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MIT Scheme has a simple two-dimensional line-graphics interface that is suitable for many graphics applications. In particular it is often used for plotting data points from experiments. The interface is generic in that it can support different types of graphics devices in a uniform manner. At the present time only two types of graphics device are implemented.
Procedures are available for drawing points, lines, and text; defining the coordinate system; clipping graphics output; controlling some of the drawing characteristics; and controlling the output buffer (for devices that perform buffering). Additionally, devices may support custom operations, such as control of colors.
There are some constraints on the arguments to the procedures described
in this chapter. Any argument named graphics-device must be a
graphics device object that was returned from a call to
make-graphics-device. Any argument that is a coordinate must be
either an exact integer or an inexact real.
procedure+: graphics-type-available? graphics-device-type
This predicate returns #t if the graphics system named by the
symbol graphics-device-type is implemented by the Scheme system.
Otherwise it returns #f, in which case it is an error to attempt
to make a graphics device using graphics-device-type.
procedure+: enumerate-graphics-device-types
This procedure returns a list of symbols which are the names of all the
graphics device types that are supported by the Scheme system. The
result is useful in deciding what additional arguments to supply to
make-graphics-device, as each device type typically has a unique
way of specifying the initial size, shape and other attributes.
procedure+: make-graphics-device graphics-device-type object ...
This operation creates and returns a graphics device object.
Graphics-device-type is a symbol naming a graphics device type,
and both the number and the meaning of the remaining arguments is
determined by that type (see the description of each device type for
details); graphics-device-type must satisfy
graphics-type-available?. Graphics-device-type may also be
#f, in which case the graphics device type is chosen by the
system from what is available. This allows completely portable graphics
programs to be written provided no custom graphics operations are used.
When graphics-device-type is #f no further arguments may be
given; each graphics device type will use some "sensible" defaults.
If more control is required then the program should use one of the two
procedures above to dispatch on the available types.
This procedure opens and initializes the device, which remains valid
until explicitly closed by the procedure graphics-close.
Depending on the implementation of the graphics device, if this object
is reclaimed by the garbage collector, the graphics device may remain
open or it may be automatically closed. While a graphics device remains
open the resources associated with it are not released.
procedure+: graphics-close graphics-device
Closes graphics-device, releasing its resources. Subsequently it is an error to use graphics-device.
Each graphics device has two different coordinate systems associated with it: device coordinates and virtual coordinates. Device coordinates are generally defined by low-level characteristics of the device itself, and often cannot be changed. Most device coordinate systems are defined in terms of pixels, and usually the upper-left-hand corner is the origin of the coordinate system, with x coordinates increasing to the right and y coordinates increasing downwards.
In contrast, virtual coordinates are more flexible in the units employed, the position of the origin, and even the direction in which the coordinates increase. A virtual coordinate system is defined by assigning coordinates to the edges of a device. Because these edge coordinates are arbitrary real numbers, any Cartesian coordinate system can be defined.
All graphics procedures that use coordinates are defined on virtual coordinates. For example, to draw a line at a particular place on a device, the virtual coordinates for the endpoints of that line are given.
When a graphics device is initialized, its virtual coordinate system is
reset so that the left edge corresponds to an x-coordinate of -1,
the right edge to x-coordinate 1, the bottom edge to y-coordinate
-1, and the top edge to y-coordinate 1.
procedure+: graphics-device-coordinate-limits graphics-device
Returns (as multiple values) the device coordinate limits for graphics-device. The values, which are exact non-negative integers, are: x-left, y-bottom, x-right, and y-top.
procedure+: graphics-coordinate-limits graphics-device
Returns (as multiple values) the virtual coordinate limits for graphics-device. The values, which are real numbers, are: x-left, y-bottom, x-right, and y-top.
procedure+: graphics-set-coordinate-limits graphics-device x-left y-bottom x-right y-top
Changes the virtual coordinate limits of graphics-device to the
given arguments. X-left, y-bottom, x-right, and
y-top must be real numbers. Subsequent calls to
graphics-coordinate-limits will return the new limits. This
operation has no effect on the device's displayed contents.
