ref: 3c3468355f8cf3dd644058ab239b948f8facebfa
dir: /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.
*/
// Because this script is run using <script defer>, we can guarantee
// that the DOM is complete, so it's OK to look up elements
// immediately. On the other hand, the Emscripten runtime hasn't
// started yet, so Module.cwrap isn't safe.
// 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
// requesting it for each 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 when main() returns nothing will get cleaned up so we remain
// able to call the puzzle's various callbacks.
//
// Page loading order:
//
// 1. The browser starts reading *.html (which comes from jspage.pl)
// 2. It finds the <script> tag. This is marked defer, so the
// browser will start fetching and parsing it, but not execute it
// until the page has loaded.
//
// Now the browser is loading *.html and *.js in parallel. The
// html is rendered as we go, and the js is deferred.
//
// 3. The HTML finishes loading. The browser is about to fire the
// `DOMContentLoaded` event (ie `onload`) but before that, it
// actually runs the deferred JS. This consists of
//
// (i) emccpre.js (this file). This sets up various JS variables
// including the emscripten Module object, which includes the
// environment variables and argv seen by main().
//
// (ii) emscripten's JS. This starts the WASM loading.
//
// When this JS execution is complete, the browser fires the `onload`
// event. This is ignored. It continues loading the WASM.
//
// 4. The WASM loading and initialisation completes. Emscripten's
// runtime calls the C `main` to actually start the puzzle. It
// then calls initPuzzle, which:
//
// (a) finds various DOM elements and bind them to variables,
// which depends on the HTML having loaded (it has).
//
// (b) makes various `cwrap` calls into the emscripten module to
// set up hooks; this depends on the emscripten JS having been
// loaded (it has).
var Module = {
'preRun': function() {
// Merge environment variables from HTML script element.
// This means you can add something like this to the HTML:
// <script id="environment" type="application/json">
// { "LOOPY_DEFAULT": "20x10t11dh" }
// </script>
var envscript = document.getElementById("environment");
var k, v;
if (envscript !== null)
for ([k, v] of
Object.entries(JSON.parse(envscript.textContent)))
ENV[k] = v;
},
// Pass argv[1] as the fragment identifier (so that permalinks of
// the form puzzle.html#game-id can launch the specified id).
'arguments': [decodeURIComponent(location.hash)],
'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;
var timer_reference;
// void timer_callback(double tplus);
//
// Called every frame while timing is active.
var timer_callback;
// The status bar object, if we have one.
var statusbar = document.getElementById("statusbar");
// 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_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_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 <ul> object implementing the game-type drop-down, and a list of
// the sub-lists inside it. Used by js_add_preset().
var gametypelist = document.getElementById("gametype");
var gametypesubmenus = [gametypelist];
// C entry point for miscellaneous events.
var command;
// The <form> encapsulating the menus. Used by
// js_get_selected_preset() and js_select_preset().
var menuform = document.getElementById("gamemenu");
// The two anchors used to give permalinks to the current puzzle. Used
// by js_update_permalinks().
var permalink_seed = document.getElementById("permalink-seed");
var permalink_desc = document.getElementById("permalink-desc");
// The various buttons. Undo and redo are used by js_enable_undo_redo().
var specific_button = document.getElementById("specific");
var random_button = document.getElementById("random");
var new_button = document.getElementById("new");
var restart_button = document.getElementById("restart");
var undo_button = document.getElementById("undo");
var redo_button = document.getElementById("redo");
var solve_button = document.getElementById("solve");
var save_button = document.getElementById("save");
var load_button = document.getElementById("load");
// A div element enclosing both the puzzle and its status bar, used
// for positioning the resize handle.
var resizable_div = document.getElementById("resizable");
// Alternatively, an extrinsically sized div that we will size the
// puzzle to fit.
var containing_div = document.getElementById("puzzlecanvascontain");
// 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};
}
// Higher-level mouse helper function to specifically map mouse
// coordinates into the coordinates on a canvas that appear under it.
