There are a number of function call interfaces within Puzzles, and
this guide will discuss each one in a chapter of its own. After
-that, (\k{writing}) discusses how to design new games, with some
+that, \k{writing} discusses how to design new games, with some
general design thoughts and tips.
\C{backend} Interface to the back end
\S{backend-interpret-move} \cw{interpret_move()}
\c char *(*interpret_move)(game_state *state, game_ui *ui,
-\c game_drawstate *ds,
+\c const game_drawstate *ds,
\c int x, int y, int button);
This function receives user input and processes it. Its input
coordinates of the mouse pointer relative to the top left of the
puzzle's drawing area.
+(The pointer to the \c{game_drawstate} is marked \c{const}, because
+\c{interpret_move} should not write to it. The normal use of that
+pointer will be to read the game's tile size parameter in order to
+divide mouse coordinates by it.)
+
\cw{interpret_move()} may return in three different ways:
\b Returning \cw{NULL} indicates that no action whatsoever occurred
to achieve this, its \cw{flash_length()} function has to store a
flag in the \c{game_ui} to indicate which flash type is required.)
+\S{backend-status} \cw{status()}
+
+\c int (*status)(game_state *state);
+
+This function returns a status value indicating whether the current
+game is still in play, or has been won, or has been conclusively lost.
+The mid-end uses this to implement \cw{midend_status()}
+(\k{midend-status}).
+
+The return value should be +1 if the game has been successfully
+solved. If the game has been lost in a situation where further play is
+unlikely, the return value should be -1. If neither is true (so play
+is still ongoing), return zero.
+
+Front ends may wish to use a non-zero status as a cue to proactively
+offer the option of starting a new game. Therefore, back ends should
+not return -1 if the game has been \e{technically} lost but undoing
+and continuing is still a realistic possibility.
+
+(For instance, games with hidden information such as Guess or Mines
+might well return a non-zero status whenever they reveal the solution,
+whether or not the player guessed it correctly, on the grounds that a
+player would be unlikely to hide the solution and continue playing
+after the answer was spoiled. On the other hand, games where you can
+merely get into a dead end such as Same Game or Inertia might choose
+to return 0 in that situation, on the grounds that the player would
+quite likely press Undo and carry on playing.)
+
\S{backend-redraw} \cw{redraw()}
\c void (*redraw)(drawing *dr, game_drawstate *ds,
\H{backend-misc} Miscellaneous
-\S{backend-can-format-as-text} \c{can_format_as_text}
+\S{backend-can-format-as-text-ever} \c{can_format_as_text_ever}
-\c int can_format_as_text;
+\c int can_format_as_text_ever;
This boolean field is \cw{TRUE} if the game supports formatting a
game state as ASCII text (typically ASCII art) for copying to the
clipboard and pasting into other applications. If it is \cw{FALSE},
front ends will not offer the \q{Copy} command at all.
-If this field is \cw{FALSE}, the function \cw{text_format()}
-(\k{backend-text-format}) is not expected to do anything at all.
+If this field is \cw{TRUE}, the game does not necessarily have to
+support text formatting for \e{all} games: e.g. a game which can be
+played on a square grid or a triangular one might only support copy
+and paste for the former, because triangular grids in ASCII art are
+just too difficult.
+
+If this field is \cw{FALSE}, the functions
+\cw{can_format_as_text_now()} (\k{backend-can-format-as-text-now})
+and \cw{text_format()} (\k{backend-text-format}) are never called.
+
+\S{backend-can-format-as-text-now} \c{can_format_as_text_now()}
+
+\c int (*can_format_as_text_now)(game_params *params);
+
+This function is passed a \c{game_params} and returns a boolean,
+which is \cw{TRUE} if the game can support ASCII text output for
+this particular game type. If it returns \cw{FALSE}, front ends will
+grey out or otherwise disable the \q{Copy} command.
+
+Games may enable and disable the copy-and-paste function for
+different game \e{parameters}, but are currently constrained to
+return the same answer from this function for all game \e{states}
+sharing the same parameters. In other words, the \q{Copy} function
+may enable or disable itself when the player changes game preset,
+but will never change during play of a single game or when another
+game of exactly the same type is generated.
