Scrolling tiles

var playerX, playerX = whatever;

startX = floor((playerX - HALF_SCREEN_WIDTH) / TILE_WIDTH);
xOffset = playerX % TILE_WIDTH;

startY = floor((playerY - HALF_SCREEN_HEIGHT) / TILE_HEIGHT);
yOffset = playerY % TILE_HEIGHT;

for (x from 0 to TILES_ACROSS_SCREEN)
{
	for (y from 0 to TILES_DOWN_SCREEN)
	{
		drawTile(tileX = startX+x,
			tileY = startY + y,
			xPos = (x * TILE_WIDTH) - xOffset,
			yPos = (y * TILE_HEIGHT) - yOffset);
	}
}