Note: This operation usually resets the clip rectangle, although it is not guaranteed to do so. If a clip rectangle is in effect when this procedure is called, it is necessary to redefine the clip rectangle afterwards.
The procedures in this section provide the basic drawing capabilities of Scheme's graphics system.
procedure+: graphics-clear graphics-device
Clears the display of graphics-device. Unaffected by the current drawing mode.
procedure+: graphics-draw-point graphics-device x y
Draws a single point on graphics-device at the virtual coordinates given by x and y, using the current drawing mode.
procedure+: graphics-erase-point graphics-device x y
Erases a single point on graphics-device at the virtual coordinates given by x and y. This procedure is unaffected by the current drawing mode.
This is equivalent to
(lambda (device x y)
(graphics-bind-drawing-mode device 0
(lambda ()
(graphics-draw-point device x y))))
procedure+: graphics-draw-line graphics-device x-start y-start x-end y-end
X-start, y-start, x-end, and y-end must be real numbers. Draws a line on graphics-device that connects the points (x-start, y-start) and (x-end, y-end). The line is drawn using the current drawing mode and line style.
procedure+: graphics-draw-text graphics-device x y string
Draws the characters of string at the point (x, y) on graphics-device, using the current drawing mode. The characteristics of the characters drawn are device-dependent, but all devices are initialized so that the characters are drawn upright, from left to right, with the leftmost edge of the leftmost character at x, and the baseline of the characters at y.
The following two procedures provide an alternate mechanism for drawing lines, which is more akin to using a plotter. They maintain a cursor, which can be positioned to a particular point and then dragged to another point, producing a line. Sequences of connected line segments can be drawn by dragging the cursor from point to point.
Many graphics operations have an unspecified effect on the cursor. The following exceptions are guaranteed to leave the cursor unaffected:
graphics-device-coordinate-limits graphics-coordinate-limits graphics-enable-buffering graphics-disable-buffering graphics-flush graphics-bind-drawing-mode graphics-set-drawing-mode graphics-bind-line-style graphics-set-line-style
The initial state of the cursor is unspecified.
procedure+: graphics-move-cursor graphics-device x y
Moves the cursor for graphics-device to the point (x, y). The contents of the device's display are unchanged.
procedure+: graphics-drag-cursor graphics-device x y
Draws a line from graphics-device's cursor to the point (x, y), simultaneously moving the cursor to that point. The line is drawn using the current drawing mode and line style.
Two characteristics of graphics output are so useful that they are supported uniformly by all graphics devices: drawing mode and line style. A third characteristic, color, is equally useful (if not more so), but implementation restrictions prohibit a uniform interface.
The drawing mode, an exact integer in the range 0 to
15 inclusive, determines how the figure being drawn is combined
with the background over which it is drawn to generate the final result.
Initially the drawing mode is set to "source", so that the new output
overwrites whatever appears in that place. Useful alternative drawing
modes can, for example, erase what was already there, or invert it.
Altogether 16 boolean operations are available for combining the source (what is being drawn) and the destination (what is being drawn over). The source and destination are combined by the device on a pixel-by-pixel basis as follows:
Mode Meaning ---- ------- 0 ZERO [erase; use background color] 1 source AND destination 2 source AND (NOT destination) 3 source 4 (NOT source) AND destination 5 destination 6 source XOR destination 7 source OR destination 8 NOT (source OR destination) 9 NOT (source XOR destination) 10 NOT destination 11 source OR (NOT destination) 12 NOT source 13 (NOT source) OR destination 14 (NOT source) OR (NOT destination) 15 ONE [use foreground color]
The line style, an exact integer in the range 0 to 7
inclusive, determines which parts of a line are drawn in the foreground
color, and which in the background color. The default line style,
"solid", draws the entire line in the foreground color.
Alternatively, the "dash" style alternates between foreground and
background colors to generate a dashed line. This capability is useful
for plotting several things on the same graph.
Here is a table showing the name and approximate pattern of the different styles. A `1' in the pattern represents a foreground pixel, while a `-' represents a background pixel. Note that the precise output for each style will vary from device to device. The only style that is guaranteed to be the same for every device is "solid".
