<canvas> Go/Baduk/Weiqi Game Board

Question

I'm experimenting a bit with the new tag and I've already hit my first roadbump. I figured I'd start getting my feet wet by implementing a version of the classic board game Go/Baduk/Weiqi.

I've drawn the xy grid using moveTo() and lineTo(), and I've drawn a wood background using fillRect() that needs to be "under" that XY grid of course.

However, therein lies my problem. The fillRect() background is drawn on top of the grid - thus obscuring the grid.

How do I reverse this? Here's what I'm working with:

        var boardSize = 19;                 
        var gridSpacing = 25;
        var gridSize = boardSize * gridSpacing;

        var xStart = (window.innerWidth / 2) - (gridSize / 2) + 0.5;
        var yStart = (window.innerHeight / 2) - (gridSize / 2) + 0.5;
        var xEnd = xStart + gridSize;
        var yEnd = yStart + gridSize;


        var gridContext = canvas.getContext("2d");

        gridContext.beginPath();

        // Draw the board x lines
        for (var x = xStart; x <= xEnd; x += gridSpacing)
        {
            gridContext.moveTo(x, yStart);
            gridContext.lineTo(x, yEnd);
        }

        // Draw the board y lines
        for (var y = yStart; y <= yEnd; y += gridSpacing)
        {
            gridContext.moveTo(xStart, y);
            gridContext.lineTo(xEnd, y);
        }

        gridContext.strokeStyle = "#000000";
        gridContext.stroke();

        // Create new image object to use as pattern
        var img = new Image();
        img.src = 'bg_wood.jpg';
        img.onload = function()
        {
            var boardBG = gridContext.createPattern(img, 'repeat');
            gridContext.fillStyle = boardBG;
            gridContext.fillRect(xStart, yStart, gridSize, gridSize);
        }

Answer 1

Try using gridContext.globalCompositeOperation = 'destination-over'; when drawing the background.