+
+This function should not take into account aspects of the game
+parameters which are not encoded by \cw{encode_params()}
+(\k{backend-encode-params}) when the \c{full} parameter is set to
+\cw{FALSE}. Such parameters will not necessarily match up between a
+call to this function and a subsequent call to \cw{text_format()}
+itself. (For instance, game \e{difficulty} should not affect whether
+the game can be copied to the clipboard. Only the actual visible
+\e{shape} of the game can affect that.)
\S{backend-text-format} \cw{text_format()}
state. It is used to implement the \q{Copy} operation in many front
ends.
-This function should only be called if the back end field
-\c{can_format_as_text} (\k{backend-can-format-as-text}) is
-\cw{TRUE}.
+This function will only ever be called if the back end field
+\c{can_format_as_text_ever} (\k{backend-can-format-as-text-ever}) is
+\cw{TRUE} \e{and} the function \cw{can_format_as_text_now()}
+(\k{backend-can-format-as-text-now}) has returned \cw{TRUE} for the
+currently selected game parameters.
The returned string may contain line endings (and will probably want
to), using the normal C internal \cq{\\n} convention. For
one-line ASCII representation, so there's no precedent yet for
whether that should come with a newline or not.)
-\S{backend-wants-statusbar} \cw{wants_statusbar()}
+\S{backend-wants-statusbar} \cw{wants_statusbar}
\c int wants_statusbar;
window it has accessed, and hence which parts need repainting. This
is done by calling \cw{draw_update()} (\k{drawing-draw-update}).
+Persistence of old drawing is convenient. However, a puzzle should
+be very careful about how it updates its drawing area. The problem
+is that some front ends do anti-aliased drawing: rather than simply
+choosing between leaving each pixel untouched or painting it a
+specified colour, an antialiased drawing function will \e{blend} the
+original and new colours in pixels at a figure's boundary according
+to the proportion of the pixel occupied by the figure (probably
+modified by some heuristic fudge factors). All of this produces a
+smoother appearance for curves and diagonal lines.
+
+An unfortunate effect of drawing an anti-aliased figure repeatedly
+is that the pixels around the figure's boundary come steadily more
+saturated with \q{ink} and the boundary appears to \q{spread out}.
+Worse, redrawing a figure in a different colour won't fully paint
+over the old boundary pixels, so the end result is a rather ugly
+smudge.
+
+A good strategy to avoid unpleasant anti-aliasing artifacts is to
+identify a number of rectangular areas which need to be redrawn,
+clear them to the background colour, and then redraw their contents
+from scratch, being careful all the while not to stray beyond the
+boundaries of the original rectangles. The \cw{clip()} function
+(\k{drawing-clip}) comes in very handy here. Games based on a square
+grid can often do this fairly easily. Other games may need to be
+somewhat more careful. For example, Loopy's redraw function first
+identifies portions of the display which need to be updated. Then,
+if the changes are fairly well localised, it clears and redraws a
+rectangle containing each changed area. Otherwise, it gives up and
+redraws the entire grid from scratch.
+
+It is possible to avoid clearing to background and redrawing from
+scratch if one is very careful about which drawing functions one
+uses: if a function is documented as not anti-aliasing under some
+circumstances, you can rely on each pixel in a drawing either being
+left entirely alone or being set to the requested colour, with no
+blending being performed.
+
In the following sections I first discuss the drawing API as seen by
the back end, and then the \e{almost} identical function-pointer
form seen by the front end.
Some platforms may perform anti-aliasing on this function.
Therefore, do not assume that you can erase a line by drawing the
-same line over it in the background colour; anti-aliasing might
-lead to perceptible ghost artefacts around the vanished line.
+same line over it in the background colour; anti-aliasing might lead
+to perceptible ghost artefacts around the vanished line. Horizontal
+and vertical lines, however, are pixel-perfect and not anti-aliased.
