SRGP for ANSI-C (v1.0)
David Frederick Sklar
The Simple Raster Graphics Package is composed of a library of
functions, and a header file ("srgp.h") that defines custom data
types and constants, and which prototypes all SRGP routines.
This paper is a complete but extremely terse description of the
ANSI-C SRGP binding --- this is not a tutorial. If you are new
to SRGP, you must read Chapter 2 of Computer Graphics ---
Principles and Practice (Foley, van Dam, Feiner,
and Hughes, Addison-Wesley, 1990).
Contents
0. Contrast with Textbook Specification
1. States of the System
2. Canvases
3. Output
- color
- geometric data types
- control of the pattern and font tables
- control of attributes affecting output
- generation of primitives
- audio output
4. The copyPixel Procedure
5. Input
- properties of input devices
- input modes
- input devices
- control of attributes
- control of measures
- sample procedures
- event procedures
6. Inquiry
7. Control of Table Sizes
8. Diagnostics, Debugging, and Optimization
9. Miscellaneous (Hints and Caveats and etc.)
Chapter 3 of the textbook is an academic study of the issues involved in
implementing any raster graphics package; it is not a description of the
actual internal workings of any particular SRGP implementation. SRGP has been
implemented on several major types of hardware platforms, and in all cases,
low-level graphics utilities (QuickDraw on the Mac, X11 on workstations, and
MetaGraphics on the PC) were used. Because the authors of SRGP were not
involved in the implementation of the software actually drawing the primitives,
there is no pixel-level compatibility between SRGP applications running on
different platforms. Fortunately, the inconsistency in appearance will be
typically noticeable only for extreme values for attributes (very thick
primitives, rare combinations of write mode and pen/fill style, etc.).
The textbook spec did not discuss how SRGP would work in a windowing
environment. This document describes how the windowing environment affects
SRGP, and introduces a few new routines addressing window-specific problems.
The textbook's description of locator echo included "no echo" as an option
available to the application. However, it was determined that an invisible
cursor is frustrating to users of a multi-window system.
The "no echo" option is thus honored only by the PC version of SRGP.
The Mac version currently does NOT support:
pixmap patterns
non-continuous line styles for ellipses and arcs
refreshing of the screen-canvas window when it is uncovered
after being partly or fully hidden
Because the design of Color QuickDraw represents a sharp turn away from the
traditional "hands-on-the-hardware" approach of raster graphics, the Mac
version simply cannot support a great deal of SRGP's functionality. In
particular, the various non-trivial write modes (like XOR and OR)
are supported but do not
act precisely as documented. They will surprise with unpredictable results
anytime you use them when:
a) you've changed entries 0 and 1 of the color table from their default values
of white and black, and/or b) your foreground/background colors are not
currently 1/0.
The most popular use of XOR'ing --- providing a reversible method of
highlighting -- does work if you follow the above two rules AND you never
change the last two entries (e.g., entries 255 and 254 on an 8-bit-deep
machine) of the hardware
color table. Also, be aware that write modes other than REPLACE will not
make sense when drawing with pixmap patterns.
The textbook (page 33) claims that the colors black and white are 1 and 0,
respectively, at all times. This is true for all devices having color tables,
but it is sometimes false for monochrome systems that are designed for
white-on-black display.
The textbook did not describe methods for loading bitmap and pixmap patterns
into the respective pattern tables, for loading fonts into the font table, and
for loading entries in the color table. See sections 3.1 and 3.3 of this
document.
There are now "deluxe" versions of the measure records for each input device.
These should be used when timestamps and modifier-key chords are needed.
The textbook specifies the size of the screen canvas cannot be changed by
the application. That is no longer the case.
SRGP must be enabled before use, and disabled after use.
void SRGP_begin (char *name, int width, int height, int planes,
boolean enable_trace);
The window which will represent canvas 0 (the SRGP screen-canvas) is
created; its initial size is determined by the values of the second and third
parameters. The first parameter specifies a name for the application. The
fifth parameter specifies the initial status of the tracing feature, which is
described later in this section.
The fourth parameter is meaningful only on a display supporting color. It
specifies how many planes of the color table should be reserved for SRGP's use;
i.e., it places an upper bound on the number of colors that may be displayed
simultaneously in the SRGP window. (The upper bound is colors, where
is the number of planes.) The fourth parameter is ignored when the program is
run on a bilevel display.
If the program is being run on a color display, and you send the special value
"0" as the fourth parameter, SRGP will take over the entire color table,
giving your application color support as rich as the hardware can offer.
(After initializing SRGP, you can inquire the "canvas depth" to determine how
many planes are available.) The disadvantage: it will be impossible for the
user to simultaneously see the SRGP window's proper coloring and the other
clients' windows' proper coloring. Thus, you should request "0" planes only
when your application truly needs full control of the color table.
If you request more planes than available, all available planes are allocated,
just as if you requested "0" planes. Inquiry is thus your only way of
determining exactly how many planes are available.
void SRGP_tracing (boolean);
When tracing is enabled, a message is sent to a logging file (SRGPlogfile
in the current directory) each time the application calls an SRGP function;
the message includes echoing of key parameters.
