## Graphics Adapter Device Driver Reference

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### Glossary - C

C

cached micro presentation space - A presentation space from a Presentation Manager owned store of micro presentation spaces. It can be used for drawing to a window only, and must be returned to the store when the task is complete.

CDB - Command Descriptor Block.

cell - See character cell.

character box - (1) An imaginary parallelogram on a display surface that contains all parts of one graphic character. Synonymous with bounding box. (T) (2) The maximum area in which a symbol and all associated elements, such as a cursor, an underline, or space surrounding the symbol to separate it from other symbols, can be printed or displayed. Synonymous with character cell. (3) The imaginary parallelogram whose boundaries govern the size, orientation, and spacing of individual characters to be displayed on a graphics display device.

character cell - (1) An addressable location on a display surface or printing medium. (2) The physical width and height in pels of a font. See also bounding box. (3) The imaginary box whose boundaries govern the size , orientation, and spacing of individual characters to be displayed on a workstation.

character mode - A mode that, in conjunction with the font type, determines the extent to which graphics characters are affected by the character box, shear, and angle attributes.

clipping - In computer graphics, removing those parts of display elements that lie outside of given boundary.

clip limits - The area of the paper that can be reached by a printer or plotter.

clipping path - A clipping boundary in world-coordinate space.

code page - An assignment of graphic characters and control function meanings to all code points; for example, assignment of characters and meanings to 256 code points for an 8-bit code, assignment of characters and meanings to 128 code points for a 7-bit code.

code point - A 1-byte code representing one of 256 potential characters.

code segment - An executable section of programming code within a load module.

color conversion - Changing one color format to another. Required, for example, when the source color format is different from the destination color format. When going from the monochrome color format to the color format, 1 (one) bits are converted to the image foreground color, and 0 ( zero) bits are converted to the image background color.

When going from color to monochrome, all pels that match the passed background color are converted to the image background color of the destination.

All other pels are converted to the image foreground color of the destination. The color conversion takes place prior to any mix mode.

color dithering - See dithering.

command code - In this specification, refers to a group of related commands that an adapter device driver can receive.

All command codes have a prefix of "IOCC_". For example, common I/O requests (such as Read, Write, etc.) are grouped under the command code IOCC_EXECUTE_IO.

command data block - A data structure defined by the Small Computer System Interface standard to send commands to devices that conform to SCSI standards.

command descriptor block (CDB) - The structure used to communicate commands from a source to a destination.

command modifier - In this specification, a specific operation that an adapter device driver is to perform.

All command modifiers have a prefix of "IOCM_". For example, an adapter device driver might receive an IOCC_EXECUTE_IO command with a command modifier of IOCM_READ.

compatibility kernel - The portion of the OS/2 kernel that exists to support DOS INT 20, 21, 25, 26, and 27 functions. It acts as an interface to common kernel functionality such as the file system.

CON - Character-device name reserved for the console keyboard and screen.

conditional compilation - Processing by the preprocessor of certain specified code in the file, depending on the evaluation of a specified condition.

context hook - Similar to a "force flag" in earlier versions of OS/2. These are events, signaled by a virtual device driver, that are processed at task time. Forcing an IRET, and simulating an NMI, can fall into this category.

control program - A computer program designed to schedule and to supervise the execution of programs of a computer system.

controller sector buffer - One or more buffers, managed by a hardware adapter, to improve I/O transfer rates by helping to match a device and software timing requirements.