emccpre.js

/*
 * emccpre.js: one of the Javascript components of an Emscripten-based
 * web/Javascript front end for Puzzles.
 *
 * The other parts of this system live in emcc.c and emcclib.js. It
 * also depends on being run in the context of a web page containing
 * an appropriate collection of bits and pieces (a canvas, some
 * buttons and links etc), which is generated for each puzzle by the
 * script html/jspage.pl.
 *
 * This file contains the Javascript code which is prefixed unmodified
 * to Emscripten's output via the --pre-js option. It declares all our
 * global variables, and provides the puzzle init function and a
 * couple of other helper functions.
 */

// To avoid flicker while doing complicated drawing, we use two
// canvases, the same size. One is actually on the web page, and the
// other is off-screen. We do all our drawing on the off-screen one
// first, and then copy rectangles of it to the on-screen canvas in
// response to draw_update() calls by the game backend.
var onscreen_canvas, offscreen_canvas;

// A persistent drawing context for the offscreen canvas, to save
// constructing one per individual graphics operation.
var ctx;

// Bounding rectangle for the copy to the onscreen canvas that will be
// done at drawing end time. Updated by js_canvas_draw_update and used
// by js_canvas_end_draw.
var update_xmin, update_xmax, update_ymin, update_ymax;

// Module object for Emscripten. We fill in these parameters to ensure
// that Module.run() won't be called until we're ready (we want to do
// our own init stuff first), and that when main() returns nothing
// will get cleaned up so we remain able to call the puzzle's various
// callbacks.
var Module = {
    'noInitialRun': true,
    'noExitRuntime': true
};

// Variables used by js_canvas_find_font_midpoint().
var midpoint_test_str = "ABCDEFGHIKLMNOPRSTUVWXYZ0123456789";
var midpoint_cache = [];

// Variables used by js_activate_timer() and js_deactivate_timer().
var timer = null;
var timer_reference_date;

// void timer_callback(double tplus);
//
// Called every 20ms while timing is active.
var timer_callback;

// The status bar object, if we create one.
var statusbar = null;

// Currently live blitters. We keep an integer id for each one on the
// JS side; the C side, which expects a blitter to look like a struct,
// simply defines the struct to contain that integer id.
var blittercount = 0;
var blitters = [];

// State for the dialog-box mechanism. dlg_dimmer and dlg_form are the
// page-darkening overlay and the actual dialog box respectively;
// dlg_next_id is used to allocate each checkbox a unique id to use
// for linking its label to it (see js_dialog_boolean);
// dlg_return_funcs is a list of JS functions to be called when the OK
// button is pressed, to pass the results back to C.
var dlg_dimmer = null, dlg_form = null;
var dlg_next_id = 0;
var dlg_return_funcs = null;

// void dlg_return_sval(int index, const char *val);
// void dlg_return_ival(int index, int val);
//
// C-side entry points called by functions in dlg_return_funcs, to
// pass back the final value in each dialog control.
var dlg_return_sval, dlg_return_ival;

// The <select> object implementing the game-type drop-down, and a
// list of the <option> objects inside it. Used by js_add_preset(),
// js_get_selected_preset() and js_select_preset().
//
// gametypethiscustom is an option which indicates some custom game
// params you've already set up, and which will be auto-selected on
// return from the customisation dialog; gametypenewcustom is an
// option which you select to indicate that you want to bring up the
// customisation dialog and select a new configuration. Ideally I'd do
// this with just one option serving both purposes, but instead we
// have to do this a bit oddly because browsers don't send 'onchange'
// events for a select element if you reselect the same one - so if
// you've picked a custom setup and now want to change it, you need a
// way to specify that.
var gametypeselector = null, gametypeoptions = [];
var gametypethiscustom = null, gametypehiddencustom = null;

// The two anchors used to give permalinks to the current puzzle. Used
// by js_update_permalinks().
var permalink_seed, permalink_desc;

// The undo and redo buttons. Used by js_enable_undo_redo().
var undo_button, redo_button;

// A div element enclosing both the puzzle and its status bar, used
// for positioning the resize handle.
var resizable_div;

// Helper function to find the absolute position of a given DOM
// element on a page, by iterating upwards through the DOM finding
// each element's offset from its parent, and thus calculating the
// page-relative position of the target element.
function element_coords(element) {
    var ex = 0, ey = 0;
    while (element.offsetParent) {
        ex += element.offsetLeft;
        ey += element.offsetTop;
        element = element.offsetParent;
    }
    return {x: ex, y:ey};
}