Style Name Pattern ----- ------- ------- 0 solid 1111111111111111 1 dash 11111111-------- 2 dot 1-1-1-1-1-1-1-1- 3 dash dot 1111111111111-1- 4 dash dot dot 11111111111-1-1- 5 long dash 11111111111----- 6 center dash 111111111111-11- 7 center dash dash 111111111-11-11-
procedure+: graphics-bind-drawing-mode graphics-device drawing-mode thunk
procedure+: graphics-bind-line-style graphics-device line-style thunk
These procedures bind the drawing mode or line style, respectively, of graphics-device, invoke the procedure thunk with no arguments, then undo the binding when thunk returns. The value of each procedure is the value returned by thunk. Graphics operations performed during thunk's dynamic extent will see the newly bound mode or style as current.
procedure+: graphics-set-drawing-mode graphics-device drawing-mode
procedure+: graphics-set-line-style graphics-device line-style
These procedures change the drawing mode or line style, respectively, of graphics-device. The mode or style will remain in effect until subsequent changes or bindings.
To improve performance of graphics output, most graphics devices provide some form of buffering. By default, Scheme's graphics procedures flush this buffer after every drawing operation. The procedures in this section allow the user to control the flushing of the output buffer.
procedure+: graphics-enable-buffering graphics-device
Enables buffering for graphics-device. In other words, after this procedure is called, graphics operations are permitted to buffer their drawing requests. This usually means that the drawing is delayed until the buffer is flushed explicitly by the user, or until it fills up and is flushed by the system.
procedure+: graphics-disable-buffering graphics-device
Disables buffering for graphics-device. By default, all graphics devices are initialized with buffering disabled. After this procedure is called, all drawing operations perform their output immediately, before returning.
Note: graphics-disable-buffering flushes the output buffer if
necessary.
procedure+: graphics-flush graphics-device
Flushes the graphics output buffer for graphics-device. This operation has no effect for devices that do not support buffering, or if buffering is disabled for the device.
Scheme provides a rudimentary mechanism for restricting graphics output to a given rectangular subsection of a graphics device. By default, graphics output that is drawn anywhere within the device's virtual coordinate limits will appear on the device. When a clip rectangle is specified, however, output that would have appeared outside the clip rectangle is not drawn.
Note that changing the virtual coordinate limits for a device will usually reset the clip rectangle for that device, as will any operation that affects the size of the device (such as a window resizing operation). However, programs should not depend on this.
procedure+: graphics-set-clip-rectangle graphics-device x-left y-bottom x-right y-top
Specifies the clip rectangle for graphics-device in virtual coordinates. X-left, y-bottom, x-right, and y-top must be real numbers. Subsequent graphics output is clipped to the intersection of this rectangle and the device's virtual coordinate limits.
procedure+: graphics-reset-clip-rectangle graphics-device
Eliminates the clip rectangle for graphics-device. Subsequent graphics output is clipped to the virtual coordinate limits of the device.
In addition to the standard operations, a graphics device may support
custom operations. For example, most devices have custom
operations to control color. graphics-operation is used to
invoke custom operations.
procedure+: graphics-operation graphics-device name object ...
Invokes the graphics operation on graphics-device whose name is
the symbol name, passing it the remaining arguments. This
procedure can be used to invoke the standard operations, as well as
custom operations that are specific to a particular graphics device
type. The names of the standard graphics operations are formed by
removing the graphics- prefix from the corresponding procedure.
For example, the following are equivalent:
(graphics-draw-point device x y) (graphics-operation device 'draw-point x y)
For information on the custom operations for a particular device, see the documentation for its type.
Some graphics device types support images, which are rectangular pieces of picture that may be drawn into a graphics device. Images are often called something else in the host graphics system, such as bitmaps or pixmaps. The operations supported vary between devices, so look under the different device types to see what operations are available. All devices that support images support the following operations.
operation+: graphics-device create-image width height
Images are created using the create-image graphics operation,
specifying the width and height of the image in device
coordinates (pixels).
(graphics-operation device 'create-image 200 100)
The initial contents of an image are unspecified.
create-image is a graphics operation rather than a procedure
because the kind of image returned depends on the kind of graphics
device used and the options specified in its creation. The image may be
used freely with other graphics devices created with the same
attributes, but the effects of using an image with a graphics device
with different attributes (for example, different colors) is undefined.