// This depends on the details of how a canvas gets scaled by CSS.
function canvas_mouse_coords(event, element) {
var rcoords = relative_mouse_coords(event, element);
// Assume that the CSS object-fit property is "fill" (the default).
var xscale = element.width / element.offsetWidth;
var yscale = element.height / element.offsetHeight;
return {x: rcoords.x * xscale, y: rcoords.y * yscale}
}
// Set the font on a CanvasRenderingContext2d based on the CSS font
// for the canvas, the requested size, and whether we want something
// monospaced.
function canvas_set_font(ctx, size, monospaced) {
var s = window.getComputedStyle(onscreen_canvas);
// First set something that we're certain will work. Constructing
// the font string from the computed style is a bit fragile, so
// this acts as a fallback.
ctx.font = `${size}px ` + (monospaced ? "monospace" : "sans-serif");
// In CSS Fonts Module Level 4, "font-stretch" gets serialised as
// a percentage, which can't be used in
// CanvasRenderingContext2d.font, so we omit it.
ctx.font = `${s.fontStyle} ${s.fontWeight} ${size}px ` +
(monospaced ? "monospace" : s.fontFamily);
}
// Enable and disable items in the CSS menus.
function disable_menu_item(item, disabledFlag) {
item.disabled = disabledFlag;
}
// Dialog-box functions called from both C and JS.
function dialog_init(titletext) {
// Forward compatibility: Delete form and dimmer if they already
// exist.
dlg_dimmer = document.getElementById("dlgdimmer");
if (dlg_dimmer) dlg_dimmer.parentElement.removeChild(dlg_dimmer);
dlg_form = document.getElementById("dlgform");
if (dlg_form) dlg_form.parentElement.removeChild(dlg_form);
// Create an overlay on the page which darkens everything
// beneath it.
dlg_dimmer = document.createElement("div");
dlg_dimmer.id = "dlgdimmer";
// Now create a form which sits on top of that in turn.
dlg_form = document.createElement("form");
dlg_form.id = "dlgform";
var title = document.createElement("h2");
title.appendChild(document.createTextNode(titletext));
dlg_form.appendChild(title);
dlg_return_funcs = [];
}
function dialog_launch(ok_function, cancel_function) {
// Put in the OK and Cancel buttons at the bottom.
var button;
if (ok_function) {
button = document.createElement("input");
button.type = "button";
button.value = "OK";
button.onclick = ok_function;
dlg_form.appendChild(button);
}
if (cancel_function) {
button = document.createElement("input");
button.type = "button";
button.value = "Cancel";
button.onclick = cancel_function;
dlg_form.appendChild(button);
}
document.body.appendChild(dlg_dimmer);
document.body.appendChild(dlg_form);
dlg_form.querySelector("input,select,a").focus();
}
function dialog_cleanup() {
document.body.removeChild(dlg_dimmer);
document.body.removeChild(dlg_form);
dlg_dimmer = dlg_form = null;
onscreen_canvas.focus();
}
// Init function called early in main().
function initPuzzle() {
// Construct the off-screen canvas used for double buffering.
onscreen_canvas = document.getElementById("puzzlecanvas");
offscreen_canvas = document.createElement("canvas");
ctx = offscreen_canvas.getContext('2d', { alpha: false });
// 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).