This function may be used for both drawing and printing.
the polygon to extend a pixel beyond its obvious bounding box as a
result of this; if you really need it not to do this to avoid
interfering with other delicate graphics, you should probably use
-\cw{clip()} (\k{drawing-clip}).
+\cw{clip()} (\k{drawing-clip}). You can rely on horizontal and
+vertical lines not being anti-aliased.
This function may be used for both drawing and printing.
This function may be used for both drawing and printing.
+\S{drawing-draw-thick-line} \cw{draw_thick_line()}
+
+\c void draw_thick_line(drawing *dr, float thickness,
+\c float x1, float y1, float x2, float y2,
+\c int colour)
+
+Draws a line in the puzzle window, giving control over the line's
+thickness.
+
+\c{x1} and \c{y1} give the coordinates of one end of the line.
+\c{x2} and \c{y2} give the coordinates of the other end.
+\c{thickness} gives the thickness of the line, in pixels.
+
+Note that the coordinates and thickness are floating-point: the
+continuous coordinate system is in effect here. It's important to
+be able to address points with better-than-pixel precision in this
+case, because one can't otherwise properly express the endpoints of
+lines with both odd and even thicknesses.
+
+Some platforms may perform anti-aliasing on this function. The
+precise pixels affected by a thick-line drawing operation may vary
+between platforms, and no particular guarantees are provided.
+Indeed, even horizontal or vertical lines may be anti-aliased.
+
+This function may be used for both drawing and printing.
+
\S{drawing-draw-text} \cw{draw_text()}
\c void draw_text(drawing *dr, int x, int y, int fonttype,
This function may be used for both drawing and printing.
+The character set used to encode the text passed to this function is
+specified \e{by the drawing object}, although it must be a superset
+of ASCII. If a puzzle wants to display text that is not contained in
+ASCII, it should use the \cw{text_fallback()} function
+(\k{drawing-text-fallback}) to query the drawing object for an
+appropriate representation of the characters it wants.
+
+\S{drawing-text-fallback} \cw{text_fallback()}
+
+\c char *text_fallback(drawing *dr, const char *const *strings,
+\c int nstrings);
+
+This function is used to request a translation of UTF-8 text into
+whatever character encoding is expected by the drawing object's
+implementation of \cw{draw_text()}.
+
+The input is a list of strings encoded in UTF-8: \cw{nstrings} gives
+the number of strings in the list, and \cw{strings[0]},
+\cw{strings[1]}, ..., \cw{strings[nstrings-1]} are the strings
+themselves.
+
+The returned string (which is dynamically allocated and must be
+freed when finished with) is derived from the first string in the
+list that the drawing object expects to be able to display reliably;
+it will consist of that string translated into the character set
+expected by \cw{draw_text()}.
+
+Drawing implementations are not required to handle anything outside
+ASCII, but are permitted to assume that \e{some} string will be
+successfully translated. So every call to this function must include
+a string somewhere in the list (presumably the last element) which
+consists of nothing but ASCII, to be used by any front end which
+cannot handle anything else.
+
+For example, if a puzzle wished to display a string including a
+multiplication sign (U+00D7 in Unicode, represented by the bytes C3
+97 in UTF-8), it might do something like this:
+
+\c static const char *const times_signs[] = { "\xC3\x97", "x" };
+\c char *times_sign = text_fallback(dr, times_signs, 2);
+\c sprintf(buffer, "%d%s%d", width, times_sign, height);
+\c draw_text(dr, x, y, font, size, align, colour, buffer);
+\c sfree(buffer);
+
+which would draw a string with a times sign in the middle on
+platforms that support it, and fall back to a simple ASCII \cq{x}
+where there was no alternative.
+
\S{drawing-clip} \cw{clip()}
\c void clip(drawing *dr, int x, int y, int w, int h);
After this call, no drawing operation will affect anything outside
the specified rectangle. The effect can be reversed by calling
-\cw{unclip()} (\k{drawing-unclip}).
+\cw{unclip()} (\k{drawing-unclip}). The clipping rectangle is
+pixel-perfect: pixels within the rectangle are affected as usual by
+drawing functions; pixels outside are completely untouched.
