@end enumerate
@end titlepage
-@node Top, Overview, (dir), (dir)
+@node Top, Acknowledgements, (dir), (dir)
@ifinfo
Scheme is the UnCommon Lisp. This Info file is the programmer reference
* Clipping of Graphics Output:: Clipping of Graphics Output
* Custom Graphics Operations:: Custom Graphics Operations
* X Graphics:: X Graphics
+* Pictures:: Pictures (MIT 6.001 implementation only)
* Starbase Graphics:: Starbase Graphics
@end menu
the documentation for its type.
@end deffn
-@node X Graphics, Starbase Graphics, Custom Graphics Operations, Graphics
+@node X Graphics, Pictures, Custom Graphics Operations, Graphics
@section X Graphics
@cindex X graphics
in documentation of the @code{XLoadQueryFont} Xlib call.
@end deffn
-@node Starbase Graphics, , X Graphics, Graphics
+@node Pictures, Starbase Graphics, X Graphics, Graphics
+@section Pictures (MIT 6.001 implementation only)
+
+@cindex pictures
+A `picture' data object is a two-dimensional array of floating point
+numbers that represents a grey-scale image on the screen. The grey
+level that the value of each element represents is determined relative
+to the range of values of the array.
+
+The width of a picture is the number of elements in each row and the height is
+the number of elements in each column. The elements are referenced by giving
+the horizontal component first and the vertical one second, with the origin at
+the bottom left corner of the displayed picture.
+
+Coordinates (i,j) are "valid coordinates" of picture p if and only if:
+
+ i,j are both exact integers and
+ 0 <= i < (picture-width p) and 0 <= j < (picture-height p)
+
+@subsection Construction of Pictures
+
+@findex make-picture
+@deffn {procedure+} make-picture X Y [K]
+ Returns a picture of width X and height Y. If K is specified then each
+ picture element is initialized to K, otherwise the value of each is
+ unspecified. X and Y must be exact integers and K must be real (if
+ specified).
+@end deffn
+
+@findex procedure->picture
+@deffn {procedure+} procedure->picture X Y F
+ F must be a real-valued function of two variables.
+ Returns a picture of width X and height Y, such that the value of each
+ element is the value of F at its indices, in floating point notation.
+
+@example
+@group
+(picture-ref (procedure->picture width height f) i j)
+@result {} (exact->inexact (f i j)) for all valid coordinates (i,j)
+@end group
+@end example
+@end deffn
+
+@cindex pgm-file
+@findex pgm-file->picture
+@deffn {procedure+} pgm-file->picture FILENAME
+ Converts a grey-scale image stored in pgm format into a picture whose
+ graphical representation will closely resemble that of the saved image.
+@end deffn
+
+@subsection Selecting Picture Components
+
+@findex picture?
+@deffn {procedure+} picture? OBJECT
+ Returns `#t' if OBJECT is a picture, otherwise returns `#f'. Note that
+ this means that the type-descriptor for OBJECT must be `eq?' to that of
+ the picture-type for this procedure to return `#t'.
+@end deffn
+
+@findex picture-width
+@findex picture-height
+@deffn {procedure+} picture-width PICTURE
+@deffnx {procedure+} picture-height PICTURE
+ These procedures return the width and height, respectively, of PICTURE.
+@end deffn
+
+@findex picture-min
+@findex picture-max
+@deffn {procedure+} picture-min PICTURE
+@deffnx {procedure+} picture-max PICTURE
+ These procedures return the least and the greatest values stored in
+ PICTURE.
+@end deffn
+
+@findex picture-ref
+@deffn {procedure+} picture-ref PICTURE I J
+ Returns the value of element (I,J) of PICTURE (always a floating point
+ number). I and J must both be valid coordinates of PICTURE.
+@end deffn
+
+@findex picture-set!
+@deffn {procedure+} picture-set! PICTURE I J K
+ Stores K at element (I,J) in PICTURE and returns an unspecified value.
+ K must be a real number and I and J must be valid coordinates of PICTURE.
+@end deffn
+
+@subsection Picture Operations
+
+@findex picture-map
+@deffn {procedure+} picture-map F PICTURE ...
+ F must be an n-ary function where n is the number of PICTURE arguments
+ passed to picture-map, and each PICTURE argument must have the same
+ dimensions. Returns a newly allocated picture with each element containing
+ the value of F applied to the list of corresponding elements of the
+ PICTURE arguments.
+
+ i.e. (picture-ref (picture-map f p1 p2 ... ) i j)
+ => (f (picture-ref p1 i j) (picture-ref p2 i j) ... ).
+@end deffn
+
+@subsection Displaying and Saving Pictures
+
+ To display pictures, a scheme graphics window must first be created.
+ Although, any scheme window may be used, the colormap will not be
+ guaranteed to be correct for grey-scale pictures, therefore the
+ recommended way of creating windows for displaying pictures is to use the
+ MAKE-WINDOW procedure.
+
+@findex picture-display
+@deffn {procedure+} picture-display W PICTURE [MIN [MAX]]
+ Displays, in the window W, the largest integer scaling of PICTURE that
+ can be contained in W. If MIN and MAX are specified then the grey levels
+ will be computed using these values as PICTURE's minimum and maximum
+ values, otherwise the actual least and greatest values of PICTURE will be
+ used. The value returned by this procedure is unspecified.
+@end deffn
+
+@cindex pgm-file
+@findex picture->pgm-file
+@deffn {procedure+} picture->pgm-file PICTURE FILENAME
+ Saves the contents of PICTURE in a file in the current directory with the
+ name FILENAME. The PICTURE is written in pgm format. If FILENAME
+ already exists, then it will be lost after evaluating this procedure.
+@end deffn
+
+@subsection Windows for Pictures
+
+@findex make-window
+@deffn {procedure+} make-window W H X Y
+ Returns a scheme graphics device of width W, height H and screen-position
+ X,Y (as would be given in an X geometry string) with a grey scale colormap
+ attached.
+@end deffn
+
+@node Starbase Graphics, , Pictures, Graphics
@section Starbase Graphics
@cindex starbase graphics
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