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GSX-86: Graphics for the APe
The GDOS contains the basic host-independent and device-independent graphics
functions that can be called by an application program. GDOS provides a standard
interface to graphics that is constant regardless of specific devices or host hardware,
just as the BDOS standardizes disk interfaces. Application programs access the
GDOS in much the same way that they access the BDOS.
The GDOS performs coordinate scaling so that a program can specify points in a
normalized coordinate space. It uses device-specific information to translate the
normalized coordinates into the corresponding values for each graphics device.
Multiple graphics devices can be supported under GSX-86 within a single applica-
tion. By referring to devices with a workstation identification number, an application
program can send graphics information to anyone of several devices.
The Graphics Input/Output System (GIOS) is similar to the BIOS. It contains the
device-specific code required to interface specific graphics devices to the GDOS.
The GIOS consists of a set of device drivers that communicate directly with the
graphics devices. GSX-86 requires a unique device driver for each different graphics
device on a system. The term GIOS refers to the functional layer in GSX-86 that
holds the collection of available device drivers. The particular driver that is loaded
into memory when required by an application is called a GIOS file. Although a
single program can use several graphics devices, GDOS loads only one GIOS file at
a time.
The GIOS performs the graphics primitives of GSX-86, consistent with the inherent
capabilities of a graphics device. In some cases, a device driver emulates standard
GDOS capabilities which are not provided by the graphics device hardware. For
example, some devices require that dashed lines be simulated by a series of short
vectors generated in the device driver.
Memory Management
The default device driver and GDOS are loaded directly above CPM-86 after the
GRAPHICS command has been executed. The application program is loaded in the
normal manner, starting at the top of the user area.
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