The '' Program

The ProXL source code file listed below encapsulates all of the concepts presented in the previous session as a single program. This program appears in the file demo('').

:- module(proxl_hello, [hello/0]). :- use_module(library(proxl)). % hello % test program for message_window/7. hello :- chosen_font(Fontspec), current_font(Fontspec, Fontname), !, message_window('Hello, world!!', Fontname, goldenrod, forestgreen, cyan, black, _). % message_window(+Message, +Fontname, +Bg1, +Bg2, +Letters, +Shadow, % -Window) % Window is a window with Message, a Prolog atom, centered in it % in Fontname, an atom naming a font. Bg1, Bg2, Letters and Shadow % are atoms naming colors. message_window(Message, Fontname, Bg1, Bg2, Letters, Shadow, Window) :- load_font(Fontname, Font), message_size(Message, Font, Window_width, Window_height, Xoffset, Yoffset, Xdisplacement, Ydisplacement), alloc_color(Letters, Letters_pix), alloc_color(Shadow, Shadow_pix), background_pixmap(Bg1, Bg2, Bg), create_cursor(gumby, Cursor), create_window(Window, [ size(Window_width,Window_height), mapped(true), border_width(2), background(Bg), cursor(Cursor), property('WM_NAME', hello), callback(expose, [count(0)], expose_message(Window,Message,Letters_pix, Shadow_pix,Xoffset,Yoffset, Xdisplacement,Ydisplacement)), callback(button_press, [], destroy_window(Window)) ], [font(Font)]).
% message_size(+Message, +Font, -Window_width, -Window_height, -Xoffset, % -Yoffset, -Xdisplacement, -Ydisplacement) % Window_width and Window_height are the size of the smallest window % that will accomodate Message drawn with a drop shadow using font % Font. Xoffset and Yoffset are the offset from the center of the % window at which we want to draw the string. Since we want to keep % the message centered even when the window is resized, it's most % convenient to remember the offset from the center of the window, % which won't change. Xdisplacement and Ydisplacement are the % distance the shadow should be displaced from the primary image, % computed as 1/5 of the font width and height, respectively. message_size(Message, Font, Window_width, Window_height, Xoffset, Yoffset, Xdisplacement, Ydisplacement) :- get_font_attributes(Font, [height(Hei), max_width(Wid)]), Xdisplacement is Wid//5, Ydisplacement is Hei//5, text_extents(Font, Message, Lbearing, Rbearing, _, Asc, Desc), Xoffset is Lbearing-(Lbearing+Rbearing+Xdisplacement)//2, Yoffset is Asc-(Asc+Desc+Ydisplacement)//2, % X and Y offset Window_width is Lbearing+Rbearing+Xdisplacement+4, Window_height is Asc+Desc+Ydisplacement+4. % background_pixmap(+Bg1, +Bg2, -Pixmap) % Pixmap is a newly allocated 4x4 background pixmap filled with our % background pattern. Bg1 and Bg2 are the names of the colors to % use for this pixmap. background_pixmap(Bg1, Bg2, Pixmap) :- alloc_color(Bg1, Bg1_pix), alloc_color(Bg2, Bg2_pix), create_pixmap(Pixmap, [size(4,4)], [foreground(Bg1_pix)]), fill_rectangle(Pixmap, 0, 0, 3, 3), put_graphics_attributes(Pixmap, [foreground(Bg2_pix)]), draw_segments(Pixmap, [segment(0,0,3,3),segment(0,3,3,0)]).
% expose_message(+Window, +Message, +Letters_pix, +Shadow_pix, % +Xoffset, +Yoffset, +Xdisplacement, +Ydisplacement) % Redisplay the contents of Window. Window is a window created by % message_window/7, and Message is the message displayed in it. % Letters_pix and Shadow_pix are the pixel values to draw the % letters and shadow in, respectively. Xoffset and Yoffset are % the pixel offset from the center of the window at which Message % should be drawn. And Xdisplacement and Ydisplacement are the % pixel offset from the message at which the shadow should be drawn. expose_message(Window, Message, Letters_pix, Shadow_pix, Xoffset, Yoffset, Xdisplacement, Ydisplacement) :- get_window_attributes(Window, [size(Width,Height)]), X is Width//2 + Xoffset, % compute position for message Y is Height//2 + Yoffset, Shadow_x is X+Xdisplacement, Shadow_y is Y+Ydisplacement, clear_window(Window), put_graphics_attributes(Window, [foreground(Shadow_pix)]), draw_string(Window, Shadow_x, Shadow_y, Message), put_graphics_attributes(Window, [foreground(Letters_pix)]), draw_string(Window, X, Y, Message). % chosen_font(-Fontname) % table of fonts to try. chosen_font('*-times-bold-i-*-24-*'). % First choice, for X11R3 chosen_font('vgb-25'). % Second coice, or on X11R2 chosen_font('fixed'). % Last choice ... % user:runtime_entry(+Context) % The main program for runtime systems. user:runtime_entry(start) :- hello, handle_events. % process callbacks till % hello window is destroyed