var mousedown = Module.cwrap('mousedown', 'boolean',
['number', 'number', 'number']);
var button_phys2log = [null, null, null];
var buttons_down = function() {
var i, toret = 0;
for (i = 0; i < 3; i++)
if (button_phys2log[i] !== null)
toret |= 1 << button_phys2log[i];
return toret;
};
onscreen_canvas.onmousedown = function(event) {
if (event.button >= 3)
return;
var xy = canvas_mouse_coords(event, onscreen_canvas);
var logbutton = event.button;
if (event.shiftKey)
logbutton = 1; // Shift-click overrides to middle button
else if (event.ctrlKey)
logbutton = 2; // Ctrl-click overrides to right button
if (mousedown(xy.x, xy.y, logbutton))
event.preventDefault();
button_phys2log[event.button] = logbutton;
onscreen_canvas.setCapture(true);
};
var mousemove = Module.cwrap('mousemove', 'boolean',
['number', 'number', 'number']);
onscreen_canvas.onmousemove = function(event) {
var down = buttons_down();
if (down) {
var xy = canvas_mouse_coords(event, onscreen_canvas);
if (mousemove(xy.x, xy.y, down))
event.preventDefault();
}
};
var mouseup = Module.cwrap('mouseup', 'boolean',
['number', 'number', 'number']);
onscreen_canvas.onmouseup = function(event) {
if (event.button >= 3)
return;
if (button_phys2log[event.button] !== null) {
var xy = canvas_mouse_coords(event, onscreen_canvas);
if (mouseup(xy.x, xy.y, button_phys2log[event.button]))
event.preventDefault();
button_phys2log[event.button] = null;
}
};
// Set up keyboard handlers. We call event.preventDefault()
// in the keydown handler if it looks like we might have
// done something with the key. This means that users
// of this puzzle collection in other media
// can indulge their instinct to press ^R for redo, for example,
// without accidentally reloading the page.
var key = Module.cwrap('key', 'boolean', ['number', 'string', 'string',
'number', 'number', 'number']);
onscreen_canvas.onkeydown = function(event) {
if (key(event.keyCode, event.key, event.char, event.location,
event.shiftKey ? 1 : 0, event.ctrlKey ? 1 : 0))
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().
if (specific_button) specific_button.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);
};
if (random_button) random_button.onclick = function(event) {
if (dlg_dimmer === null)
command(1);
};
if (new_button) new_button.onclick = function(event) {
if (dlg_dimmer === null)
command(5);
};
if (restart_button) restart_button.onclick = function(event) {
if (dlg_dimmer === null)
command(6);
};
if (undo_button) undo_button.onclick = function(event) {
if (dlg_dimmer === null)
command(7);
};
if (redo_button) redo_button.onclick = function(event) {
if (dlg_dimmer === null)
command(8);
};
if (solve_button) solve_button.onclick = function(event) {
if (dlg_dimmer === null)
command(9);
};
// 'number' is used for C pointers
var get_save_file = Module.cwrap('get_save_file', 'number', []);
var free_save_file = Module.cwrap('free_save_file', 'void', ['number']);
var load_game = Module.cwrap('load_game', 'void', ['string', 'number']);
if (save_button) save_button.onclick = function(event) {
if (dlg_dimmer === null) {
var savefile_ptr = get_save_file();
var savefile_text = UTF8ToString(savefile_ptr);
free_save_file(savefile_ptr);
dialog_init("Download saved-game file");
dlg_form.appendChild(document.createTextNode(
"Click to download the "));
var a = document.createElement("a");
a.download = "puzzle.sav";
a.href = "data:application/octet-stream," +
encodeURIComponent(savefile_text);
a.appendChild(document.createTextNode("saved-game file"));
dlg_form.appendChild(a);
dlg_form.appendChild(document.createTextNode("."));
dlg_form.appendChild(document.createElement("br"));
dialog_launch(function(event) {
dialog_cleanup();
});
}
};
if (load_button) load_button.onclick = function(event) {
if (dlg_dimmer === null) {
var input = document.createElement("input");
input.type = "file";
input.multiple = false;
input.addEventListener("change", function(event) {
if (input.files.length == 1) {
var file = input.files.item(0);
var reader = new FileReader();
reader.addEventListener("loadend", function() {
var string = reader.result;
load_game(string, string.length);
});
reader.readAsText(file);
}
});
input.click();
onscreen_canvas.focus();
}
};
// Find the next or previous item in a menu, or null if there
// isn't one. Skip list items that don't have a child (i.e.