Under X, the image is display dependent.
operation+: graphics-device draw-image x y image
The image is copied into the graphics device at the specified position.
operation+: graphics-device draw-subimage x y image im-x im-y w h
Part of the image is copied into the graphics device at the specified (x, y) position. The part of the image that is copied is the rectangular region at im-x and im-y and of width w and height h. These four numbers are given in device coordinates (pixels).
Returns #t if object is an image, otherwise returns
#f.
procedure+: image/destroy image
This procedure destroys image, returning storage to the system.
Programs should destroy images after they have been used because even
modest images may use large amounts of memory. Images are reclaimed by
the garbage collector, but they may be implemented using memory outside
of Scheme's heap. If an image is reclaimed before being destroyed, the
implementation might not deallocate that non-heap memory, which can
cause a subsequent call to create-image to fail because it is
unable to allocate enough memory.
procedure+: image/height image
Returns the height of the image in device coordinates.
Returns the width of the image in device coordinates.
procedure+: image/fill-from-byte-vector image bytes
The contents of image are set in a device-dependent way, using one
byte per pixel from bytes (a string). Pixels are filled row by
row from the top of the image to the bottom, with each row being filled
from left to right. There must be at least (* (image/height
image) (image/width image)) bytes in bytes.
MIT Scheme supports graphics on Microsoft Windows 3.1 and Microsoft Windows NT 3.1. In addition to the usual operations, there are operations to control the size, position and colors of a graphics window. Win32 devices support images, which are implemented as device independent bitmaps (DIBs).
The Win32 graphics device type is implemented as a top level window.
graphics-enable-buffering is implemented and gives a 2x to 4x
speedup on many graphics operations. As a convenience, when buffering
is enabled clicking on the graphics window's title bar effects a
graphics-flush operation. The user has the benefit of the
increased performance and the ability to view the progress in drawing at
the click of a mouse button.
Win32 graphics devices are created by specifying the symbol win32
as the graphics-device-type argument to
make-graphics-device. The Win32 graphics device type is
implemented as a top-level window and supports color drawing in addition
to the standard Scheme graphics operations.
Graphics devices are opened as follows:
(make-graphics-device 'win32 #!optional width height palette)
where width and height specify the size, in pixels, of the drawing area in the graphics window (i.e. excluding the frame). Palette determines the colors available for drawing in the window.
When a color is specified for drawing, the nearest color available in the palette is used. Permitted values for palette are
'grayscale
'grayscale-128
'standard
#f or 'system
standard palette is
used.
Custom operations are invoked using the procedure
graphics-operation. For example,
(graphics-operation device 'set-foreground-color "blue")
operation+: win32-graphics-device set-background-color color-name
operation+: win32-graphics-device set-foreground-color color-name
These operations change the colors associated with a window.
Color-name must be of one of the valid color specification forms
listed below. set-background-color and
set-foreground-color change the colors to be used when drawing,
but have no effect on anything drawn prior to their invocation. Because
changing the background color affects the entire window, we recommend
calling graphics-clear on the window's device afterwards.
The foreground color affects the drawing of text, points, lines, ellipses and filled polygons.
Colors are specified in one of three ways:
"red", "blue", "black".
More names can be registered with the define-color operation.
#(0 0 0) is black, (0 0
128) is dark blue and #(255 255 255) is white.
If the color is not available in the graphics device then the nearest available color is used instead.
operation+: win32-graphics-device define-color name spec
Define the string name to be the color specified by spec. Spec may be any acceptable color specification. Note that the color names defined this way are available to any Win32 graphics device, and the names do not have to be defined for each device.
operation+: win32-graphics-device find-color name
Looks up a color previously defined by define-color. This returns
the color in its most efficient form for operations
set-foreground-color or set-background-color.
operation+: win32-graphics-device draw-ellipse left top right bottom
Draw an ellipse. Left, top, right and bottom indicate the coordinates of the bounding rectangle of the ellipse. Circles are merely ellipses with equal width and height. Note that the bounding rectangle has horizontal and vertical sides. Ellipses with rotated axes cannot be drawn. The rectangle applies to the center of the line used to draw the ellipse; if the line width has been set to greater than 1 then the ellipse will spill outside the bounding rectange by half of the line width.