IMPORTANT:
Calls to some of the input functions are NOT traced; see section 5
for details. See section 7 for more information on execution with tracing.
The initial status of tracing is set when the application calls
SRGPbegin, but it may be changed at any time via a call to
SRGPtracing.
void SRGP_allowResize (boolean);
By default, the screen-canvas window cannot be resized by the user. It is
advisable that applications live with this restriction. The rare application
that needs to allow resizing can use this routine. It is important to note
that various artifacts occur when the user actually does take advantage of this
freedom and perform a resize:
- The window is cleared to color 0; any information that was on the
screen just before the resize is lost.
- The clip rectangle attribute is not changed automatically;
the application must be responsible for changing it if necessary.
Obviously, an application that allows resizing must be informed whenever a
resize occurs, to cope with the aforementioned problems and other
application-specific ones. SRGP provides a callback utility, which allows an
application to provide a function to be called whenever a resize has occurred:
typedef int (*funcptr)();
void SRGP_registerResizeCallback (funcptr);
The application-provided callback function referred to by the function-pointer
parameter will be called whenever a resize has occurred. The callback function
will receive two integers: the new width and the new height.
void SRGP_changeScreenCanvasSize (int newwidth, int newheight);
This routine allows the application to modify the size of the screen canvas.
As a side-effect, the resize-callback function (if any) is called, just as if
the user had requested the resize.
void SRGP_enableSynchronous (void);
Allows you to enable X's synchronous mode, a useful mode for debugging.
The mode is discussed rigorously in section 3, and again in section 7.
void SRGP_end (void);
The screen-canvas window is deleted, the Mac's color table is restored
to normal, and the logging file is closed. Warning: ensure that
your application calls this in all of its exit paths! See section 9 for
related information on the adverse effects of failing to call this.
SRGP procedures operate on canvases, a canvas being a 2D array of pixels
(a virtual frame-buffer), whose depth is the number of planes requested by the
application (via the fourth parameter to SRGPbegin).
Each canvas has its own local coordinate system. The origin for the
local coordinate system is the lower-left corner of the canvas, with the
X-coordinate increasing to the right, and the Y-coordinate increasing towards
the top. The coordinates passed to all primitive-generation procedures are in
terms of the local coordinate system of the currently-active canvas.
At any given time, one canvas is active: it is the canvas being modified.
Associated with each canvas is a group of
attributes which affect all drawing into that canvas. Modification of
these attributes is only possible when the corresponding canvas is currently
active. When a canvas is created, its attribute group is initialized to
standard default values.
Each canvas is identified by a unique integer canvas index. When SRGP
is enabled, one canvas already exists and is active: the screen canvas,
having index 0, whose height and width are determined from the parameters to
SRGPbegin. The screen canvas is the only canvas which is ever
visible. No more than
MAXCANVASINDEX canvases (including the screen) may be extant
simultaneously.
Canvases may be manipulated by the following procedures:
typedef int canvasID;
canvasID SRGP_createCanvas (int width, int height);
An invisible canvas of the specified dimensions is created and its unique index
is returned. The new canvas' local-coordinate-system origin forms the
lower-left corner. forms
the upper-right corner. The pixels of a
canvas initially store color index 0. Once a canvas is created, it
can not be resized. (The screen canvas is an exception, but it can only be
resized by the user, not by the application.) Upon return, the new
canvas (and its corresponding attribute group) are active. If a new canvas
cannot be created, 0 is returned.
void SRGP_deleteCanvas (canvasID);
No canvas may be deleted while it is active. Moreover, the screen canvas
cannot be deleted with this routine.
void SRGP_useCanvas (canvasID);
The specified canvas becomes active. Primitives created subsequently are drawn
in this canvas, and attributes set subsequently modify this canvas' attribute
group.
SRGP maintains a lookup table (LUT) that maps color indices (which are
integers, used to index into the LUT) to actual colors. The number of entries
available in the lookup table is based on the number of planes allocated for
the application's use (via the fourth parameter to SRGPbegin). The
number of planes available can be inquired via:
int SRGP_inquireCanvasDepth (void);
The legal color indices are numbers between (inclusive) 0 and
. The use of color indices beyond that range are clamped
to . (Negative values are illegal and will cause
an error.)
All implementations support two colors that may be referenced using names
instead of numbers: SRGPWHITE and SRGPBLACK.
Macintosh users: See section 0 for a very important note on
restrictions inherent in the Color Quickdraw version of SRGP!
On color nodes, SRGPWHITE is 0 and SRGPBLACK is 1, and they
are the only initialized entries in the LUT. One should note, however, that if
the first two entries of the LUT are changed by the application, the names
(SRGPBLACK and SRGPWHITE) are no longer meaningful.
On monochrome displays, the two symbols SRGPBLACK and
SRGPWHITE are
implementation-dependent constants. Moreover, the use of a color index greater
than 1 is clamped to 1 on a monochrome display.