// separators) or whose child is disabled.
function isuseful(item) {
return item.querySelector(":scope > :not(:disabled)");
}
function nextmenuitem(item) {
do item = item.nextElementSibling;
while (item !== null && !isuseful(item));
return item;
}
function prevmenuitem(item) {
do item = item.previousElementSibling;
while (item !== null && !isuseful(item));
return item;
}
function firstmenuitem(menu) {
var item = menu && menu.firstElementChild;
while (item !== null && !isuseful(item))
item = item.nextElementSibling;
return item;
}
function lastmenuitem(menu) {
var item = menu && menu.lastElementChild;
while (item !== null && !isuseful(item))
item = item.previousElementSibling;
return item;
}
// Keyboard handlers for the menus.
function menukey(event) {
var target = event.target;
var key = event.key;
var thisitem = target.closest("li");
var thismenu = thisitem.closest("ul");
var targetitem = null;
var parentitem;
var parentitem_up = null;
var parentitem_sideways = null;
var submenu;
function ishorizontal(menu) {
// Which direction does this menu go in?
var cs = window.getComputedStyle(menu);
return cs.display == "flex" && cs.flexDirection == "row";
}
if (dlg_dimmer !== null)
return;
if (["1", "2", "3", "4", "5", "6", "7", "8", "9", "0"]
.includes(key)) {
var shortcutitem = thismenu.querySelectorAll(
":scope > li:not([role='separator']")[(Number(key) + 9) % 10];
if (shortcutitem) {
target = shortcutitem.firstElementChild;
target.focus();
thisitem = target.closest("li");
key = "Enter";
}
}
if (!["ArrowLeft", "ArrowRight", "ArrowUp", "ArrowDown", "Enter",
"Escape", "Backspace", "SoftRight", "F10"]
.includes(key))
return;
if (ishorizontal(thismenu)) {
// Top-level menu bar.
if (key == "ArrowLeft")
targetitem = prevmenuitem(thisitem) || lastmenuitem(thismenu);
else if (key == "ArrowRight")
targetitem = nextmenuitem(thisitem) || firstmenuitem(thismenu);
else if (key == "ArrowUp")
targetitem = lastmenuitem(thisitem.querySelector("ul"));
else if (key == "ArrowDown" || key == "Enter")
targetitem = firstmenuitem(thisitem.querySelector("ul"));
} else {
// Ordinary vertical menu.
parentitem = thismenu.closest("li");
if (parentitem) {
if (ishorizontal(parentitem.closest("ul")))
parentitem_up = parentitem;
else
parentitem_sideways = parentitem;
}
if (key == "ArrowUp")
targetitem = prevmenuitem(thisitem) || parentitem_up ||
lastmenuitem(thismenu);
else if (key == "ArrowDown")
targetitem = nextmenuitem(thisitem) || parentitem_up ||
firstmenuitem(thismenu);
else if (key == "ArrowRight")
targetitem = thisitem.querySelector("li") ||
(parentitem_up && nextmenuitem(parentitem_up));
else if (key == "Enter")
targetitem = thisitem.querySelector("li");
else if (key == "ArrowLeft")
targetitem = parentitem_sideways ||
(parentitem_up && prevmenuitem(parentitem_up));
else if (key == "Backspace")
targetitem = parentitem;
}
if (targetitem)
targetitem.firstElementChild.focus();
else if (key == "Enter")
target.click();
else if (key == "Escape" || key == "SoftRight" ||
key == "F10" || key == "Backspace")
// Leave the menu entirely.
onscreen_canvas.focus();
// Prevent default even if we didn't do anything, as long as this
// was an interesting key.
event.preventDefault();
event.stopPropagation();
}
menuform.addEventListener("keydown", menukey);
// Open documentation links within the application in KaiOS.
for (var elem of document.querySelectorAll("#gamemenu a[href]")) {
elem.addEventListener("click", function(event) {
window.open(event.target.href);
event.preventDefault();
});
}
// 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);
event.preventDefault();
event.stopPropagation();
}
if (dlg_dimmer !== null && event.keyCode == 27) {
command(4);
event.preventDefault();
event.stopPropagation();
}
}, true);
// Arrange that the softkey labels are clickable. This logically
// belongs as a click handler, but by the time the click event
// fires, the input focus is in the wrong place.
