Advanced VIO (AVIO) functions are used to display characters. These functions must be supported for Display DCs. Hardcopy drivers do not support AVIO functions. When writing to an AVIO presentation space, an application must ensure that windows containing alphanumeric data are device-cell-aligned, where appropriate. The presentation driver can determine whether any characters that are not cell-aligned are visible. Most column, row, length, width, and height values correspond to cells within the presentation space Logical Video Buffer (LVB), whose origin is assumed to be at the bottom-left corner of the buffer (0,0).

The presentation driver is expected to clip alphanumeric data to the DC region. This is performed in the same way as it is for normal graphics, by enumerating the rectangles using GreGetClipRects and clipping each line to a single rectangle. Although the presentation driver is neither expected to test for correlation hits nor to accumulate GPI_BOUNDS, it should accumulate USER_BOUNDS for AVIO functions if the COM_ALT_BOUNDS command flag is set.

The VIO presentation space is passed to the display driver as a pointer to a VioPresentationSpace structure. The display driver uses this structure to extract the current state data to allow it to update the display. The VioPresentationSpace structure is defined as:

PresentationSpaceLock

Lock (not used by the presentation driver).

Pointer to the logical video buffer (LVB). The LVB is a two-dimensional array of character cells and is assumed to begin at offset 0 within the segment. The presentation driver must not alter the contents of this field.

Not used by the presentation driver.

Not used by the presentation driver.

Size in bytes of a cell in the LVB. This value is either 2 or 4. The presentation driver must not alter the contents of this field.

Number of cell rows in the logical video buffer. The presentation driver must not alter the contents of this field.

Number of cell columns in the logical video buffer. The presentation driver must not alter the contents of this field.

Row index for the logical video buffer. This field, together with the parameter WindowOriginColumn, indicates the logical video buffer cell that is drawn in the bottom left of the window's client area. The presentation driver must not alter the contents of this field.

Column index for logical video buffer (see WindowOriginRow). The presentation driver must not alter the contents of this field.

Row coordinate of flashing text cursor relative to the logical video buffer. The presentation driver must not alter the contents of this field.

Column coordinate of flashing text cursor relative to the logical video buffer. The presentation driver must not alter the contents of this field.

First scan line of a character-cell image overlaid by the text cursor. Lines in the cell image are numbered from top to bottom. The first line is 0. The presentation driver must not alter the contents of this field.

Last scan line of a character-cell image, overlaid by the text cursor. The presentation driver must not alter the contents of this field.

Width of text cursor in pels. The presentation driver must not alter the contents of this field.

Indicates whether the cursor is visible (nonzero) or invisible (zero). The presentation driver must not alter the contents of this field.

Height of character cell in pels. When the value passed is 0 or invalid, the presentation driver should reset it to the device default value.

Width of character cell in pels. When the value passed is 0 or invalid, the presentation driver should reset it to the device default value.

ID of current code page for this presentation space. When the value passed is 0 or invalid, the presentation driver should reset it to the device default value.

Not used by the presentation driver.

Not used by the presentation driver.

Device context handle associated with the presentation space. The presentation driver must not alter the contents of this field.

Not used by the display driver.

See "ColOrgLatch".

Window-origin coordinates (WindowOriginRow and WindowOriginColumn) saved on completion of the last call to GreUpdateCursor. RowOrgLatch and ColOrgLatch are used by the display driver to record the state of the currently displayed cursor. They are interrogated by GreUpdateCursor to determine whether the cursor has moved.

See " CursorCol".

Cursor coordinates (TextCursorRow and TextCursorColumn) saved on completion of the last call to GreUpdateCursor. These fields are used by the display driver to record the state of the currently displayed cursor so that it can be successfully erased.

See "CursorEndLine".

Cursor start and end lines (TextCursorStartLine and TextCursorEndLine) saved on completion of the last call to GreUpdateCursor. These fields are used by the display driver to record the state of the currently displayed cursor so that it can be successfully erased.

Cursor width (TextCursorWidth) saved on completion of the last call to GreUpdateCursor. This field is used by the display driver to record the state of the currently displayed cursor so that it can be successfully erased.

This is a negative value reflecting the partial cell height that must be below the bottom of the window to ensure that a complete cell is positioned at the top of the window (actual window height = WindowHeight rounded up to next complete character cell - PartialCellAdjust). The presentation driver must not alter the contents of this field.

See "YLatch".

Pel coordinates of the bottom-left corner of the cursor rectangle relative to the bottom-left corner of the window.

See "HeightLatch".

The height and width in pels of the cursor saved on completion of the last call to GreUpdateCursor. These are taken to be CellImageHeight and the difference between TextCursorStartLine and TextCursorEndLine, taking account of any wrapping. The width and height latches are used by GreUpdateCursor to record the screen region corresponding to an exclusive-OR cursor.

The height in pels of the character cell for which the cursor was last drawn. This parameter is used to detect cell height changes. These values were saved on completion of the last call to GreUpdateCursor.

Flags:

CursorShowing (0x0001)

Cursor is visible on the screen. This flag is maintained by the display driver.
fHasTheFocus (0x0002)
This window has the input focus. This flag is not modified by the display driver.
fCursorIsOn (0x0004)
Set to indicate that this is the ON phase of the blink cycle. The cursor should be invisible during the OFF phase of the blink cycle. This flag is not modified by the display driver.
pFontsLoaded[3]
Array of pointers for AVIO fonts 1, 2, and 3.
pMapFontsLoaded[3]
Array of pointers to code page maps for AVIO Fonts 1, 2, and 3.
FormatID
Presentation-space format. This identifies the format of the attribute bytes in the LVB, as follows:

0H

CGA
0H
Extended
70H
World-wide format
The presentation driver must not alter the value of this field.
lpNLSExt
Pointer to a National Language Support (NLS) extension structure where Double-Byte Character Set (DBCS) environment vectors are set for AVIO Fonts 1, 2, and 3. If the display driver is required to display DBCS, it must maintain the array of DBCSEvInfox4x, instead of DBCSEvInfox0x. When the display driver provides NLS, it must set the DBCS vectors for lcid 1-3.

Each character cell is contained in a two-byte or four-byte array in the LVB. The format of the character-cell array is:

Code Point

Position of the character in the code table.
CGA Attribute Byte
Character attributes. The four low-order bits represent the foreground color and the high-order bits represent the character background color. Each 4-bit color value corresponds to an explicit 24-bit RGB value. The RGB values are defined within the graphics engine and match the colors available on a CGA device.
Extended Attribute Byte
Applies only to four-byte cells. It is defined as:

Bit 7

Underscore.
Bit 6
Reverse video.
Bit 4
Background transparency. When set, the background is transparent. When not set, the background is opaque.
Bits 1-0
Character Set 0, 1, 2, or 3.
Extended Attribute Byte
(World-wide format). Applies only to four-byte cells. It is defined as:

Bit 7

Underscore.
Bit 6
Reverse video.
Bit 4
Background transparency. When set, the background is transparent. When not set, the background is opaque.
Bit 3
Left vertical grid.
Bit 4
Top horizontal grid.
Bits 1-0
Character Set 0, 1, 2, or 3.
Spare Attribute Byte
Applies only to four-byte character cells.

It is reserved for the system.

Spare Attribute Byte
(World-wide format). Applies only to four-byte character cells.

Bit 7

DBCS trailing byte maintained by the operating system.
Bits 6-1
Reserved for the system.
Bit 0
DBCS byte maintained by the operating system.
Note that applications are not allowed to set bit 7 and bit 0.

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