GUI routines

Allegro contains an object-oriented dialog manager, which was originally based on the Atari GEM system (form_do(), objc_draw(), etc: old ST programmers will know what I'm talking about :-) You can use the GUI as-is to knock out simple interfaces for things like the test program and grabber utility, or you can use it as a basis for more complicated systems of your own. Allegro lets you define your own object types by writing new dialog procedures, so you can take complete control over the visual aspects of the interface while still using Allegro to handle input from the mouse, keyboard, joystick, etc.

A GUI dialog is stored as an array of DIALOG objects, each one containing the fields:

typedef struct DIALOG
   int (*proc)(int, DIALOG *, int); - dialog procedure (message handler)
   int x, y, w, h;                  - position and size of the object
   int fg, bg;                      - foreground and background colors
   int key;                         - ASCII keyboard shortcut
   int flags;                       - flags about the status of
                                      the object
   int d1, d2;                      - whatever you want to use them for
   void *dp, *dp2, *dp3;            - pointers to more
                                      object-specific data

The array should end with an object which has the proc pointer set to NULL.

The flags field may contain any combination of the bit flags:

   D_EXIT          - this object should close the dialog when it is clicked
   D_SELECTED      - this object is selected
   D_GOTFOCUS      - this object has got the input focus
   D_GOTMOUSE      - the mouse is currently on top of this object
   D_HIDDEN        - this object is hidden and inactive
   D_DISABLED      - this object is greyed-out and inactive
   D_DIRTY         - this object needs to be redrawn
   D_INTERNAL      - don't use this! It is for internal use by the
   D_USER          - any powers of two above this are free for your own use

Each object is controlled by a dialog procedure, which is stored in the proc pointer. This will be called by the dialog manager whenever any action concerning the object is required, or you can call it directly with the object_message() function. The dialog procedure should follow the form:

   int foo(int msg, DIALOG *d, int c);

It will be passed a flag (msg) indicating what action it should perform, a pointer to the object concerned (d), and if msg is MSG_CHAR or MSG_XCHAR, the key that was pressed (c). Note that d is a pointer to a specific object, and not to the entire dialog.

The dialog procedure should return one of the values:

   D_O_K          - normal return status
   D_CLOSE        - tells the dialog manager to close the dialog
   D_REDRAW       - tells the dialog manager to redraw the entire dialog
   D_REDRAWME     - tells the dialog manager to redraw the current object
   D_WANTFOCUS    - requests that the input focus be given to this object
   D_USED_CHAR    - MSG_CHAR and MSG_XCHAR return this if they used the key

Dialog procedures may be called with any of the messages:

Tells the object to initialise itself. The dialog manager sends this to all the objects in a dialog just before it displays the dialog.

Sent to all objects when closing a dialog, allowing them to perform whatever cleanup operations they require.

Tells the object to draw itself onto the screen. The mouse pointer will be turned off when this message is sent, so the drawing code does not need to worry about it.

Informs the object that a mouse button has been clicked while the mouse was on top of the object. Typically an object will perform its own mouse tracking as long as the button is held down, and only return from this message handler when it is released.

Sent when the user double-clicks on an object. A MSG_CLICK will be sent when the button is first pressed, then MSG_DCLICK if it is released and pressed again within a short space of time.

Sent when the keyboard shortcut for the object is pressed, or if enter, space, or a joystick button is pressed while it has the input focus.

When a key is pressed, this message is sent to the object that has the input focus, with a readkey() format character code (ASCII value in the low byte, scancode in the high byte) as the c parameter. If the object deals with the keypress it should return D_USED_CHAR, otherwise it should return D_O_K to allow the default keyboard interface to operate. If you need to access Unicode character input, you should use MSG_UCHAR instead of MSG_CHAR.

If an object ignores the MSG_CHAR input, this message will be sent immediately after it, passed the full Unicode key value as the c parameter. This enables you to read character codes greater than 255, but cannot tell you anything about the scancode: if you need to know that, use MSG_CHAR instead. This handler should return D_USED_CHAR if it processed the input, or D_O_K otherwise.