An application may load a contiguous portion of the LUT by creating three
arrays (one for red, one for blue, one for green) of intensity values,
each value being an unsigned 16-bit integer. Intensity value 0 represents that
primary's not contributing at all to the actual color, and (65,535)
represents that primary contributing its full glory to the actual color.
Note that this method for specifying colors is machine-independent;
workstations supporting only bits per intensity value will ignore all but
the most significant bits of each intensity value.
To load count entries of the LUT, starting with entry
start, create the three intensity value arrays and then call:
typedef unsigned short ush;
void SRGP_loadColorTable (int start, int count, ush *r, ush *g, ush *b);
An easy way to store "common" colors is provided by SRGP. Common colors are
those colors which have been given names (like "Purple",
"MediumForestGreen", and "Orange") by the X11 implementation. A
complete list of the supported colors is usually found in
/usr/lib/X11/rgb.txt.
in the SRGP resource file. A complete list of the supported colors is
provided below. SRGP supports only the setting of one
LUT entry at a time when using common colors:
void SRGP_loadCommonColor (int entry, char *colorname)
The supported colors are shown in their lower-case compressed forms
below. Be aware that you can insert spaces, and use upper-case
arbitrarily, in the string you hand to SRGPloadCommonColor.
aliceblue greenyellow navyblue
antiquewhite grey oldlace
aquamarine honeydew olivedrab
azure hotpink orange
beige indianred orangered
bisque ivory orchid
black khaki palegoldenrod
blanchedalmond lavender palegreen
blue lavenderblush paleturquoise
blueviolet lawngreen palevioletred
brown lemonchiffon papayawhip
burlywood lightblue peachpuff
cadetblue lightcoral peru
chartreuse lightcyan pink
chocolate lightgoldenrod plum
coral lightgoldenrodyellow powderblue
cornflowerblue lightgray purple
cornsilk lightgrey red
cyan lightpink rosybrown
darkgoldenrod lightsalmon royalblue
darkgreen lightseagreen saddlebrown
darkkhaki lightskyblue salmon
darkolivegreen lightslateblue sandybrown
darkorange lightslategray seagreen
darkorchid lightslategrey seashell
darksalmon lightsteelblue sienna
darkseagreen lightyellow skyblue
darkslateblue limegreen slateblue
darkslategray linen slategray
darkslategrey magenta slategrey
darkturquoise maroon snow
darkviolet mediumaquamarine springgreen
deeppink mediumblue steelblue
deepskyblue mediumorchid tan
dimgray mediumpurple thistle
dimgrey mediumseagreen tomato
dodgerblue mediumslateblue turquoise
firebrick mediumspringgreen violet
floralwhite mediumturquoise violetred
forestgreen mediumvioletred wheat
gainsboro midnightblue white
ghostwhite mintcream whitesmoke
gold mistyrose yellow
goldenrod moccasin yellowgreen
gray navajowhite
green navy
Warning: The Mac's color
table can sometimes be left in a disturbed state when an SRGP application
exits prematurely. See section 9 of this document for more information.
The following SRGP data types allow storage of geometric entities:
typedef struct {
int x, y;
} point;
typedef struct {
point bottom_left, top_right;
} rectangle;
Instances of these data types may be created using these routines:
point SRGP_defPoint (int x, int y);
rectangle SRGP_defRectangle (int left_x, int bottom_y, int right_x, int top_y);
Several of the SRGP attributes are patterns to be used for filling areas and
for drawing lines and frames. Two pattern tables are supported: one storing
bitmaps and one storing pixmaps.
The bitmap pattern table is initialized in this way: Pattern 0 is all
background, and pattern 1 is all foreground. Patterns 1 through 38 are the
standard Macintosh patterns shown in Volume 1 of Chernicoff's Macintosh
Revealed, and page I-474 of Inside Macintosh.
Patterns 40 through 104 are greyscale patterns increasing gradually
in intensity from all background (40) to all foreground (104).
All other entries in the bitmap pattern table are undefined; use of an
undefined pattern is a fatal error.
All other entries in the bitmap pattern table have random patterns
initially. To see an array of tiles showing the default bitmap pattern table,
run the example program
showpatterns.
Only entry 0 in the pixmap pattern table is defined, and it is simply an
all-color-0 pattern.
SRGP provides two methods for changing entries in the pattern table:
You can have SRGP load one or more patterns from a file which stores
ASCII-text pattern specifications you can create using a text editor or
convenient bitmap-editor programs (if available).
You can give SRGP a pattern specification in the form of an array of
numbers.
To load a bitmap pattern from a file, open the file and pass the stream to the function:
int SRGP_loadBitmapPatternsFromFile (FILE *stream);
The input may be composed of one or more pattern specifications ("specs").
Each spec must occupy exactly two lines and must match this format:
static char bitpat_Xy[] = {
0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??};
where X is a non-negative integer specifying the index of the entry to
be set, y is any arbitrary garbage between the integer and the left
square-brace, and 0x?? is any arbitrary byte value represented in
hexadecimal. This specification format is created
automatically by X's bitmap editor bitmap.