operation+: win32-graphics-device fill-polygon points
Draws a filled polygon using the current foreground color. Points is a vector of real numbers. The numbers are in the order x1 y1 x2 y2 ... xn yn. For example,
(graphics-operation device 'fill-polygon #(0 0 0 1 1 0))draws a solid triangular region between the points (0, 0), (0, 1) and (1, 0).
operation+: win32-graphics-device load-bitmap pathname
The graphics device contents and size are initialized from the windows
bitmap file specified by pathname. If no file type is supplied
then a ".BMP" extension is added. If a clip rectangle is in
effect when this procedure is called, it is necessary to redefine the
clip rectangle afterwards.
operation+: win32-graphics-device save-bitmap pathname
The graphics device contents are saved as a bitmap to the file specified
by pathname. If no file type is supplied then a ".BMP"
extension is added. The saved bitmap may be incorporated into documents
or printed.
operation+: win32-graphics-device move-window x y
The graphics device window is moved to the screen position specified by x and y.
operation+: win32-graphics-device resize-window width height
The graphics device window is resized to the specified width and height in device coordinates (pixels). If a clip rectangle is in effect when this procedure is called, it is necessary to redefine the clip rectangle afterwards.
operation+: win32-graphics-device set-line-width width
This operation sets the line width for future drawing of lines, points and ellipses. It does not affect existing lines and has no effect on filled polygons. The line width is specified in device units. The default and initial value of this parameter is 1 pixel.
operation+: win32-graphics-device set-window-name name
This sets the window title to the string name. The window is
given the name "Scheme Graphics" at creation.
operation+: win32-graphics-device set-font handle
Sets the font for drawing text. Currently not well supported. If you can get a Win32 font handle it can be used here.
operation+: win32-graphics-device copy-area source-x-left source-y-top width height destination-x-left destination-y-top
This operation copies the contents of the rectangle specified by source-x-left, source-y-top, width, and height to the rectangle of the same dimensions at destination-x-left and destination-y-top.
MIT Scheme supports graphics in the X window system (version 11).
Arbitrary numbers of displays may be opened, and arbitrary numbers of
graphics windows may be created for each display. A variety of
operations is available to manipulate various aspects of the windows, to
control their size, position, colors, and mapping. The X graphics
device type supports images, which are implemented as Xlib XImage
objects. X display, window, and image objects are automatically closed
if they are reclaimed by the garbage collector.
A graphics device for X windows is created by passing the symbol
x as the graphics device type name to
make-graphics-device:
(make-graphics-device 'x #!optional display geometry suppress-map?)
where display is either a display object, #f, or a string;
geometry is either #f or a string; and suppress-map?
is a boolean or a vector (see below). A new window is created on the
appropriate display, and a graphics device representing that window is
returned.
Display specifies which X display the window is to be opened on;
if it is #f or a string, it is passed as an argument to
x-open-display, and the value returned by that procedure is used
in place of the original argument. Geometry is an X geometry
string, or #f which means to use the default geometry (which is
specified as a resource).
Suppress-map?, if given, may take two forms. First, it may be a
boolean: if #f (the default), the window is automatically mapped
after it is created; otherwise, #t means to suppress this
automatic mapping. The second form is a vector of three elements. The
first element is a boolean with the same meaning as the boolean form of
suppress-map?. The second element is a string, which specifies an
alternative resource name to be used for looking up the window's
resources. The third element is also a string, which specifies a class
name for looking up the window's resources. The default value for
suppress-map? is #f.
The default resource and class names are "schemeGraphics" and
"SchemeGraphics" respectively.