Back ends should not assume that a clipping rectangle will be
automatically cleared up by the front end if it's left lying around;
choose to vary line thicknesses at user request or due to printer
capabilities.
+\S{print-line-dotted} \cw{print_line_dotted()}
+
+\c void print_line_dotted(drawing *dr, int dotted);
+
+This function is called to toggle the drawing of dotted lines during
+printing. It is not supported during drawing.
+
+The parameter \cq{dotted} is a boolean; \cw{TRUE} means that future
+lines drawn by \cw{draw_line()}, \cw{draw_circle} and
+\cw{draw_polygon()} will be dotted, and \cw{FALSE} means that they
+will be solid.
+
+Some front ends may impose restrictions on the width of dotted
+lines. Asking for a dotted line via this front end will override any
+line width request if the front end requires it.
+
\H{drawing-frontend} The drawing API as implemented by the front end
This section describes the drawing API in the function-pointer form
This function behaves exactly like the back end \cw{draw_circle()}
function; see \k{drawing-draw-circle}.
+\S{drawingapi-draw-thick-line} \cw{draw_thick_line()}
+
+\c void draw_thick_line(drawing *dr, float thickness,
+\c float x1, float y1, float x2, float y2,
+\c int colour)
+
+This function behaves exactly like the back end
+\cw{draw_thick_line()} function; see \k{drawing-draw-thick-line}.
+
+An implementation of this API which doesn't provide high-quality
+rendering of thick lines is permitted to define this function
+pointer to be \cw{NULL}. The middleware in \cw{drawing.c} will notice
+and provide a low-quality alternative using \cw{draw_polygon()}.
+
\S{drawingapi-draw-update} \cw{draw_update()}
\c void (*draw_update)(void *handle, int x, int y, int w, int h);
may define this function pointer to be \cw{NULL}; it will never be
called unless printing is attempted.
+\S{drawingapi-text-fallback} \cw{text_fallback()}
+
+\c char *(*text_fallback)(void *handle, const char *const *strings,
+\c int nstrings);
+
+This function behaves exactly like the back end \cw{text_fallback()}
+function; see \k{drawing-text-fallback}.
+
+Implementations of this API which do not support any characters
+outside ASCII may define this function pointer to be \cw{NULL}, in
+which case the central code in \cw{drawing.c} will provide a default
+implementation.
+
\H{drawingapi-frontend} The drawing API as called by the front end
There are a small number of functions provided in \cw{drawing.c}
Frees a mid-end structure and all its associated data.
+\H{midend-tilesize} \cw{midend_tilesize()}
+
+\c int midend_tilesize(midend *me);
+
+Returns the \cq{tilesize} parameter being used to display the
+current puzzle (\k{backend-preferred-tilesize}).
+
\H{midend-set-params} \cw{midend_set_params()}
\c void midend_set_params(midend *me, game_params *params);
\cw{INT_MAX} as input to this function. You should probably not do
that \e{and} set the \c{user_size} flag, though!
+The midend relies on the frontend calling \cw{midend_new_game()}
+(\k{midend-new-game}) before calling \cw{midend_size()}.
+
\H{midend-new-game} \cw{midend_new_game()}
\c void midend_new_game(midend *me);
This function automatically causes a redraw, i.e. the front end can
expect its drawing API to be called from \e{within} a call to this
-function.
+function. Some back ends require that \cw{midend_size()}
+(\k{midend-size}) is called before \cw{midend_restart_game()}.
\H{midend-force-redraw} \cw{midend_force_redraw()}
from scratch before calling the game's \cw{redraw()} function.
The front end can expect its drawing API to be called from within a
-call to this function.
+call to this function. Some back ends require that \cw{midend_size()}
+(\k{midend-size}) is called before \cw{midend_force_redraw()}.
\H{midend-redraw} \cw{midend_redraw()}
redrawn will be things that have changed since the last redraw.)
The front end can expect its drawing API to be called from within a
-call to this function.
+call to this function. Some back ends require that \cw{midend_size()}
+(\k{midend-size}) is called before \cw{midend_redraw()}.