As a convenience, any lines beginning with are ignored, but these
comment lines must not interrupt a single two-line spec sequence. Blank unused
lines are not allowed anywhere in the file.
The closing of the input stream must be performed by the caller.
This function returns 1 if any problems at all occurred; since its parser makes
no attempt at error recovery, it is wise to check the return value.
To load a pixmap pattern from a file, use this routine whose functionality
is similar to that of the one for bitmap patterns:
int SRGP_loadPixmapPatternsFromFile (FILE *stream);
Warning: the current Macintosh version does not support this.
The input may be composed of one or more pattern specifications, each matching
this format:
static int pixpat_Xy[] = {
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?};
In this specification, each ? represents a decimal integer color index.
Applications generating the patterns at runtime can use these routines to set
one entry at a time:
void SRGP_loadBitmapPattern (int pattern_id, char *data);
void SRGP_loadPixmapPattern (int pattern_id, int *data);
The former routine expects an array of 8 characters; the latter an array of 64
integers. Warning: the current Macintosh version does not
support the loading of pixmap patterns.
Another attribute is the font to be used for text. SRGP provides a table of
fonts that may be used and modified by the application. Each entry is
identified by a unique font index (ranging from 0 to
MAXFONTINDEX).
Initially, only entry 0 of the font table is defined.
The application can modify the table via:
void SRGP_loadFont (int fontindex, char *name);
This function allows the application to load a font
into a given entry of the table.
The name of the font is simply the name of a file containing the font's
description. The filename must be absolute (begin with a slash) unless the
font lies in the default directory that is used by X in font searches.
The name of the font must comply with
the format font.size.style
where font is the name of a Macintosh font family (e.g., "Chicago"),
size is any positive number representing points, and style is a
collection of single-letter style codes:
- b for bold,
- i for italic,
- u for underline,
- o for outline,
- s for shadow,
- c for condense, or
- e for extend.
If plain text is desired, you may use the format
font.size with or without a terminating period.
These procedures allow control of the value of each attribute
associated with the currently-active canvas.
typedef enum {WRITE_REPLACE, WRITE_XOR, WRITE_OR, WRITE_AND} writeModeType;
void SRGP_setWriteMode (writeModeType);
The write mode affects the writing of a pixel, the generation of a
primitive, and the copying of a rectangular portion of a canvas. The
default is WRITEREPLACE. Please see the important note
on Mac's limited support of write modes, in section 0 of this manual.
void SRGP_setClipRectangle (rectangle);
All subsequently-created primitives and subsequent pixel-copyings are clipped
to the specified rectangle. The default clipping rectangle is exactly the size
of the associated canvas. It is illegal to set the clipping rectangle to a
rectangle which does not lie completely within the boundaries of its associated
canvas.
void SRGP_setFont (int font_index);
The application chooses from a font by giving the index (ranging from 0 to
MAXFONTINDEX) into the font table. The default is 0, the only entry
in the font table which is initialized when SRGP is launched.
void SRGP_setMarkerSize (int width_in_pixels);
This describes the dimensions of the imaginary square that circumscribes a
marker's image.
typedef enum {MARKER_CIRCLE, MARKER_SQUARE, MARKER_X} markerStyleType;
void SRGP_setMarkerStyle (markerStyleType);
SRGP supports three different marker shapes, circle being the default.
typedef enum {CONTINUOUS, DASHED, DOTTED, DOT_DASHED} lineStyleType;
void SRGP_setLineStyle (lineStyleType);
void SRGP_setLineWidth (int width_in_pixels);
The default line style is continuous, default line width is 1.
On the Macintosh, the true width of a line may be greater
than the width you specify, depending upon the line's slope.
The true width will match
the specified width only for horizontal and vertical lines.
Warning: in the Macintosh version, ellipses and arcs are always
drawn using the "continuous" line style.
void SRGP_setColor (int color_index);
This sets the foreground (drawing) color to the color that is stored at the
given entry in the LUT; the default is 1.
void SRGP_setBackgroundColor (int color_index);
Default is 0. The background color is used to color the pixels denoted by 0
values in opaque bitmap pattern fills.
void SRGP_setPlaneMask (int bitmask);
The default plane mask is all 1's.
The lowest bits of the integer bitmask
are used, where is the number of planes allocated for the application.
typedef enum {SOLID, BITMAP_PATTERN_OPAQUE, BITMAP_PATTERN_TRANSPARENT,
PIXMAP_PATTERN} drawStyle;
void SRGP_setFillStyle (drawStyle);
void SRGP_setPenStyle (drawStyle);
Fill style affects filled primitives; pen style affects outlined (framed)
primitives or lines. Text is not affected by either of these attributes.
Default is SOLID.
