\Chapter{Graphic Sheets - Basic graphic operations}

This chapter describes how graphics are accessed in {\XGAP} via the lowest
library functions for graphic sheets. These functions are used in all other 
parts of {\XGAP} and you normally only need to know them if you want to
display other things than graphic posets and subgroup lattices.

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\Section{Graphic Sheet Objects}

\FileHeader[1]{sheet}

\Declaration{GraphicSheet}

Here is the documentation for the operations to control the callback 
functions:

\Declaration{InstallCallback}
\Declaration{RemoveCallback}
\Declaration{Callback}

\FileHeader[2]{sheet}

\Declaration{IsAlive}

The following operations apply to graphic sheets:

\Declaration{Close}
\Declaration{Resize}
\Declaration{WindowId}
\Declaration{SetTitle}
\Declaration{SaveAsPS}
\Declaration{FastUpdate}

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\Section{Graphic Objects in Sheets}

\FileHeader[1]{gobject}

\Declaration{IsGraphicObject}

\bigskip%

*Constructors:*

\Declaration{Box}
\Declaration{Circle}
\Declaration{Disc}
\Declaration{Diamond}
\Declaration{Rectangle}
\Declaration{Line}
\Declaration{Text}


\bigskip%

*Operations for graphic objects:*

\Declaration{Connection}
\Declaration{Disconnect}

\Declaration{Draw}
\Declaration{Delete}[gobject]
\Declaration{Destroy}
\Declaration{Revive}
\Declaration{Move}[gobject]
\Declaration{MoveDelta}
\Declaration{PSString}
\Declaration{PrintInfo}
\Declaration{Recolor}[gobject]
\Declaration{Reshape}[gobject]
\>`\\in'{in!for graphic objects}@{`in'!for graphic objects}

This infix operation needs a vector of two integers to its left and a graphic
object to its right (``vector of two integers'' means a list of two
integers e.g. `[15,9]'). It determines, if the position given by the two
integer coordinates is inside (e.g. for boxes) or on (e.g. for lines) the
graphic objects. Returns a boolean value.
\Declaration{Change}
\Declaration{Relabel}[gobject]
\Declaration{SetWidth}[gobject]
\Declaration{Highlight}[gobject]

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\Section{Colors in XGAP}

\label{Color Models}

\FileHeader[1]{color}

\Declaration{COLORS}


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\Section{Operations for Graphic Objects}

The following table gives an overview over the supported graphic objects and 
the functions which are applicable respectively:

Here are the supported graphic object types: `Box', `Circle', `Disc', 
`Diamond', `Rectangle', `Line', `Text', `Vertex'.

These functions apply to all graphic object types:
`Draw', `Delete', `Destroy', `Revive', `Move', `MoveDelta', `PSString',
`PrintInfo', `ViewObj', `Recolor', `Reshape', `\\in', `WindowId'

In addition, the operation `Relabel' applies to objects of types `Line',
`Text', and `Vertex'; the operation `SetWidth' applies to objects of types
`Diamond', `Rectangle', `Circle', and `Line'. There is also `Change' for a
`Line' and `Highlight' for a `Vertex'.


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\Section{Global Information}

There are some global data structures which can and should be consulted if 
certain information is needed. The first (about color handling) was already 
described in section "Color Models". The second is for vertices:

\>`VERTEX'{VERTEX!record}@{`VERTEX'!record} V

  This globally bound record contains the following components:

\beginitems
`circle' & integer value for the vertex type ``circle''

`diamond' & integer value for the vertex type ``diamond''

`rectangle' & integer value for the vertex type ``rectangle''

`radius' & radius in pixels of a vertex on the screen

`diameter' & diameter in pixels of a vertex on the screen
\enditems

\bigskip%

The third structure is about the available fonts. 

\>`FONTS' V

This globally bound record has the following components: `tiny', `small', 
`normal', `large', `huge' and `fonts'. The first 5 are itself records each
for one available font. They have components `name' for the name of the font
and `fontInfo', which is a list of 3 integers. The first is the maximal size
of a character above the baseline in pixels, the second is the maximal size
of a character below the baseline in pixels, and the third is the width
in pixels of *all* characters, because it is always assumed, that the
fonts are non-proportional.

\Declaration{FontInfo}

\bigskip%

There is another global structure:

\>`BUTTONS' V

This record contains the following components: `left' and `right' contain a
number for the left resp. right mouse button. `shift' and `ctrl' contain
codes for the respective keys on the keyboard.

\bigskip%

You should always use these global data instead of hardwiring any integers into
your code.