When a key is pressed, Allegro will send a MSG_CHAR and MSG_UCHAR to the object with the input focus. If this object doesn't process the key (ie. it returns D_O_K rather than D_USED_CHAR), the dialog manager will look for an object with a matching keyboard shortcut in the key field, and send it a MSG_KEY. If this fails, it broadcasts a MSG_XCHAR to all objects in the dialog, allowing them to respond to special keypresses even when they don't have the input focus. Normally you should ignore this message (return D_O_K rather than D_USED_CHAR), in which case Allegro will perform default actions such as moving the focus in response to the arrow keys and closing the dialog if ESC is pressed.

Queries whether an object is willing to accept the input focus. It should return D_WANTFOCUS if it does, or D_O_K if it isn't interested in getting user input.

Sent whenever an object gains or loses the input focus. These messages will always be followed by a MSG_DRAW, to let objects display themselves differently when they have the input focus. If you return D_WANTFOCUS in response to a MSG_LOSTFOCUS event, this will prevent your object from losing the focus when the mouse moves off it onto the screen background or some inert object, so it will only lose the input focus when some other object is ready to take over the focus (this trick is used by the d_edit_proc() object).

Sent when the mouse moves on top of or away from an object. Unlike the focus messages, these are not followed by a MSG_DRAW, so if the object is displayed differently when the mouse is on top of it, it is responsible for redrawing itself in response to these messages.

Sent whenever the dialog manager has nothing better to do.

Sent by radio button objects to deselect other buttons in the same group when they are clicked. The group number is passed in the c message parameter.

Sent to the focused object whenever the mouse wheel moves. The c message parameter contains the number of clicks.

Sent when the corresponding mouse button is pressed.

Sent when the corresponding mouse button is released.

The first free message value. Any numbers from here on (MSG_USER, MSG_USER+1, MSG_USER+2, ... MSG_USER+n) are free to use for whatever you like.

Allegro provides several standard dialog procedures. You can use these as they are to provide simple user interface objects, or you can call them from within your own dialog procedures, resulting in a kind of OOP inheritance. For instance, you could make an object which calls d_button_proc to draw itself, but handles the click message in a different way, or an object which calls d_button_proc for everything except drawing itself, so it would behave like a normal button but could look completely different.

Since the release of Allegro version 3.9.33 (CVS), some GUI objects and menus are being drawn differently unlike in previous Allegro versions. The changes are the following:

int d_clear_proc(int msg, DIALOG *d, int c);
This just clears the screen when it is drawn. Useful as the first object in a dialog.

int d_box_proc(int msg, DIALOG *d, int c);
int d_shadow_box_proc(int msg, DIALOG *d, int c);
These draw boxes onto the screen, with or without a shadow.

int d_bitmap_proc(int msg, DIALOG *d, int c);
This draws a bitmap onto the screen, which should be pointed to by the dp field.

int d_text_proc(int msg, DIALOG *d, int c);
int d_ctext_proc(int msg, DIALOG *d, int c);
int d_rtext_proc(int msg, DIALOG *d, int c);
These draw text onto the screen. The dp field should point to the string to display. d_ctext_proc() centres the string around the x coordinate, and d_rtext_proc() right aligns it. Any '&' characters in the string will be replaced with lines underneath the following character, for displaying keyboard shortcuts (as in MS Windows). To display a single ampersand, put "&&". To draw the text in something other than the default font, set the dp2 field to point to your custom font data.

int d_button_proc(int msg, DIALOG *d, int c);
A button object (the dp field points to the text string). This object can be selected by clicking on it with the mouse or by pressing its keyboard shortcut. If the D_EXIT flag is set, selecting it will close the dialog, otherwise it will toggle on and off. Like d_text_proc(), ampersands can be used to display the keyboard shortcut of the button.

int d_check_proc(int msg, DIALOG *d, int c);
This is an example of how you can derive objects from other objects. Most of the functionality comes from d_button_proc(), but it displays itself as a check box. If the d1 field is non-zero, the text will be printed to the right of the check, otherwise it will be on the left.