Pixmap patterns are currently not implemented in Mac version.
void SRGP_setFillBitmapPattern (int pattern_index);
void SRGP_setFillPixmapPattern (int pattern_index);
void SRGP_setPenBitmapPattern (int pattern_index);
void SRGP_setPenPixmapPattern (int pattern_index);
Denotes the entry in the appropriate pattern table which is to be used when the
fill or pen style is not SOLID. Pixmap patterns are
currently not implemented on the Mac.
The entire set of attributes may be set to a previously-stored group of values
using the function described next. Later in this reference is described the
function (SRGPinquireAttributes) that allows inquiry of the current
attribute group.
typedef struct ... attribute_group; /* see srgppublic.h for details */
void SRGP_setAttributes (attribute_group*);
The parameter's value should have been obtained from a
previous call to SRGPinquireAttributes.
The functions described in this section perform drawing in the currently active
canvas. For each primitive generator described, the list of attributes
affecting its operation is presented.
An ellipse is specified in terms of the rectangle within which it is inscribed.
Polygons, rectangles, and ellipses may be generated as framed or
filled. A filled primitive is all-interior --- the frame is not
displayed.
WARNING: because SRGP by default
uses X's asynchronous mode, a call to an output primitive routine may not
produce an image for an arbitrary length of time, or may not produce an image
at all! This is because in asynchronous mode, X commands are buffered, being
actually sent only when/if the buffer gets full or when/if your program
attempts to perform any kind of graphical input. If your program often uses
SRGP input devices, this should not be a problem; but, if your application is
output-only or has sleeps or long pauses not related to waiting for input, you
must explicitly flush the X buffer at appropriate times, using this function:
void SRGP_refresh (void);
Alternatively,
you can place X in synchronous mode using the routine described
in section 1. This guarantees a buffer flush after each application-level call
to SRGP output routines, but at great performance cost.
void SRGP_point (point);
void SRGP_pointCoord (int x, int y);
Current write mode, foreground color, and plane mask apply.
void SRGP_marker (point)
void SRGP_markerCoord (int x, int y)
Current marker style, marker size, write mode,
foreground color, and plane mask apply.
void SRGP_line (point pt1, point pt2);
void SRGP_lineCoord (int x1, int y1, int x2, int y2);
void SRGP_rectangle (rectangle);
void SRGP_rectanglePt (point lower_left, point upper_right);
void SRGP_rectangleCoord (int left_x, int lower_y, int right_x, int upper_y);
Current write mode, plane mask, colors, line width, line style, and pen style
apply.
void SRGP_polyPoint (int vert_count, point *vertices);
void SRGP_polyMarker (int vert_count, point *vertices);
void SRGP_polyLine (int vert_count, point *vertices);
void SRGP_polygon (int vert_count, point *vertices);
void SRGP_polyPointCoord (int vert_count, int *x_coords, int *y_coords);
void SRGP_polyMarkerCoord (int vert_count, int *x_coords, int *y_coords);
void SRGP_polyLineCoord (int vert_count, int *x_coords, int *y_coords);
void SRGP_polygonCoord (int vert_count, int *x_coords, int *y_coords);
Current write mode, plane mask, colors, line width, line style, and pen style
apply.
SRGPpolygon(Coord)
automatically connects the first and last vertices
to form a closed polygon. Lists of vertices and coordinates are limited
in size to MAXPOINTLISTSIZE.
void SRGP_ellipse (rectangle bounds);
void SRGP_ellipseArc (rectangle bounds, double startangle, double endangle);
Current write mode, plane mask, colors, line width, line style, and pen style
apply. An arc extends counterclockwise from the start angle to the end angle.
Angles are in rectangular degrees and must lie between 0 and 360, with 0
degrees being a horizontal ray extending towards positive infinity.
void SRGP_fillPolygon (int vert_count, point *vertices);
void SRGP_fillPolygonCoord (int vert_count, int *x_coords, int *y_coords);
void SRGP_fillEllipse (rectangle);
void SRGP_fillEllipseArc (rectangle bounds, double startangle, double endangle);
void SRGP_fillRectangle (rectangle);
void SRGP_fillRectanglePt (point lower_left, point upper_right);
void SRGP_fillRectangleCoord (int left_x, int lower_y, int right_x, int upper_y);
Current write mode, plane mask, colors, and fill style apply.
void SRGP_text (point origin, char *str);
Current write mode, plane mask, foreground color, and font apply. The origin
marks the leftmost point to be affected by the text, and marks the horizontal
baseline for the text, under which only the text's characters' descenders will
appear.
void SRGP_beep (void);
This procedure allows a portion of a canvas to be copied into another
part of itself or into another canvas. See the textbook for more
information on this powerful feature.
void SRGP_copyPixel (canvasID source_canvas, rectangle source_rect,
point dest_corner);
The copying operation is composed of two parts. First, a copy of a
rectangular portion of a canvas is created. Then, the copy is placed
somewhere within the currently-active canvas. (The currently-active canvas may
or may not also be the canvas providing the source of the copy.)
destcorner describes the lower-left corner of
the destination rectangle (lying inside the currently-active canvas) having the
same size as sourcerect.
