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GRAPHICS.TXT
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2001-09-30
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GRAPHICS.TXT JUN-20-87
The portability of programs using graphics should be increased. To do this,
first, a set of standardized graphics capabilities must be defined. Then,
graphics handlers must be written to translate the standard into the actual
capabilities of the available hardware.
There is a tremendous variation, and non-standardization of graphics.
IBM is already out of control with more than 16 different modes.
There are graphics screens of all dimensions, aspect ratios, and mappings.
It is undesirable to scale dimensions except by powers of 2. (It causes
glitches, and multiplication and division are unacceptably slow.)
Apple Lo-res graphics is almost never used.
Stride doesn't have graphics (except limited character graphics).
Plotters don't like to plot points (the ink doesn't flow).
Common dimensions:
320x200 IBM EGA, Amiga, Atari, Apple GS
280x192 Apple
512x342 Mac
256x192 TI
Many professional displays use horizontal dimensions of 1024, 2048, etc. and
have a 3/4 aspect ratio.
Lowest common denominator: 256x192 (4/3 aspect ratio).
(320 -256) /320 = 20%
(200 -192) /200 = 4%
Oftentimes color is unimportant.
Lowest common denominator: Black and white.
Plotters don't like to do area fill (but printers do). (Get a fat pen, area fill
is necessary for PC artwork, etc.)
Line drawings are commonly used instead of area fill.
Upper-left-hand corner is usually 0,0.
Lowest common denominator: All graphics, no text mode (do text using graphics).
BASIC OPERATIONS:
SCALE(X,Y) Powers of two only
WINDOW(X,Y,X,Y) For clipping memory address (multiple images not displayed)
multiple devices
MOVE(X,Y) Two dimensional, 256x192, power of 2 scale factor for both x & y
COLOR() Attribute, pen up/down
All kinds of attributes can be applied to lines, hence it is
best to not try to standardize them. Keep them separate.
(E.g: color, dotted, XOR, erase, bit plane address)
PATTERN
COMMON EXTENSIONS (done for efficiency):
POINT(X,Y)
LINE(X,Y)
CLEAR Area fill
CURVES Circle, arc, ellipse, ellipse at any angular orientation,
arc of ellipse
AREA FILL Rectangular areas, circular areas, flood fill
TEXT
llipse, ellipse at any angular orientation,
arc of ellipse
AREA FILL Rectangular areas, circu