// Helper function which is passed a mouse event object and a DOM
// element, and returns the coordinates of the mouse event relative to
// the top left corner of the element by subtracting element_coords
// from event.page{X,Y}.
function relative_mouse_coords(event, element) {
    var ecoords = element_coords(element);
    return {x: event.pageX - ecoords.x,
            y: event.pageY - ecoords.y};
}

// Init function called from body.onload.
function initPuzzle() {
    // Construct the off-screen canvas used for double buffering.
    onscreen_canvas = document.getElementById("puzzlecanvas");
    offscreen_canvas = document.createElement("canvas");
    offscreen_canvas.width = onscreen_canvas.width;
    offscreen_canvas.height = onscreen_canvas.height;

    // Stop right-clicks on the puzzle from popping up a context menu.
    // We need those right-clicks!
    onscreen_canvas.oncontextmenu = function(event) { return false; }

    // Set up mouse handlers. We do a bit of tracking of the currently
    // pressed mouse buttons, to avoid sending mousemoves with no
    // button down (our puzzles don't want those events).
    mousedown = Module.cwrap('mousedown', 'void',
                             ['number', 'number', 'number']);
    buttons_down = 0;
    onscreen_canvas.onmousedown = function(event) {
        var xy = relative_mouse_coords(event, onscreen_canvas);
        mousedown(xy.x, xy.y, event.button);
        buttons_down |= 1 << event.button;
        onscreen_canvas.setCapture(true);
    };
    mousemove = Module.cwrap('mousemove', 'void',
                             ['number', 'number', 'number']);
    onscreen_canvas.onmousemove = function(event) {
        if (buttons_down) {
            var xy = relative_mouse_coords(event, onscreen_canvas);
            mousemove(xy.x, xy.y, buttons_down);
        }
    };
    mouseup = Module.cwrap('mouseup', 'void',
                           ['number', 'number', 'number']);
    onscreen_canvas.onmouseup = function(event) {
        if (buttons_down & (1 << event.button)) {
            buttons_down ^= 1 << event.button;
            var xy = relative_mouse_coords(event, onscreen_canvas);
            mouseup(xy.x, xy.y, event.button);
        }
    };

    // Set up keyboard handlers. We do all the actual keyboard
    // handling in onkeydown; but we also call event.preventDefault()
    // in both the keydown and keypress handlers. This means that
    // while the canvas itself has focus, _all_ keypresses go only to
    // the puzzle - so users of this puzzle collection in other media
    // can indulge their instinct to press ^R for redo, for example,
    // without accidentally reloading the page.
    key = Module.cwrap('key', 'void', ['number', 'number', 'string',
                                       'string', 'number', 'number']);
    onscreen_canvas.onkeydown = function(event) {
        key(event.keyCode, event.charCode, event.key, event.char,
            event.shiftKey ? 1 : 0, event.ctrlKey ? 1 : 0);
        event.preventDefault();
    };
    onscreen_canvas.onkeypress = function(event) {
        event.preventDefault();
    };

    // command() is a C function called to pass back events which
    // don't fall into other categories like mouse and key events.
    // Mostly those are button presses, but there's also one for the
    // game-type dropdown having been changed.
    command = Module.cwrap('command', 'void', ['number']);

    // Event handlers for buttons and things, which call command().
    document.getElementById("specific").onclick = function(event) {
        // Ensure we don't accidentally process these events when a
        // dialog is actually active, e.g. because the button still
        // has keyboard focus
        if (dlg_dimmer === null)
            command(0);
    };
    document.getElementById("random").onclick = function(event) {
        if (dlg_dimmer === null)
            command(1);
    };
    document.getElementById("new").onclick = function(event) {
        if (dlg_dimmer === null)
            command(5);
    };
    document.getElementById("restart").onclick = function(event) {
        if (dlg_dimmer === null)
            command(6);
    };
    undo_button = document.getElementById("undo");
    undo_button.onclick = function(event) {
        if (dlg_dimmer === null)
            command(7);
    };
    redo_button = document.getElementById("redo");
    redo_button.onclick = function(event) {
        if (dlg_dimmer === null)
            command(8);
    };
    document.getElementById("solve").onclick = function(event) {
        if (dlg_dimmer === null)
            command(9);
    };

    gametypeselector = document.getElementById("gametype");
    gametypeselector.onchange = function(event) {
        if (dlg_dimmer === null)
            command(2);
    };

    // In IE, the canvas doesn't automatically gain focus on a mouse
    // click, so make sure it does
    onscreen_canvas.addEventListener("mousedown", function(event) {
        onscreen_canvas.focus();
    });