Only the rectangular portion of sourcerect which lies within the
boundaries of the source canvas is copied. The placement
operation is affected by the current clipping-rectangle and write-mode.
An application program obtains input from an operator by controlling
a set of logical input devices, each representing a unique
input technique. Each device may be placed in a number of different
input modes, each representing a unique type of interaction
with the input device.
Each input device is described in terms of these
information:
a measure, a trigger set, and a set of attributes.
The measure of an input device is the value currently associated
with the device.
The trigger of an an input device is the action which indicates
a significant moment associated with the device.
The attributes of an input device are the parameters of the
device which are under application-control, primarily the echo
characteristics.
At any given time, each device is either active or
inactive. The process of activation places a device
into an active state; the process of deactivation places it into an
inactive state. Zero or more devices may be simultaneously active.
There are three modes in which input devices operate. (Initially, each device
is inactive.) The modes' names are listed below, accompanied by a
description:
INACTIVE
When device is inactive, no events are posted concerning it,
and its measure is not available to the application.
SAMPLE
When device is in Sample mode, it is active. The application may call
SRGPsample to immediately obtain the measure of input
device . The firings of -triggers do not have any
effects.
EVENT
When device is in Event mode, it is active.
The firing of an -trigger
causes an input report (containing the measure of the device at
the time of the firing) to be appended to the input queue.
The following function allows control of the input
modes and echoing for all input devices:
typedef enum {NO_DEVICE, LOCATOR, KEYBOARD} inputDevice;
typedef enum {INACTIVE, SAMPLE, EVENT} inputMode;
void SRGP_setInputMode (inputDevice, inputMode);
The specified input device is placed in the specified mode. Whenever device
's mode is changed from Inactive to either Sample or Event, the device
is activated: its measure is initialized (to a static default initial
value, or to a value specified by the application while the device was
inactive) and echoing begins. When 's mode is set to Event, queueing
of the device's event reports is enabled as well. When 's mode is
changed from Event, all queued events for that device are discarded.
When 's mode is set to Inactive, the device is
deactivated: trigger firings from the device are ignored and
echoing is disabled.
The SRGP input devices are described in this section.
LOCATOR
The measure of the Locator device incorporates a position expressed in the
coordinate system of the screen canvas, a chord giving the status of the mouse
buttons, and the number of the button which most recently experienced a
transition. The button-chord array is indexed using three constants:
LEFT_BUTTON, MIDDLE_BUTTON, and
RIGHT_BUTTON. The Macintosh version treats the sole mouse
button as the left button, and pretends the middle and right
are always "up".
The button-mask attribute of this device determines which of the buttons
are of interest when the device is active in Event mode: only buttons specified
in this mask can trigger an event.
typedef enum {UP, DOWN} buttonStatus;
typedef struct {
point position;
buttonStatus button_chord[3];
int button_of_last_transition;
} locator_measure;
The "deluxe" version of the locator measure includes
a chord giving the status of three primary modifier keys at the time of the
last button transition, and a timestamp structure. The modifier chord array is
indexed via
SHIFT, CONTROL, and META.
(Warning:
the physical key to which the META modifier maps varies from system
to system; moreover, some window manager setups will swallow button presses
modified by these keys, and thus applications that rely on modifier keys lose
some portability.)
(The META key is labelled "option" on the Macintosh keyboards.)
The timestamp specifies the time at which the most recent
change to the measure occurred --- i.e., successive sampling of a
non-moving locator produces a "constant" timestamp.
typedef struct {
int seconds; duration since application launch
int ticks; a tick is 1/60th second
} srgp_timestamp;
typedef struct {
point position;
buttonStatus button_chord[3];
int button_of_last_transition;
buttonStatus modifier_chord[3]; status at last transition
srgp_timestamp timestamp;
} deluxe_locator_measure;
KEYBOARD
The measure of this device is a character string, storing either
a single ASCII character code or a sequence of printable characters.
The "deluxe" version of the measure includes the modifier chord, a
timestamp, and a locator position:
typedef struct {
char *buffer; ptr to space allocated by application
int buffer_length; set by application
buttonStatus modifier_chord[3];
point position;
srgp_timestamp timestamp;
} deluxe_keyboard_measure;
The processing-mode attribute of this device determines which of the two
meanings is given to the measure of the device:
RAW:
When a key is hit, the measure stores a string of length 1 whose single element
is the ASCII character code of the key hit (taking into account the status of
the shift and control modifier keys) and a trigger-firing
occurs. The modifier chord shows the status of the modifiers when the key was
hit. No echo occurs in RAW mode.
EDIT:
(the default)
When a key representing a printable character is hit and the string is
not yet full, the character is appended to the string. When the
backspace key is hit, the last character of the string is
deleted. When return is hit, an event is sent (representing the full
value of the string) and the measure is set to the null string. In EDIT mode,
the modifier chord is not maintained and should be ignored.
