK	The device does not support blinking.
All	DISP_CR_BLINKALL	The device supports blinking for the entire display.
Each	DISP_CR_BLINKEACH	The device supports blinking for each individual character.

Thereafter, applications and Service Objects may use the following to set or get the blink rate:

int BlinkRate {get; set; }

Reverse Video

A line display may support character-level or device-level reverse video. If this feature is supported, the Service Object should set the Properties.CapReverse to a value in the DisplayReverse enumeration.

DisplayReverse Value	Corresponding UPOS Value	Description
None	DISP-CR_NONE	Reverse video is not supported.
All	DISP_CR_REVERSEALL	The entire contents of the display are either displayed in reserve video or displayed normally.
Each	DIS_CR_REVERSEEACH	Each character may be individually set to reverse video or normal.

The CapReverse property is used by the DisplayText method.

Device Descriptors

Descriptors are small indicators with a fixed label, and are typically used to indicate transaction states such as item, total, and change. The Service Object should set Properties.CapDescriptors to true if descriptors are supported.

Thereafter, applications and Service Objects may use the following to set, get, or clear the Descriptors:

int DeviceDescriptors {get; set; }
void ClearDescriptors();
void SetDescriptor(int descriptor, DisplaySetDescriptor attribute);

Brightness Control

All LineDisplay Service Objects support two brightness levels, normal and blank, even if not supported by the physical device. If the device supports additional brightness levels, then Properties.CapBrightness should be set to true.

Thereafter, applications and Service Objects may use the following to set or get the device brightness:

int DeviceBrightness {get; set; }

Cursor Attributes

A line display device may support a variety of different cursor types. The Properties.CapCursorType property defines which of these types are supported. The CapCursorType property is set using the DisplayCursors enumeration and holds a bitwise indication of the supported cursor types, which can be any of the following types shown in the table.

CapCursorType enum	UPOS Value	Description
Blink	DISP_CCT_BLINK	A blinking cursor is supported.
Block	DISP_CCT_BLOCK	Cursor is displayable as a block.
Fixed	DISP_CCT_FIXED	Cursor is always displayed.
HalfBlock	DISP_CCT_HALFBLOCK	Cursor is displayable as a half block.
None	DISP_CCT_NONE	Cursor is not displayable.
Other	DISP_CCT_OTHER	Cursor is displayable, but the form is unknown.
Reverse	DISP_CCT_REVERSE	Cursor is displayable in reverse video.
Underline	DISP_CCT_UNDERLINE	Cursor is displayable as an underline.

Thereafter, applications and Service Objects may use the following to set or get the cursor type:

DisplayCursors CursorType { get; set; }

Glyphs

Glyphs are a pixel-level user definition of character cells. If glyphs are supported by the device, then Properties.CapCustomGlyph should be set to true.

Thereafter, applications and Service Objects may use the following to set or get the glyph list and settings:

RangeOfCharacters [] CustomGlyphList { get; set; }
int GlyphHeight { get; }
int GlyphWidth { get; }
void DefineGlyph(int glyphCode, byte[] glyph);

Screen Modes

A device may support changing the screen mode; that is, the number of rows and columns displayed. If this feature is supported by the device, the Service Object should set Properties.CapScreenMode to true.

Thereafter, the application and Service Object may use the following to set or get the screen mode:

int ScreenMode { get; set; }
DisplayScreenMode [] ScreenModeList { get; }

Bitmaps

The Service Object should set the Properties.CapBitmap property to true if the device supports displaying bitmaps.

The Service Object may want to override the following methods if this capability is supported:

void DisplayBitmap(string fileName, int alignmentX, int alignmentY);
void DisplayBitmap(string fileName, int width, int alignmentX, int alignmentY);

Character Sets

A Service Object should set the Properties.CapCharacterSet property with the default character set capability of the line display device. This property can be set to a member of the CharacterSetCapability enumeration as shown in the following table.

CharacterSetCapability Value	UPOS Value	Description
Alpha	PTR_CCS_ALPHA	The default character set supports uppercase alphabetic plus numeric, space, minus, and period.
ANSI	N/A	This value is not used for LineDisplay devices.
ASCII	PTR_CCS_ASCII	The default character set supports 0x20 through 0x75.
Kana	PTR_CCS_KANA	The default character set supports partial code page 932, including ASCII characters 0x20 through 0x7F and the Japanese Kana characters 0xA1 through 0xDF, but excluding the Japanese Kanji characters.
Kanji	DISP_CCS_KANJI	The default character set supports code page 932 including the Shift-JIS Kanji characters, Levels 1 and 2.
Numeric	N/A	This value is not used for LineDisplay devices.
Unicode	DISP_CCS_UNICODE	The default character set supports UNICODE.
Windows	N/A	This value is not used for LineDisplay devices.

Thereafter, applications and Service Objects may use the following to set or get the character set:

int CharacterSet { get; set; }

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