    // In our dialog boxes, Return and Escape should be like pressing
    // OK and Cancel respectively
    document.addEventListener("keydown", function(event) {

        if (dlg_dimmer !== null && event.keyCode == 13) {
            for (var i in dlg_return_funcs)
                dlg_return_funcs[i]();
            command(3);
        }

        if (dlg_dimmer !== null && event.keyCode == 27)
            command(4);
    });

    // Set up the function pointers we haven't already grabbed. 
    dlg_return_sval = Module.cwrap('dlg_return_sval', 'void',
                                   ['number','string']);
    dlg_return_ival = Module.cwrap('dlg_return_ival', 'void',
                                   ['number','number']);
    timer_callback = Module.cwrap('timer_callback', 'void', ['number']);

    // Save references to the two permalinks.
    permalink_desc = document.getElementById("permalink-desc");
    permalink_seed = document.getElementById("permalink-seed");

    // Default to giving keyboard focus to the puzzle.
    onscreen_canvas.focus();

    // Create the resize handle.
    var resize_handle = document.createElement("canvas");
    resize_handle.width = 10;
    resize_handle.height = 10;
    {
        var ctx = resize_handle.getContext("2d");
        ctx.beginPath();
        for (var i = 1; i <= 7; i += 3) {
            ctx.moveTo(8.5, i + 0.5);
            ctx.lineTo(i + 0.5, 8.5);
        }
        ctx.lineWidth = '1px';
        ctx.lineCap = 'round';
        ctx.lineJoin = 'round';
        ctx.strokeStyle = '#000000';
        ctx.stroke();
    }
    resizable_div = document.getElementById("resizable");
    resizable_div.appendChild(resize_handle);
    resize_handle.style.position = 'absolute';
    resize_handle.style.zIndex = 98;
    resize_handle.style.bottom = "0";
    resize_handle.style.right = "0";
    resize_handle.style.cursor = "se-resize";
    resize_handle.title = "Drag to resize the puzzle. Right-click to restore the default size.";
    var resize_xbase = null, resize_ybase = null, restore_pending = false;
    var resize_xoffset = null, resize_yoffset = null;
    var resize_puzzle = Module.cwrap('resize_puzzle',
                                     'void', ['number', 'number']);
    var restore_puzzle_size = Module.cwrap('restore_puzzle_size', 'void', []);
    resize_handle.oncontextmenu = function(event) { return false; }
    resize_handle.onmousedown = function(event) {
        if (event.button == 0) {
            var xy = element_coords(onscreen_canvas);
            resize_xbase = xy.x + onscreen_canvas.width / 2;
            resize_ybase = xy.y;
            resize_xoffset = xy.x + onscreen_canvas.width - event.pageX;
            resize_yoffset = xy.y + onscreen_canvas.height - event.pageY;
        } else {
            restore_pending = true;
        }
        resize_handle.setCapture(true);
        event.preventDefault();
    };
    window.addEventListener("mousemove", function(event) {
        if (resize_xbase !== null && resize_ybase !== null) {
            resize_puzzle((event.pageX + resize_xoffset - resize_xbase) * 2,
                          (event.pageY + resize_yoffset - resize_ybase));
            event.preventDefault();
            // Chrome insists on selecting text during a resize drag
            // no matter what I do
            if (window.getSelection)
                window.getSelection().removeAllRanges();
            else
                document.selection.empty();        }
    });
    window.addEventListener("mouseup", function(event) {
        if (resize_xbase !== null && resize_ybase !== null) {
            resize_xbase = null;
            resize_ybase = null;
            onscreen_canvas.focus(); // return focus to the puzzle
        } else if (restore_pending) {
            // If you have the puzzle at larger than normal size and
            // then right-click to restore, I haven't found any way to
            // stop Chrome and IE popping up a context menu on the
            // revealed piece of document when you release the button
            // except by putting the actual restore into a setTimeout.
            // Gah.
            setTimeout(function() {
                restore_pending = false;
                restore_puzzle_size();
                onscreen_canvas.focus();
            }, 20);
        }
        event.preventDefault();
    });

    // Run the C setup function, passing argv[1] as the fragment
    // identifier (so that permalinks of the form puzzle.html#game-id
    // can launch the specified id).
    Module.arguments = [location.hash];
    Module.run();

    // And if we get here with everything having gone smoothly, i.e.
    // we haven't crashed for one reason or another during setup, then
    // it's probably safe to hide the 'sorry, no puzzle here' div and
    // show the div containing the actual puzzle.
    document.getElementById("apology").style.display = "none";
    document.getElementById("puzzle").style.display = "inline";
}