Note: the object width should allow space for the text as well as the check box (which is square, with sides equal to the object height).

int d_radio_proc(int msg, DIALOG *d, int c);
A radio button object. A dialog can contain any number of radio button groups: selecting a radio button causes other buttons within the same group to be deselected. The dp field points to the text string, d1 specifies the group number, and d2 is the button style (0=circle, 1=square).

int d_icon_proc(int msg, DIALOG *d, int c);
A bitmap button. The fg color is used for the dotted line showing focus, and the bg color for the shadow used to fill in the top and left sides of the button when "pressed". d1 is the "push depth", ie. the number of pixels the icon will be shifted to the right and down when selected (default 2) if there is no "selected" image. d2 is the distance by which the dotted line showing focus is indented (default 2). dp points to a bitmap for the icon, while dp2 and dp3 are the selected and disabled images respectively (optional, may be NULL).

int d_keyboard_proc(int msg, DIALOG *d, int c);
This is an invisible object for implementing keyboard shortcuts. You can put an ASCII code in the key field of the dialog object (a character such as 'a' to respond to a simple keypress, or a number 1-26 to respond to a control key a-z), or you can put a keyboard scancode in the d1 and/or d2 fields. When one of these keys is pressed, the object will call the function pointed to by dp. This should return an int, which will be passed back to the dialog manager, so it can return D_O_K, D_REDRAW, D_CLOSE, etc.

int d_edit_proc(int msg, DIALOG *d, int c);
An editable text object (the dp field points to the string). When it has the input focus (obtained by clicking on it with the mouse), text can be typed into this object. The d1 field specifies the maximum number of characters that it will accept, and d2 is the text cursor position within the string.

int d_list_proc(int msg, DIALOG *d, int c);
A list box object. This will allow the user to scroll through a list of items and to select one by clicking or with the arrow keys. If the D_EXIT flag is set, double clicking on a list item will close the dialog. The index of the selected item is held in the d1 field, and d2 is used to store how far it has scrolled through the list. The dp field points to a function which will be called to obtain information about the contents of the list. This should follow the form:

      char *foobar(int index, int *list_size);

If index is zero or positive, the function should return a pointer to the string which is to be displayed at position index in the list. If index is negative, it should return NULL and list_size should be set to the number of items in the list.

To create a multiple selection listbox, set the dp2 field to an array of byte flags indicating the selection state of each list item (non-zero for selected entries). This table must be at least as big as the number of objects in the list!

int d_text_list_proc(int msg, DIALOG *d, int c);
Like d_list_proc, but allows the user to type in the first few characters of a listbox entry in order to select it. Uses dp3 internally, so you mustn't store anything important there yourself.

int d_textbox_proc(int msg, DIALOG *d, int c);
A text box object. The dp field points to the text which is to be displayed in the box. If the text is long, there will be a vertical scrollbar on the right hand side of the object which can be used to scroll through the text. The default is to print the text with word wrapping, but if the D_SELECTED flag is set, the text will be printed with character wrapping. The d1 field is used internally to store the number of lines of text, and d2 is used to store how far it has scrolled through the text.

int d_slider_proc(int msg, DIALOG *d, int c);
A slider control object. This object holds a value in d2, in the range from 0 to d1. It will display as a vertical slider if h is greater than or equal to w, otherwise it will display as a horizontal slider. The dp field can contain an optional bitmap to use for the slider handle, and dp2 can contain an optional callback function, which is called each time d2 changes. The callback function should have the following prototype:

      int function(void *dp3, int d2);

The d_slider_proc object will return the value of the callback function.