The window is initialized using the resource and class names specified by suppress-map?, and is sensitive to the following resource properties:
Property Class Default -------- ----- ------- geometry Geometry 512x384+0+0 font Font fixed borderWidth BorderWidth 2 internalBorder BorderWidth [border width] background Background white foreground Foreground black borderColor BorderColor [foreground color] cursorColor Foreground [foreground color] pointerColor Foreground [foreground color]
The window is created with a backing_store attribute of
Always. The window's name and icon name are initialized to
"scheme-graphics".
procedure+: x-open-display display-name
Opens a connection to the display whose name is display-name,
returning a display object. If unable to open a connection, #f
is returned. Display-name is normally a string, which is an X
display name in the usual form; however, #f is also allowed,
meaning to use the value of the unix environment variable
DISPLAY.
procedure+: x-close-display display
Closes display; after calling this procedure, it is an error to use display for any purpose. Any windows that were previously opened on display are destroyed and their resources returned to the operating system.
procedure+: x-close-all-displays
Closes all open connections to X displays. Equivalent to calling
x-close-display on all open displays.
procedure+: x-geometry-string x y width height
This procedure creates and returns a standard X geometry string from the
given arguments. X and y must be either exact integers or
#f, while width and height must be either exact
non-negative integers or #f. Usually either x and y
are both specified or both #f; similarly for width and
height. If only one of the elements of such a pair is specified,
it is ignored.
Examples:
(x-geometry-string #f #f 100 200) => "100x200" (x-geometry-string 2 -3 100 200) => "100x200+2-3" (x-geometry-string 2 -3 #f #f) => "+2-3"
Note that the x and y arguments cannot distinguish between
+0 and -0, even though these have different meanings in X.
If either of those arguments is 0, it means +0 in X
terminology. If you need to distinguish these two cases you must create
your own geometry string using Scheme's string and number primitives.
Custom operations are invoked using the procedure
graphics-operation. For example,
(graphics-operation device 'set-foreground-color "blue")
operation+: x-graphics-device set-background-color color-name
operation+: x-graphics-device set-foreground-color color-name
operation+: x-graphics-device set-border-color color-name
operation+: x-graphics-device set-mouse-color color-name
These operations change the colors associated with a window.
Color-name must be a string, which is the X server's name for the
desired color. set-border-color and set-mouse-color
immediately change the border and mouse-cursor colors.
set-background-color and set-foreground-color change the
colors to be used when drawing, but have no effect on anything drawn
prior to their invocation. Because changing the background color
affects the entire window, we recommend calling graphics-clear on
the window's device afterwards. Color names include both mnemonic
names, like "red", and intensity names specified in the
"#rrggbb" notation.
operation+: x-graphics-device set-border-width width
operation+: x-graphics-device set-internal-border-width width
These operations change the external and internal border widths of a
window. Width must be an exact non-negative integer, specified in
pixels. The change takes place immediately. Note that changing the
internal border width can cause displayed graphics to be garbled; we
recommend calling graphics-clear on the window's device after
doing so.
operation+: x-graphics-device set-font font-name
Changes the font used when drawing text in a window. Font-name must be a string that is a font name known to the X server. This operation does not affect text drawn prior to its invocation.
operation+: x-graphics-device set-mouse-shape shape-number
Changes the shape of the mouse cursor. Shape-number is an exact non-negative integer that is used as an index into the mouse-shape font; when multiplied by 2 this number corresponds to an index in the file `/usr/include/X11/cursorfont.h'.
operation+: x-graphics-device map-window
operation+: x-graphics-device withdraw-window
These operations control the mapping of windows. They correspond
directly to the Xlib procedures XMapWindow and
XWithdrawWindow.
operation+: x-graphics-device resize-window width height
Changes the size of a window. Width and height must be
exact non-negative integers. The operation corresponds directly to the
Xlib procedure XResizeWindow.
This operation resets the virtual coordinate system and the clip rectangle.
operation+: x-graphics-device move-window x y
Changes the position of a window on the display. X and y
must be exact integers. The operation corresponds directly to the Xlib
procedure XMoveWindow. Note that the coordinates x and
y do not take the external border into account, and therefore will
not position the window as you might like. The only reliable way to
position a window is to ask a window manager to do it for you.
operation+: x-graphics-device get-default resource property
This operation corresponds directly to the Xlib procedure
XGetDefault. Resource and property must be strings.