function button_to_key(key) {
return function(mevent) {
mevent.stopPropagation();
mevent.preventDefault();
var kevent = new KeyboardEvent("keydown", {
key: key, view: window, bubbles: true});
document.activeElement.dispatchEvent(kevent);
};
}
for (var elem of document.querySelectorAll(".lsk"))
elem.addEventListener("mousedown", button_to_key("SoftLeft"));
for (var elem of document.querySelectorAll(".csk"))
elem.addEventListener("mousedown", button_to_key("Enter"));
for (var elem of document.querySelectorAll(".rsk"))
elem.addEventListener("mousedown", button_to_key("SoftRight"));
document.addEventListener("keydown", function(event) {
// Key to open the menu on KaiOS.
if ((event.key == "SoftRight" || event.key == "F10") &&
!menuform.contains(document.activeElement)) {
menuform.querySelector("li div, li button").focus();
event.preventDefault();
event.stopPropagation();
}
});
// Event handler to fake :focus-within on browsers too old for
// it (like KaiOS 2.5). Browsers without :focus-within are also
// too old for focusin/out events, so we have to use focus events
// which don't bubble but can be captured.
//
// A button losing focus because it was disabled doesn't generate
// a blur event, so we do this entirely in the focus handler.
document.documentElement.addEventListener("focus", function(event) {
for (var elem = event.target; elem; elem = elem.parentElement)
elem.classList.add("focus-within");
for (elem of
Array.from(document.getElementsByClassName("focus-within")))
if (!elem.contains(event.target))
elem.classList.remove("focus-within");
}, true);
// 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']);
if (resizable_div !== null) {
var resize_handle = document.getElementById("resizehandle");
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.offsetWidth / 2;
resize_ybase = xy.y;
resize_xoffset =
xy.x + onscreen_canvas.offsetWidth - event.pageX;
resize_yoffset =
xy.y + onscreen_canvas.offsetHeight - event.pageY;
} else {
restore_pending = true;
}
resize_handle.setCapture(true);
event.preventDefault();
};
window.addEventListener("mousemove", function(event) {
if (resize_xbase !== null && resize_ybase !== null) {
var dpr = window.devicePixelRatio || 1;
resize_puzzle(
(event.pageX + resize_xoffset - resize_xbase) * dpr * 2,
(event.pageY + resize_yoffset - resize_ybase) * dpr);
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
event.preventDefault();
} 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();
}
});
}
var rescale_puzzle = Module.cwrap('rescale_puzzle', 'void', []);
/*
* If the puzzle is sized to fit the page, try to detect changes
* of size of the containing element. Ideally this would use a
* ResizeObserver on the containing_div, but I want this to work
* on KaiOS 2.5, which doesn't have ResizeObserver. Instead we
* watch events that might indicate that the div has changed size.
*/
if (containing_div !== null) {
var resize_handler = function(event) {
rescale_puzzle();
}
window.addEventListener("resize", resize_handler);
// Also catch the point when the document finishes loading,
// since sometimes we seem to get the div's size too early.
window.addEventListener("load", resize_handler);
}
}
function post_init() {
/*
* Arrange to detect changes of device pixel ratio. Adapted from
* <https://developer.mozilla.org/en-US/docs/Web/API/Window/
* devicePixelRatio> (CC0) to work on older browsers.
*/
var rescale_puzzle = Module.cwrap('rescale_puzzle', 'void', []);
var mql = null;
var update_pixel_ratio = function() {
var dpr = window.devicePixelRatio;
if (mql !== null)
mql.removeListener(update_pixel_ratio);
mql = window.matchMedia(`(resolution: ${dpr}dppx)`);
mql.addListener(update_pixel_ratio);
rescale_puzzle();
}
update_pixel_ratio();
// 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.
var apology = document.getElementById("apology");
if (apology !== null) apology.style.display = "none";
document.getElementById("puzzle").style.display = "";
// Default to giving keyboard focus to the puzzle.
onscreen_canvas.focus();
}