X11 demo in Felix

x11.fpc

Description: Linux X11 support
requires_dlibs: -lX11
requires_slibs: -lX11

x11_app.flx

export requires header "#include <X11/Xlib.h>", package "x11";

cproc HandleEvents(width:int, height:int) = {
    println$ "In Felix: width: " + width.str + " height: " + height.str;
}

proc init_x11() = { cstmt """
    Display                 *display;
    Visual                  *visual;
    int                     depth;
    int                     text_x;
    int                     text_y;
    XSetWindowAttributes    frame_attributes;
    Window                  frame_window;
    XFontStruct             *fontinfo;
    XGCValues               gr_values;
    GC                      graphical_context;
    XKeyEvent               event;
    char                    hello_string[] = "Hello World From Felix";
    int                     hello_string_length = strlen(hello_string);

    display = XOpenDisplay(NULL);
    visual = DefaultVisual(display, 0);
    depth  = DefaultDepth(display, 0);
    
    frame_attributes.background_pixel = XWhitePixel(display, 0);
    /* create the application window */
    frame_window = XCreateWindow(display, XRootWindow(display, 0),
                                 0, 0, 400, 400, 5, depth,
                                 InputOutput, visual, CWBackPixel,
                                 &frame_attributes);
    XStoreName(display, frame_window, "Hello World Example");
    XSelectInput(display, frame_window, ExposureMask | StructureNotifyMask);

    fontinfo = XLoadQueryFont(display, "10x20");
    gr_values.font = fontinfo->fid;
    gr_values.foreground = XBlackPixel(display, 0);
    graphical_context = XCreateGC(display, frame_window, 
                                  GCFont+GCForeground, &gr_values);
    XMapWindow(display, frame_window);

    while ( 1 ) {
        XNextEvent(display, (XEvent *)&event);
        switch ( event.type ) {
            case Expose:
            {
                XWindowAttributes window_attributes;
                int font_direction, font_ascent, font_descent;
                XCharStruct text_structure;
                XTextExtents(fontinfo, hello_string, hello_string_length, 
                             &font_direction, &font_ascent, &font_descent, 
                             &text_structure);
                XGetWindowAttributes(display, frame_window, &window_attributes);

                // call our felix procedure
                $1(window_attributes.width, window_attributes.height);

                text_x = (window_attributes.width - text_structure.width)/2;
                text_y = (window_attributes.height - 
                          (text_structure.ascent+text_structure.descent))/2;
                XDrawString(display, frame_window, graphical_context,
                            text_x, text_y, hello_string, hello_string_length);
                break;
            }
            default:
                break;
        }
    }
    """ HandleEvents;
}

init_x11();

Note, the HandleEvents procedure is passed into the C++ code via substitution on line 57.