The operation returns the character string corresponding to the
association of resource and property; if no such association
exists, #f is returned.
operation+: x-graphics-device copy-area source-x-left source-y-top width height destination-x-left destination-y-top
This operation copies the contents of the rectangle specified by source-x-left, source-y-top, width, and height to the rectangle of the same dimensions at destination-x-left and destination-y-top.
operation+: x-graphics-device font-structure font-name
Returns a Scheme equivalent of the X font structure for the font named
font-name. If the string font-name does not name a font
known to the X server, or names a 16-bit font, #f is returned.
procedure+: x-font-structure/name font-structure
procedure+: x-font-structure/direction font-structure
procedure+: x-font-structure/all-chars-exist font-structure
procedure+: x-font-structure/default-char font-structure
procedure+: x-font-structure/min-bounds font-structure
procedure+: x-font-structure/max-bounds font-structure
procedure+: x-font-structure/start-index font-structure
procedure+: x-font-structure/character-bounds font-structure
procedure+: x-font-structure/max-ascent font-structure
procedure+: x-font-structure/max-descent font-structure
These procedures extract the components of the font description
structure returned by the X graphics operation font-structure. A
more complete description of these components appears in documentation
of the XLoadQueryFont Xlib call. start-index is the index
of the first character available in the font. The min-bounds and
max-bounds components are structures of type
x-character-bounds, and the character-bounds component is
a vector of the same type.
procedure+: x-character-bounds/lbearing character-bounds
procedure+: x-character-bounds/rbearing character-bounds
procedure+: x-character-bounds/width character-bounds
procedure+: x-character-bounds/ascent character-bounds
procedure+: x-character-bounds/descent character-bounds
These procedures extract components of objects of type
x-character-bounds. A more complete description of them appears
in documentation of the XLoadQueryFont Xlib call.
On Hewlett-Packard computers under the HP-UX operating system, Scheme supports graphics through the Starbase graphics library. Note that the default distribution of Scheme for HP computers does not include support for Starbase -- you must rebuild the microcode to get this support.
variable+: starbase-graphics-device-type
This is the device type for Starbase graphics devices. A Starbase device is opened as follows:
(make-graphics-device 'starbase device-name driver-name)
where device-name and driver-name are strings that are used
as the device and driver arguments to the Starbase gopen call.
The device is opened with kind OUTDEV and mode 0. The
device is initialized to have a mapping mode of DISTORT, and a
line color index of 1.
operation+: starbase-graphics-device write-image-file filename invert?
This operation writes an image of the Starbase device's display in the
file specified by filename. The image is formatted to print on an
HP Laserjet printer. Normally pixels with a color index of 0 are not
drawn by the printer, and all other pixels are; this results in the
background being white and the foreground being black in the printed
image. If invert? is not #f, this is reversed: the
background is printed as black and the foreground is not printed.
operation+: starbase-graphics-device color-map-size
Returns, as an exact non-negative integer, the number of entries in the color map for the device.
operation+: starbase-graphics-device define-color color-index red green blue
Defines the color associated with the color-map index color-index. Color-index must be an exact non-negative integer strictly less than the number of entries in the color map. Red, green, and blue must be real numbers in the range 0 to 1 inclusive, which define the color to be put in the map.
operation+: starbase-graphics-device set-line-color color-index
Changes the foreground color used in graphics operations for this device. Color-index must be an exact non-negative integer strictly less than the number of entries in the color map. Graphics drawn after this operation is invoked will appear in this new color.
The text drawn by a Starbase device is controlled by the following characteristics:
1.
.1.
0, 90, 180, and
270. 0 draws left-to-right with upright characters;
90 draws top-to-bottom with characters on their right side;
180 draws right-to-left with upside-down characters; 270
draws bottom-to-top with characters on their left side. The default
rotation is 0.
0.
operation+: starbase-graphics-device text-aspect
operation+: starbase-graphics-device text-height
operation+: starbase-graphics-device text-rotation
operation+: starbase-graphics-device text-slant
These operations return the current values of the text characteristics.
operation+: starbase-graphics-device set-text-aspect aspect
operation+: starbase-graphics-device set-text-height height
operation+: starbase-graphics-device set-text-rotation rotation
operation+: starbase-graphics-device set-text-slant slant
These operations alter the current values of the text characteristics. They have no effect on text drawn prior to their invocation.
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