C programmers should take care to allocate a buffer large enough to include the
null character that terminates the string measure. For example, two bytes
are needed to store a RAW-mode measure.
The following procedures set the attributes for input devices.
Attributes may be set at any time, regardless of whether the device is
active or inactive.
void SRGP_setLocatorButtonMask (int value);
The value should be 0 or an OR combination of one or more of the following
defined constants: LEFT_BUTTON_MASK, MIDDLE_BUTTON_MASK, and
RIGHT_BUTTON_MASK.
Initially the value is LEFT_BUTTON_MASK:
meaning only the left button (which is the only button on a 1-button mouse)
generates events.
SRGP_setLocatorEchoType (int value); /* CURSOR, RUBBER_LINE, or RUBBER_RECT */
An application can choose to have just the cursor, or to also have a
rubber-primitive (anchored at a fixed point with the other end of the primitive
following the cursor's movement).
Note: the value NOECHO is also accepted,
but it is ignored on all platforms except the IBM PC.
SRGP provides a cursor table whose 0th entry is initialized to an arrow; all
other entries are unusable until loaded.
void SRGP_loadCursorTable (int cursor_index, int shape);
/* shape: any constant defined in <X11/cursorfont.h> */
Legal cursor indices are numbers between 0 and MAXCURSORINDEX,
inclusive. The shape may be any constant defined in the
"cursorfont.h" file that is provided by X11. The shape may be one of
the following: 1 for the standard Mac "I-beam" text cursor, 2 for a cross, 3
for a "plus" cursor, and 4 for a watch icon. The shape may also be the
resource ID of a customized cursor placed as a "CURS" resource in the
application's resource file.
The attributes for the locator's echo are set via:
void SRGP_setLocatorEchoCursorShape (int cursor_index);
void SRGP_setLocatorEchoRubberAnchor (point position);
The keyboard's attributes are set via:
typedef enum {EDIT, RAW} keyboardMode;
void SRGP_setKeyboardProcessingMode (keyboardMode);
void SRGP_setKeyboardEchoColor (int color_index);
void SRGP_setKeyboardEchoFont (int font_index);
void SRGP_setKeyboardEchoOrigin (point position);
Keyboard echo attributes are only meaningful when the keyboard is
active in EDIT processing mode. Setting the keyboard's processing mode
(default EDIT) clears
the keyboard's measure as a side-effect.
The measure of a device may be changed by the application at any time.
If the change is performed while the device is active, the measure
immediately changes, as does as echoing concerning the device.
If it is done while the device is inactive, the specified measure is
used to initialize the device's measure the next time it is activated.
NOTE: the button-related fields of the locator measure may not be
changed by the application.
void SRGP_setLocatorMeasure (point value);
void SRGP_setKeyboardMeasure (char *value);
The involved input device must be in SAMPLE mode. Each function places in the
provided place the current measure of the corresponding device. Calls to
these routines are NOT traced.
The SRGPsampleKeyboard function copies the keyboard measure into the
given character-array buffer of size bufferlength. If the current
keyboard measure is longer than (bufferlength1) bytes, it is
truncated. Similarly, the keyboard-measure structure sent to
SRGPsampleDeluxeKeyboard must
have pre-set values for its buffer
and bufferlength fields.
void SRGP_sampleLocator (locator_measure *measure);
void SRGP_sampleKeyboard (char *buffer, int buffer_length);
void SRGP_sampleDeluxeLocator (deluxe_locator_measure *measure);
void SRGP_sampleDeluxeKeyboard (deluxe_keyboard_measure *measure);
Calls to these functions are NOT traced.
inputDevice SRGP_waitEvent (int maximum_wait_time);
If, upon entry, the event queue is not empty, the procedure exits immediately,
identifying the event report at the head of the queue and removing the report
from the queue. Otherwise, the application enters a wait state, which is
exited upon the first occurrence of a trigger-firing from any device which is
currently in EVENT mode. The wait state never lasts for more than the number
of ticks (1/60 seconds) given in the
maximumwaittime parameter (which,
when negative, represents infinity). An application can "poll" the queue
(avoiding a wait state) by specifying "0" as the maximum wait time.
The return value identifies the device causing the event. The special value
NODEVICE
is returned when the procedure exits due to timeout.
When an application discovers that an input event (not a timeout) caused the
return of SRGPwaitEvent, it may obtain the data associated with the
involved event by using the appropriate "get" function, whose parameters and
return values mimic those of the sample functions:
void SRGP_getLocator (locator_measure *measure);
void SRGP_getKeyboard (char *measure, int buffer_length);
void SRGP_getDeluxeLocator (deluxe_locator_measure *measure);
void SRGP_getDeluxeKeyboard (deluxe_keyboard_measure *measure);
NOTE: Calls to these routines are NOT traced.
void SRGP_inquireAttributes (attribute_group *group);
The current states of all
attributes are copied into the provided group structure. For information on
the names of the fields in the structure, see srgppublic.h.
canvasID SRGP_inquireActiveCanvas (void);
This function allows inquiry of the ID of the currently-active canvas.
rectangle SRGP_inquireCanvasExtent (canvasID);
void SRGP_inquireCanvasSize (canvasID, int *width, int *height);
Two functions allowing inquiry of the size of a canvas.
int SRGP_inquireCanvasDepth (void);
Returns the number of planes available in all canvases.
void SRGP_inquireTextExtent (char *str, int *width, int *ascent, int *descent);
This procedure allows inquiry of the rectangular extent which would be covered
by the output of the given character string with the current font attribute.
