Alright, so I've been working on a Checkers game in my free time using HTML 5 and JS. While I've not made a lot of progress just yet, I have hit somewhat of a brick wall. I'm not all that proficient in JS just yet, but I've done a fair amount of research concerning it, to little avail.
My problem is I can create and load images just fine, but when it comes to drawing them properly onto the canvas is when I get problems. When using drawImage(...); calls outside a loop, they will draw correctly, and more importantly, at the correct coordinates. Conversely, if I were to place a drawImage(...); call inside a loop, the images will display correctly, but at the coordinates of the last image to be drawn.
document.addEventListener('DOMContentLoaded',onLoad,false)
/* Holds information about a game piece on the board */
function onLoad() {
/* Grab the canvas element & context drawer */
var canv = document.getElementById("board");
var ctxt = canv.getContext("2d");
/*Initialize Board & Game Values*/
var rows = 8;
var cols = 8;
var evenTiles = "#CCC";
var oddTiles = "#444";
var board = [];
var red = new Image();
red.src = "Images/Red.png";
var black = new Image();
black.src = "Images/Black.png";
/* Initialize the underlying array "pieces" to default values */
for (a = 0; a < rows; a++) {
row = [];
for (b = 0; b < cols; b++) {
if (a < 2) {
if ((a % 2) == 0)
if ((b % 2) != 0)
row.push(new Piece(Piece.Color.RED, Piece.Status.NORMAL, b, a));
else
row.push(null);
else
if ((b % 2) == 0)
row.push(new Piece(Piece.Color.RED, Piece.Status.NORMAL, b, a));
else
row.push(null);
}
else if (a > (rows - 3)) {
if ((a % 2) == 0)
if ((b % 2) != 0)
row.push(new Piece(Piece.Color.BLACK, Piece.Status.NORMAL, b, a));
else
row.push(null);
else
if ((b % 2) == 0)
row.push(new Piece(Piece.Color.BLACK, Piece.Status.NORMAL, b, a));
else
row.push(null);
}
else
row.push(null);
}
board.push(row);
}
/* Draw the game board to the canvas */
for (a = 0; a < rows; a++) {
var row = (canv.height / rows) * a;
for (b = 0; b < cols; b++) {
var col = (canv.width / cols) * b;
if ((a % 2) == 0)
if ((b % 2) == 0)
ctxt.fillStyle = evenTiles;
else
ctxt.fillStyle = oddTiles;
else
if ((b % 2) == 0)
ctxt.fillStyle = oddTiles;
else
ctxt.fillStyle = evenTiles;
ctxt.fillRect(row, col, (canv.height / rows), (canv.width / cols));
//# PROBLEMATIC CODE #
if (board[a][b] != null) {
var piece = board[a][b];
if (piece.Color == Piece.Color.RED)
red.addEventListener("load", function () { ctxt.drawImage(red, piece.X * 100, piece.Y * 100) }, false);
else
black.addEventListener("load", function () { ctxt.drawImage(black, piece.X * 100, piece.Y * 100) }, false);
}
//# END PROBLEMATIC CODE #
}
}
}
The above code produces the following which draws all the pieces on top of one another at the last image's coordinates.
I'm thinking that the coordinates are changing, before the image is fully drawn, thus prompting the renderer to keep re-drawing it each time the variable changes. However, on the other hand, one would think that it has ample time to fully draw an image before it's called upon a second time.
Any suggestions?
I don't think it would be difficult at all to do it in HTML. You just need black and white DIV classes with fixed widths/heights and coordinate based ID's. The pieces can be CSS classes with centered background images. It would be very easy to move a piece by adding and removing the classes at particular coordinates.
I suppose its more based on what they'd like to do in the future. Learning to do it with canvas might be better if they're wanting to get more involved with making HTML5 based games.
As for the actual issue at hand, firstly create some sort of loading routine to load the images before the game is started. Then just reuse that image element to draw to the screen. I think the issue is arising from the very very very common mistake when writing callbacks. The load callback is saving a reference to the variable that holds the current peice (which means the piece that is referenced on image load is the next/last one in the loop). If you want to make your current version work wrap it in an IIFE http://benalman.com/news/2010/11/immediately-invoked-function-expression/ with the peice as a parameter.
Why not use HTML and CSS for the layout rather than a canvas? It would be far simpler.