int d_menu_proc(int msg, DIALOG *d, int c);
This object is a menu bar which will drop down child menus when it is clicked or if an alt+key corresponding to one of the shortcuts in the menu is pressed. It ignores a lot of the fields in the dialog structure, in particular the color is taken from the gui_*_color variables, and the width and height are calculated automatically (the w and h fields from the DIALOG are only used as a minimum size.) The dp field points to an array of menu structures: see do_menu() for more information. The top level menu will be displayed as a horizontal bar, but when child menus drop down from it they will be in the normal vertical format used by do_menu(). When a menu item is selected, the return value from the menu callback function is passed back to the dialog manager, so your callbacks should return D_O_K, D_REDRAW, or D_CLOSE.

int d_yield_proc(int msg, DIALOG *d, int c);
An invisible helper object that yields timeslices for the scheduler (if the system supports it) when the gui has nothing to do but waiting for user actions. You should put one instance of this object in each dialog array because it may be needed on systems with an unusual scheduling algorithm (for instance QNX) in order to make the GUI fully responsive.

The behaviour of the dialog manager can be controlled by the variables:

extern int gui_mouse_focus;
If set, the input focus follows the mouse pointer around the dialog, otherwise a click is required to move it.

extern int gui_fg_color;
extern int gui_bg_color;
The foreground and background colors for the standard dialogs (alerts, menus, and the file selector). They default to 255 and 0.

extern int gui_mg_color;
The color used for displaying greyed-out dialog objects (with the D_DISABLED flag set). Defaults to 8.

extern int gui_font_baseline;
If set to a non-zero value, adjusts the keyboard shortcut underscores to account for the height of the descenders in your font.

extern int (*gui_mouse_x)();
extern int (*gui_mouse_y)();
extern int (*gui_mouse_z)();
extern int (*gui_mouse_b)();
Hook functions, used by the GUI routines whenever they need to access the mouse state. By default these just return copies of the mouse_x, mouse_y, mouse_z, and mouse_b variables, but they could be used to offset or scale the mouse position, or read input from a different source entirely.

You can change the global 'font' pointer to make the GUI objects use something other than the standard 8x8 font. The standard dialog procedures, menus, and alert boxes, will work with fonts of any size, but the gfx_mode_select() dialog will look wrong with anything other than 8x8 fonts.

int gui_textout(BITMAP *bmp, const char *s, int x, y, color, centre);
Helper function for use by the GUI routines. Draws a text string onto the screen, interpreting the '&' character as an underbar for displaying keyboard shortcuts. Returns the width of the output string in pixels.

int gui_strlen(const char *s);
Helper function for use by the GUI routines. Returns the length of a string in pixels, ignoring '&' characters.

void position_dialog(DIALOG *dialog, int x, int y);
Moves an array of dialog objects to the specified screen position (specified as the top left corner of the dialog).

void centre_dialog(DIALOG *dialog);
Moves an array of dialog objects so that it is centered in the screen.

void set_dialog_color(DIALOG *dialog, int fg, int bg);
Sets the foreground and background colors of an array of dialog objects.

int find_dialog_focus(DIALOG *dialog);
Searches the dialog for the object which has the input focus, returning an index or -1 if the focus is not set. This is useful if you are calling do_dialog() several times in a row and want to leave the focus in the same place it was when the dialog was last displayed, as you can call do_dialog(dlg, find_dialog_focus(dlg));

int offer_focus(DIALOG *d, int obj, int *focus_obj, int force);
Offers the input focus to a particular object. Normally the function sends the MSG_WANTFOCUS message to query whether the object is willing to accept the focus. However, passing any non zero value as force argument instructs the function to authoritatively set the focus to the object.

int object_message(DIALOG *dialog, int msg, int c);
Sends a message to an object and returns the answer it has generated. Remember that the first parameter is the dialog object (not a whole array) that you wish to send the message to. For example, to make the second object in a dialog draw itself, you might write:

      object_message(&dialog[1], MSG_DRAW, 0);

int dialog_message(DIALOG *dialog, int msg, int c, int *obj);
Sends a message to all the objects in an array. If any of the dialog procedures return values other than D_O_K, it returns the value and sets obj to the index of the object which produced it.