\H{midend-process-key} \cw{midend_process_key()}
front end's drawing API and/or \cw{activate_timer()}
(\k{frontend-activate-timer}).
+The return value from \cw{midend_process_key()} is non-zero, unless
+the effect of the keypress was to request termination of the
+program. A front end should shut down the puzzle in response to a
+zero return.
+
\H{midend-colours} \cw{midend_colours()}
\c float *midend_colours(midend *me, int *ncolours);
free them directly, because they will be freed automatically during
\cw{midend_free()}.
+\H{midend-which-preset} \cw{midend_which_preset()}
+
+\c int midend_which_preset(midend *me);
+
+Returns the numeric index of the preset game parameter structure
+which matches the current game parameters, or a negative number if
+no preset matches. Front ends could use this to maintain a tick
+beside one of the items in the menu (or tick the \q{Custom} option
+if the return value is less than zero).
+
\H{midend-wants-statusbar} \cw{midend_wants_statusbar()}
\c int midend_wants_statusbar(midend *me);
\cq{params:description}) describing the game currently active in the
mid-end. The returned string is dynamically allocated.
+\H{midend-can-format-as-text-now} \cw{midend_can_format_as_text_now()}
+
+\c int midend_can_format_as_text_now(midend *me);
+
+Returns \cw{TRUE} if the game code is capable of formatting puzzles
+of the currently selected game type as ASCII.
+
+If this returns \cw{FALSE}, then \cw{midend_text_format()}
+(\k{midend-text-format}) will return \cw{NULL}.
+
\H{midend-text-format} \cw{midend_text_format()}
\c char *midend_text_format(midend *me);
copying to the clipboard. The returned string is dynamically
allocated.
-You should not call this function if the game's
-\c{can_format_as_text} flag is \cw{FALSE}.
+If the game's \c{can_format_as_text_ever} flag is \cw{FALSE}, or if
+its \cw{can_format_as_text_now()} function returns \cw{FALSE}, then
+this function will return \cw{NULL}.
If the returned string contains multiple lines (which is likely), it
will use the normal C line ending convention (\cw{\\n} only). On
The front end can expect its drawing API and/or
\cw{activate_timer()} to be called from within a call to this
-function.
+function. Some back ends require that \cw{midend_size()}
+(\k{midend-size}) is called before \cw{midend_solve()}.
+
+\H{midend-status} \cw{midend_status()}
+
+\c int midend_status(midend *me);
+
+This function returns +1 if the midend is currently displaying a game
+in a solved state, -1 if the game is in a permanently lost state, or 0
+otherwise. This function just calls the back end's \cw{status()}
+function. Front ends may wish to use this as a cue to proactively
+offer the option of starting a new game.
+
+(See \k{backend-status} for more detail about the back end's
+\cw{status()} function and discussion of what should count as which
+status code.)
+
+\H{midend-can-undo} \cw{midend_can_undo()}
+
+\c int midend_can_undo(midend *me);
+
+Returns \cw{TRUE} if the midend is currently in a state where the undo
+operation is meaningful (i.e. at least one position exists on the undo
+chain before the present one). Front ends may wish to use this to
+visually activate and deactivate an undo button.
+
+\H{midend-can-redo} \cw{midend_can_redo()}
+
+\c int midend_can_redo(midend *me);
+
+Returns \cw{TRUE} if the midend is currently in a state where the redo
+operation is meaningful (i.e. at least one position exists on the redo
+chain after the present one). Front ends may wish to use this to
+visually activate and deactivate a redo button.
\H{midend-serialise} \cw{midend_serialise()}
\b fetching the \c{name} field to use in window titles and similar
\b reading the \c{can_configure}, \c{can_solve} and
-\c{can_format_as_text} fields to decide whether to add those items
-to the menu bar or equivalent
+\c{can_format_as_text_ever} fields to decide whether to add those
+items to the menu bar or equivalent
\b reading the \c{winhelp_topic} field (Windows only)
~mdw / sgt / puzzles / blobdiff