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\author{Fred King}
\title{The ``Fred'' level 1.5 graphics library}
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\section{Preamble}
This is a cryptic description of the ``Fred'' level 1.5 graphics library.

The library offers an alternative to EDWIN for fast level 1.5 graphics.
The routines may be accessed from IMP or Pascal.


\%include "level1:graphinc.imp"

or

\%include 'level1:graphinc.pas'

respectively.


The IFF library includes an emulation of most of these routines which will
write the same images to an .IFF file (though it won't cope with fonts).

\section{The routines (IMP)}
\small\tt \begin{verbatim}@16_E30000 %integer %array colour map(0:255)
@16_7F400 %short %integer mouse x
@16_7F402 %short %integer mouse y
%byte %integer %function mouse buttons

%integer %function  REL MOUSE X
%integer %function  REL MOUSE Y
Returns the relative change in the mouse position since last call.

%integer %function  MOUSE BUT

%routine            VLINE (%integer x, y0, y1)
Draws vertical line from (x, y0) to (x, y1).

%routine            HLINE (%integer x0, x1, y)
Draws horizontal line from (x0, y) to (x1, y).

%routine            OFFSET (%integer x, y)
Sets display area so that screen origin is at (x&(\15), y) within framestore.

%routine            COLOUR (%integer colour)
Sets colour for drawing to 'colour'.

%routine            ENABLE (%integer planes)
Allows writing to planes that have bits in 'planes' 1, disables other planes.

%routine            UPDATE COLOUR MAP (%half %integer %name new map)
Writes 256 new half word entries into the colour map from an address
starting with new map                                               

%routine            CLEAR
Sets whole of framestore to colour 0.                          
The currently selected colour and enabled palnes are unaltered.

%routine            HALF CLEAR (%integer h)
Clears half the frame store for fast animation                 
If h = 0 the box (0, 0), (687, 511) is cleared                 
If h = 1 the box (0, 512), (687, 1023) is cleared              
The currently selected colour and enabled planes are unaltered.

%routine            LINE (%integer x0, y0, x1, y1)
Draws arbitrary line from (x0, y0) to (x1, y1).

%routine            FILL (%integer x0, y0, x1, y1)
Draws filled orthogonal box with diagonal corners at (x0, y0, x1, y1).

%routine            COL FILL (%integer x0, y0, x1, y1, %byte %integer %name b)
Draws a filled orthogonal box with diagonal corners at (x0,y0, x1,y1) using
colour values from the area of memory starting with b.  B should in effect be
the first element of an array of width x1-x0+1 and height y1-y0+1.  The first
byte is the BOTTOM left corner of the box.      [jhb]

%routine            B W FILL (%integer x0, y0, x1, y1, %byte %integer %name b, t)

%routine            TRIANGLE (%integer x0, y0, x1, y1, x2, y2)
Draws filled triangle with vertices at (x0, y0), (x1, y1), (x2, y2).

%routine            TRAPEZE (%integer x00, x01, y0, x10, x11, y1)
Draws a filled trapezium with vertices (x00,y0), (x01,y0), (x10,y1), (x11,y1).

%routine            DISC (%integer x, y, r)
Draws a filled circle of radius r and centre (x, y).

%routine            RING (%integer x, y, r)
Draws the outline of a circle of radius r and centre (x, y).

%routine            DRAWARC (%integer x, y, r, x0, y0, x1, y1)
%routine            ENDARC (%integer x0, y0, x1, y1, r)
%routine            ANGLEARC (%integer x, y, r, %real phi0, phi1)
%routine            PLOT (%integer x, y)
Draws a single pixel at (x, y).

%routine            PAINT (%integer %name s, %integer x0, y0, x1, y1, offset, stride)

%routine            TEXTAT (%integer x,y)
Sets the position for drawing text to (x, y).

%routine            READFONT (%string(255) file, %integer %name font)
Reads pre-processed font from 'file' and returns heap address as integer in
'font'.

%routine            SHOWSYMBOL (%integer k)
Draws character 'k' in currently selected font at currently selected screen
position. As a result the text screen position is updated sothat subsequent
showsymbol and showstring calls draw beyond the character.                        

%routine            SHOWSTRING (%string(255) s)
Draws characters in 's' in currently selected font starting at currently
selected screen position. As a result the text screen position is updated so
that subsequent show symbol and showstring calls draw beyond the string.                            }

%routine            FONT (%integer f)
Selects font used by subsequent calls to showsymbol and show string.
'f' is the integer address returned by 'readfont', above.           
If 'f' is 0 the default Visual 200 font is selected.                

%integer %function  FONT HEIGHT
%integer %function  FONT DEPTH
%integer %function  MAX FONT WIDTH
%integer %function  MIN FONT WIDTH
%integer %function  STRING WIDTH (%string(255) s)

%integer %function  CHAR HEIGHT (%integer c)
%integer %function  CHAR DEPTH (%integer c)
%integer %function  CHAR WIDTH (%integer c)

%integer %function  TEXT X POS
%integer %function  TEXT Y POS

%routine            POLY (%integer x, y)
Defines a single vertex of (x, y) for subsequent call to closepoly. 

%routine            CLOSEPOLY
Draws a filled polygon with vertices defined by prior calls of poly. 
As a result all previous vertex definitions are lost and furthe calls
to poly specify vertices for the next polygon to be drawn.           

%constant %integer black=0, red=1, green=2, blue=4
%constant %integer yellow=red+green, magenta=red+blue, cyan=blue+green
%constant %integer white=red+green+blue

%constant %integer mouse left=1, mouse middle=2, mouse right=4

%routine            SHOW I (%integer n,p)
%routine            SHOW R (%real x, %integer n,m)
%routine            SHOW F (%real x, %integer n)
%routine            SHEX1 (%integer x)
%routine            SHEX2 (%integer x)
%routine            SHEX4 (%integer x)
%routine            SHEX (%integer x)
\end{verbatim}\rm  \normalsize 
\vspace{.75in} view:fredgraph printed on 24/02/89 at 16.36

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