int broadcast_dialog_message(int msg, int c);
Broadcasts a message to all the objects in the active dialog. If any of the dialog procedures return values other than D_O_K, it returns that value.

int do_dialog(DIALOG *dialog, int focus_obj);
The basic dialog manager function. This displays a dialog (an array of dialog objects, terminated by one with a NULL dialog procedure), and sets the input focus to the focus_obj (-1 if you don't want anything to have the focus). It interprets user input and dispatches messages as they are required, until one of the dialog procedures tells it to close the dialog, at which point it returns the index of the object that caused it to exit.

int popup_dialog(DIALOG *dialog, int focus_obj);
Like do_dialog(), but it stores the data on the screen before drawing the dialog and restores it when the dialog is closed. The screen area to be stored is calculated from the dimensions of the first object in the dialog, so all the other objects should lie within this one.

DIALOG_PLAYER *init_dialog(DIALOG *dialog, int focus_obj);
This function provides lower level access to the same functionality as do_dialog(), but allows you to combine a dialog box with your own program control structures. It initialises a dialog, returning a pointer to a player object that can be used with update_dialog() and shutdown_dialog(). With these functions, you could implement your own version of do_dialog() with the lines:

      DIALOG_PLAYER *player = init_dialog(dialog, focus_obj);

while (update_dialog(player)) ;

return shutdown_dialog(player);

int update_dialog(DIALOG_PLAYER *player);
Updates the status of a dialog object returned by init_dialog(). Returns TRUE if the dialog is still active, or FALSE if it has terminated. Upon a return value of FALSE, it is up to you whether to call shutdown_dialog() or to continue execution. The object that requested the exit can be determined from the player->obj field.

int shutdown_dialog(DIALOG_PLAYER *player);
Destroys a dialog player object returned by init_dialog(), returning the object that caused it to exit (this is the same as the return value from do_dialog()).

extern DIALOG *active_dialog;
Global pointer to the most recent activated dialog. This may be useful if an object needs to iterate through a list of all its siblings.

Popup or pulldown menus are created as an array of the structures:

typedef struct MENU
   char *text;                   - the text to display for the menu item
   int (*proc)(void);            - called when the menu item is clicked
   struct MENU *child;           - nested child menu
   int flags;                    - disabled or checked state
   void *dp;                     - pointer to any data you need

Each menu item contains a text string. This can use the '&' character to indicate keyboard shortcuts, or can be an zero-length string to display the item as a non-selectable splitter bar. If the string contains a "\t" tab character, any text after this will be right-justified, eg. for displaying keyboard shortcut information. The proc pointer is a function which will be called when the menu item is selected, and child points to another menu, allowing you to create nested menus. Both proc and child may be NULL. The proc function returns an integer which is ignored if the menu was brought up by calling do_menu(), but which is passed back to the dialog manager if it was created by a d_menu_proc() object. The array of menu items is terminated by an entry with a NULL text pointer.

Menu items can be disabled (greyed-out) by setting the D_DISABLED bit in the flags field, and a check mark can be displayed next to them by setting the D_SELECTED bit. With the default alignment and font this will usually overlap the menu text, so if you are going to use checked menu items it would be a good idea to prefix all your options with a space or two, to ensure there is room for the check.

int do_menu(MENU *menu, int x, int y)
Displays and animates a popup menu at the specified screen coordinates (these will be adjusted if the menu does not entirely fit on the screen). Returns the index of the menu item that was selected, or -1 if the menu was cancelled. Note that the return value cannot indicate selection from child menus, so you will have to use the callback functions if you want multi-level menus.

extern MENU *active_menu;
When a menu callback procedure is triggered, this will be set to the menu item that was selected, so your routine can determine where it was called from.

