This directory contains the general device drivers ------------------------------------------------------------------------- @(#)The Structure of a Device Driver. Vogle device entries are structured as follows: three character pointers giving: the name of the device, the name for the small hardware font, and the name for the large hardware font. seventeen function pointers giving the functionality of the device. If a device is not capable of some things (eg. colour changing) a no-op function should be provided which has a return value of -1. A function must also be specified in the device driver which copies the device entry into the global device entry vdevice.dev. This function call should be included conditionally in the file drivers.c, as should the device name in the code printing the list of available devices - also found in drivers.c. The twelve functions required for a complete device driver are: DEV_char a routine which prints a character of hardware text. This routine must do any necessary moving to make sure the current drawing position on the device is correct, and it must leave the device in graphics mode. DEV_clear a routine which clears the "screen" to the current background colour. DEV_color a routine to change the current color on the device. The default colors are in the man page in the docs directory. DEV_draw a routine which draws from the current device position to a point (x, y) in vogle device coords - note these assume that (0, 0) is the bottom left hand corner. This routine must doing any necessary moving to make sure the current drawing position on the device is correct. DEV_exit a routine which does the necessary cleaning up to allow vogle to exit leaving the device in a usable form. DEV_fill a routine for doing filled polygons, devices which do not support this should just do an outline. DEV_font a routine which sets up a hardware font. This should also set vdevice.hwidth and vdevice.hheight, which are the width and height of the current hardware font in pixels. VOGLE assumes that hardware text is of a fixed width. DEV_getkey a routine which gets a single character of input from a device capable of providing it. DEV_init a routine which enables graphics on the device, sets the default colour map, and sets vdevice.maxS{x,y} and vdevice.minS{x,y} to the window size in pixels. DEV_locator a routine finds the mouse position for the device in vogle device coordinates (returned in the arguments) and returns a bit pattern giving which buttons were down at the time of the call. DEV_mapcolor a routine for changing a colormap index to a given rgb value. DEV_string a routine for printing a string of hardware text. This routine must do any necessary moving to make sure the current drawing position on the device is correct, and it must leave the device in graphics mode. DEV_backbuf a routine to initialise double buffering by selecting the back drawing buffer and performing any other initialisations. If there are any hassles with all this then it should return -1. Lot's of this double buffering isn't really double buffering at all. It's kind of a pseudo double buffering in that drawing is done off screen and copied to the screen when needed. DEV_frontbuf a routine to switch drawing into the front drawing buffer DEV_swapbuf a routine to make the back buffer visible and notionally switch the roles of the front and back drawing buffers. DEV_sync a routine to syncronize the display with what we think has been output. This function can be noop. It is used with drivers such as X11 which don't necessarily display things as soon as a call has been made to a drawing routine. Because of buffering within the system, a considerable speed up may be obtained by only syncing the display when necessary. Cases in point are: When drawing objects When drawing arcs When drawing Splines and patches where the whole lot can be "sent down the line" with a single "sync" at the end.
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