The tables that store patterns, fonts, etc. have default sizes that in many
cases are acceptable. You may, however, choose to reduce the size of a table
to save memory (if you're working on a Mac Plus, for instance) or increase the
size of a table if you need more entries. You may change the size of a table
only before SRGP is initialized!
void SRGP_setMaxCanvasIndex (int i);
void SRGP_setMaxPatternIndex (int i);
void SRGP_setMaxCursorIndex (int i);
void SRGP_setMaxFontIndex (int i);
void SRGP_setMaxPointlistSize (int i);
See srgpsphigs.h for
the defaults for these sizes. NOTE: Do not reduce
the size of the pattern table!
SRGP offers two features that aid the developer in debugging an application.
Both of these features may be disabled or enabled by the programmer and even by
the user at run-time, in order to optimize the execution.
The first feature is tracing. When enabled, each call to an SRGP
routine (except a few input-related routines) produces a detailed
message in a log file. A parameter to SRGPbegin() controls the
initial state of tracing; calls to SRGPtracing can be used to control
the state during runtime. Early test runs of an application should always be
performed with tracing enabled. For more details on tracing, see Section 1.
The second feature is parameter verification. All SRGP routines perform
verification of all parameters (except those that are pointers to an
array or structure) before they commence operation. All errors are fatal and
produce a crash with a detailed error message. Only when a program is fully
debugged should optimization efforts include disabling parameter verfication!
You may permanently disable verification and tracing via:
void SRGP_disableDebugAids (void);
If your application crashes due to an X server error or in the scope of an SRGP
routine, there are two possibilities (assuming the X server is not at fault):
You passed invalid data to an SRGP routine, via a parameter that is
not subject to SRGP's verification. For example, SRGP assumes the sanity of
pointers it receives (e.g., pointer to a vertex list).
There is a bug in SRGP. To help the system administrator locate or
report the bug, edit the application to use the following sequence to
initialize, and run the program with tracing and parameter verification
enabled:
SRGP_beginWithDebug (name, w, h, p, TRUE);
SRGP_enableSynchronous();
About SRGP's diagnostics: There are two types of run-time errors. The first
type is parameter-verification errors; the verification can be turned off as
mentioned earlier. The second type occurs when a problem unrelated to bad
input occurs, like running out of memory when attempting to allocate a canvas.
All errors -- of both types -- are considered fatal by default, and cause a
crash after displaying an informative message to the user. Some programmers
might wish to make all errors be non-fatal, so program execution can continue
(with suitable recovery algorithms, of course). The following routine
can be used to choose between fatal and non-fatal error handling:
typedef enum {FATAL_ERRORS, NON_FATAL_ERRORS} errorHandlingMode;
void SRGP_setErrorHandlingMode (errorHandlingMode);
When an error is detected by SRGP while the mode is NONFATALERRORS,
no message is issued to the user; rather, a
global variable is set to a positive integer that represents the error:
#include "srgp_errtypes.h"
extern int SRGP_errorOccurred;
The header file contains symbolic constants mapping the integers to error
types. The global variable is never reset to 0 by SRGP; the application is
responsible for examining and resetting it. Obviously, non-fatal mode should
be used with great care, and only late in an application's development.
An SRGP application cannot control multiple windows: only canvas 0 is
represented by a visible window.
Keep the difference between synchronous and asynchronous modes in mind: if a
brief application produces no output, it may be because the X command buffer is
not being flushed. For more information, see section 3.4.
On color machines, if the SRGP application requests full color support (by
passing 0 as the fourth parameter to SRGPbegin), the windows of
clients other than the SRGP application will not show their "true" colors
whenever the cursor lies within the SRGP window; likewise, the SRGP window will
show false colors whenever the cursor lies outside its extent. This can be
disconcerting, and an application that does not need full use of the color
table should instead reserve a subpart of the color table by sending a positive
integer to SRGPbegin. (Note: if your application does not call
SRGPwaitEvent often enough, SRGP will not be notified of the cursor's
location, and thus it may not be able to restore true colors when the cursor
enters the SRGP window.)
Note that color indices are integers (rather than unsigned longs, as in X).
This means that in the rare event that one is using a machine with a 32-bit
deep framebuffer but with only 16-bit integers, the full set of LUT entries
will not be available.
Most machines support X's backing-store feature; on these machines, SRGP
refreshes its window whenever any part that was previously covered is
re-exposed, or whenever it is de-iconized. On other machines, the graphic
information in the window is volatile and is lost whenever it is covered or
iconized.
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