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<canvas id="canvas" width="500" height="500"> </canvas>
<!-- This is a repeating tiling example that I isolated from my game Edge Not Found, which you can play here: https://auroriax.itch.io/edge-not-found and the full source code can be found at https://github.com/Auroriax/js13k-2020 -->
<!-- This code snippet is released under MIT: https://opensource.org/licenses/MIT -->
html, body, canvas {
width: 100%;
height: 100%;
margin: 0;
overflow: hidden;
}
//Grabbing references
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d", { alpha: false });
//Setting canvas to be as wide as the screen
canvas.width = canvas.clientWidth;
canvas.height = canvas.clientHeight;
//These values control how "offset" the level is. One or both of these must be 0.
//Keep the values low for the best effect (never higher than level width/height).
//If you don't get how it works, consider playing Edge Not Found for a bit. :)
const levelOffsetX = 0;
const levelOffsetY = 0;
//In number of tiles. Since we don't have the level state data like we would in the game
const gridWidth = 4;
const gridHeight = 8;
//Loading an image to use as an example level
var img = new Image();
img.onload = function () {
DrawRepeat(img);
};
img.src = "https://assets.codepen.io/5343800/enf_examplelevel_320.png";
function DrawRepeat(img) {
if (img == null) {
return;
}
//Cleaning canvas
ctx.fillStyle = "white";
ctx.fillRect(0, 0, canvas.width, canvas.height);
//Pixel size of the level is important for our calculations later, so we save it here
var levelWidth = img.width;
var levelHeight = img.height;
//Decide where to draw the level to make it appear in the middle of the screen
var cameraX = Math.round(canvas.width * 0.5 - levelWidth * 0.5);
var cameraY = Math.round(canvas.height * 0.5 - levelHeight * 0.5);
var clipOffset = 20; //Adds extra padding to make sure the screen border is filled. In pixels.
//Determine how often we can redraw the level before hitting the screen border
var screenWidthRatio = Math.ceil(
((canvas.width - levelWidth + clipOffset) / levelWidth) * 0.5
);
var screenHeightRatio = Math.ceil(
((canvas.height - levelHeight + clipOffset) / levelHeight) * 0.5
);
//Add a little safety padding in case the level wrapping is offset
if (levelOffsetX != 0) {
screenWidthRatio += 2;
}
if (levelOffsetY != 0) {
screenHeightRatio += 2;
}
ctx.fillStyle = "red";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.font = "40px sans-serif";
//Fill the screen with levels, following the offset
for (let y = -Math.abs(screenHeightRatio); y <= Math.abs(screenHeightRatio); y++) {
for (let x = -Math.abs(screenWidthRatio); x <= Math.abs(screenWidthRatio); x++) {
//Set alpha so levels further away from the screen center are more translucent
ctx.globalAlpha = Math.max(0, 1 - Math.abs(y) * 0.1 - Math.abs(x * 0.1));
if (ctx.globalAlpha > 0) { //Only draw if it will actually be visible!
var levelX = cameraX + levelWidth * x + levelOffsetX * (levelWidth / gridWidth) * y;
var levelY = cameraY + levelHeight * y + levelOffsetY * (levelHeight / gridHeight) * x
ctx.drawImage(img, levelX, levelY);
//Unsure how the location is decided? Uncomment the next line to display coordinates!
//ctx.fillText(x+","+y,levelX + levelWidth * 0.5, levelY + levelHeight * 0.5);
}
}
}
}
//Also redraw images when resizing window
window.onresize = function() {
canvas.width = canvas.clientWidth;
canvas.height = canvas.clientHeight;
DrawRepeat(img);
};
Also see: Tab Triggers