extern void (*gui_menu_draw_menu)(int x, int y, int w, int h);
extern void (*gui_menu_draw_menu_item)(MENU *m, int x, int y, int w, int h, int bar, int sel);
If set, these functions will be called whenever a menu needs to be drawn, so you can change how menus look.

gui_menu_draw_menu() is passed the position and size of the menu. It should draw the background of the menu onto screen.

gui_menu_draw_menu_item() is called once for each menu item that is to be drawn. bar will be set if the item is part of a top-level horizontal menu bar, and sel will be set if the menu item is selected. It should also draw onto screen.

int alert(const char *s1, *s2, *s3, const char *b1, *b2, int c1, c2);
Displays a popup alert box, containing three lines of text (s1-s3), and with either one or two buttons. The text for these buttons is passed in b1 and b2 (b2 may be NULL), and the keyboard shortcuts in c1 and c2. Returns 1 or 2 depending on which button was clicked. If the alert is dismissed by pressing ESC when ESC is not one of the keyboard shortcuts, it treats it as a click on the second button (this is consistent with the common "Ok", "Cancel" alert).

int alert3(const char *s1, *s2, *s3, const char *b1, *b2, *b3, int c1, c2, c3);
Like alert(), but with three buttons. Returns 1, 2, or 3.

int file_select(const char *message, char *path, const char *ext);
Deprecated. Use file_select_ex() instead, passing the two constants OLD_FILESEL_WIDTH and OLD_FILESEL_HEIGHT if you want the file selector to be displayed with the dimensions of the old file selector.

int file_select_ex(const char *message, char *path, const char *ext, int size, int w, int h);
Displays the Allegro file selector, with the message as caption. The path parameter contains the initial filename to display (this can be used to set the starting directory, or to provide a default filename for a save-as operation). The user selection is returned by altering the path buffer, whose maximum capacity in bytes is specified by the size parameter. Note that it should have room for at least 80 characters (not bytes), so you should reserve 6x that amount, just to be sure. The list of files is filtered according to the file extensions in the ext parameter. Passing NULL includes all files; "PCX;BMP" includes only files with .PCX or .BMP extensions. If you wish to control files by their attributes, one of the fields in the extension list can begin with a slash, followed by a set of attribute characters. Any attributes written on their own, or with a + before them, indicate to include only files which have that attribute set. Any attributes with a '-' before them indicate to leave out any files with that attribute. The flag characters are 'r' (read-only), 'h' (hidden), 's' (system), 'd' (directory), and 'a' (archive). For example, an extension string of "PCX;BMP;/+r-d" will display only PCX or BMP files that are read-only, and no directories. The file selector is stretched to the width and height specified in the w and h parameters, and to the size of the standard Allegro font. If either the width or height argument is set to zero, it is stretched to the corresponding screen dimension. This function returns zero if it was closed with the Cancel button or non-zero if it was OK'd.

int gfx_mode_select(int *card, int *w, int *h);
Displays the Allegro graphics mode selection dialog, which allows the user to select a screen mode and graphics card. Stores the selection in the three variables, and returns zero if it was closed with the Cancel button or non-zero if it was OK'd.

int gfx_mode_select_ex(int *card, int *w, int *h, int *color_depth);
Extended version of the graphics mode selection dialog, which allows the user to select the color depth as well as the resolution and hardware driver. This version of the function reads the initial values from the parameters when it activates, so you can specify the default values.

extern int (*gui_shadow_box_proc)(int msg, struct DIALOG *d, int c);
extern int (*gui_ctext_proc)(int msg, struct DIALOG *d, int c);
extern int (*gui_button_proc)(int msg, struct DIALOG *d, int c);
extern int (*gui_edit_proc)(int msg, struct DIALOG *d, int c);
extern int (*gui_list_proc)(int msg, struct DIALOG *d, int c);
extern int (*gui_text_list_proc)(int msg, struct DIALOG *d, int c);
If set, these functions will be used by the standard Allegro dialogs. This allows you to customise the look and feel, much like gui_fg_color and gui_bg_color, but much more flexiblely.

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