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HTML 

              
                <div id="gameViewport">
    <canvas id="game" width="1" height="1"></canvas>
</div>
!

CSS 

              
                    #gameViewport {
        position: relative;
        background: #000;
        overflow: hidden;
        height: 0px;
        padding-top: 56.25%;
    }
    #game {
        width: 100%;
        height: 100%;
        position: absolute;
        top: 0px;
        left: 0px;
    }
!

JS 

              
                    (function() {

        const CANVAS = document.getElementById("game");
        const CIRCLE = Math.PI * 2;
        const FOCAL_LENGTH = 0.8;
        const KEYCODES = { 37: "left", 39: "right", 38: "forward", 40: "backward" };
        const MAP = [
            [1, 1, 1, 1, 1, 1, 1, 1, 1],
            [1, 0, 0, 0, 0, 0, 0, 0, 1],
            [1, 1, 1, 0, 1, 1, 1, 0, 1],
            [1, 0, 1, 0, 0, 0, 1, 0, 1],
            [1, 0, 1, 1, 0, 0, 1, 1, 1],
            [1, 0, 0, 0, 0, 0, 0, 0, 1],
            [1, 1, 1, 1, 1, 1, 1, 1, 1]
        ];
        const NO_WALL = { length2: Infinity };
        const RESOLUTION = 320;
        const START_QUADRANT = [1, 1];

        function Bitmap(src, width, height) {
            this.image = new Image();
            this.image.src = src;
            this.width = width;
            this.height = height;
        }

        function attachControls(game) {
            document.addEventListener("keydown", event => {
                const direction = KEYCODES[event.keyCode];
                if (!direction) {
                    return;
                }
                game.controls[direction] = true;
                event.preventDefault();
            }, false);
            document.addEventListener("keyup", event => {
                const direction = KEYCODES[event.keyCode];
                if (!direction) {
                    return;
                }
                game.controls[direction] = false;
                event.preventDefault();
            }, false);
        }

        function baseControls() {
            return {
                left: false,
                right: false,
                forward: false,
                backward: false
            };
        }

        function cast(game, angle, range) {
            const point = game.player;
            const sin = Math.sin(angle);
            const cos = Math.cos(angle);
            const inspect = (step, shiftX, shiftY, distance, offset) => {
                const dx = cos < 0 ? shiftX : 0;
                const dy = sin < 0 ? shiftY : 0;
                step.height = getMapPoint(game, step.x - dx, step.y - dy);
                step.distance = distance + Math.sqrt(step.length2);
                if (shiftX) {
                    step.shading = cos < 0 ? 2 : 0;
                } else {
                    step.shading = sin < 0 ? 2 : 1;
                }
                step.offset = offset - Math.floor(offset);
                return step;
            };
            const ray = origin => {
                const stepX = step(sin, cos, origin.x, origin.y);
                const stepY = step(cos, sin, origin.y, origin.x, true);
                const nextStep = stepX.length2 < stepY.length2
                    ? inspect(stepX, 1, 0, origin.distance, stepX.y)
                    : inspect(stepY, 0, 1, origin.distance, stepY.x);
                if (nextStep.distance > range) {
                    return [origin];
                }
                return [origin].concat(ray(nextStep));
            };
            const step = (rise, run, x, y, inverted) => {
                if (run === 0) {
                    return NO_WALL;
                }
                const dx = run > 0 ? Math.floor(x + 1) - x : Math.ceil(x - 1) - x;
                const dy = dx * (rise / run);
                return {
                    x: inverted ? y + dy : x + dx,
                    y: inverted ? x + dx : y + dy,
                    length2: dx * dx + dy * dy
                };
            };
            return ray({ x: point.x, y: point.y, height: 0, distance: 0 });
        }

        function createCamera(canvas, resolution, focalLength) {
            const width = canvas.width = window.innerWidth;
            const height = canvas.height = window.innerHeight;
            return {
                ctx: canvas.getContext("2d"),
                width,
                height,
                resolution,
                spacing: width / resolution,
                focalLength,
                range: 14,
                lightRange: 5,
                scale: width + height / 1200
            };
        }

        function createMap(grid) {
            return {
                grid,
                light: 0,
                wallTexture: new Bitmap("https://hotsource.dev/wp-content/uploads/2019/05/wastrel-wall.png", 512, 512),
                floorTexture: new Bitmap("https://hotsource.dev/wp-content/uploads/2019/05/wastrel-floor.jpg", 345, 345),
                skyTexture: new Bitmap("https://hotsource.dev/wp-content/uploads/2019/05/wastrel-skybox.jpg", 960, 640)
            }
        }

        function createPlayer() {
            return {
                x: START_QUADRANT[0] + 0.5,
                y: START_QUADRANT[1] + 0.5,
                direction: Math.PI * 0.3
            };
        }

        function drawColumns(game) {
            const { ctx } = game.camera;
            const { floorTexture, wallTexture } = game.map;
            ctx.save();
            const drawColumn = (column, ray, angle) => {
                // const texture = wallTexture;
                const left = Math.floor(column * game.camera.spacing);
                const width = Math.ceil(game.camera.spacing);
                let hit = -1;
                while (++hit < ray.length && ray[hit].height <= 0);
                for (let s = ray.length - 1; s >= 0; s--) {
                    const step = ray[s];
                    // var rainDrops = Math.pow(Math.random(), 3) * s;
                    // var rain = (rainDrops > 0) && project(0.1, angle, step.distance);
                    if (s === hit) {
                        const wallTextureX = Math.floor(wallTexture.width * step.offset);
                        const floorTextureX = Math.floor(floorTexture.width * step.offset);
                        const wall = project(step.height, angle, step.distance);
                        ctx.globalAlpha = 1;
                        // Walls:
                        ctx.drawImage(wallTexture.image, wallTextureX, 0, 1, wallTexture.height, left, wall.top, width, wall.height);
                        // Floor:
                        ctx.fillStyle = "#000";
                        ctx.fillRect(left, wall.top + wall.height, width, game.camera.height);
                        // ctx.drawImage(floorTexture.image,
                        //     floorTextureX, 0,
                        //     1, floorTexture.height,
                        //     left, wall.height * 2,
                        //     width, 1000);
                        ctx.fillStyle = "#000000";
                        ctx.globalAlpha = Math.max((step.distance + step.shading) / game.camera.lightRange - game.map.light, 0);
                        ctx.fillRect(left, wall.top, width, wall.height); // darkness
                    }
                    ctx.fillStyle = "#ffffff";
                    ctx.globalAlpha = 0.15;
                    // while (--rainDrops > 0) ctx.fillRect(left, Math.random() * rain.top, 1, rain.height);
                }
            };
            const project = (height, angle, distance) => {
                const z = distance * Math.cos(angle);
                const wallHeight = game.camera.height * height / z;
                const bottom = game.camera.height / 2 * (1 + 1 / z);
                return {
                    top: bottom - wallHeight,
                    height: wallHeight
                }; 
            };
            for (let column = 0; column < game.camera.resolution; column++) {
                const x = column / game.camera.resolution - 0.5;
                const angle = Math.atan2(x, game.camera.focalLength);
                const ray = cast(game, game.player.direction + angle, game.camera.range);
                drawColumn(column, ray, angle);
            }
            ctx.restore();
        }

        function drawSky(game) {
            const { light: ambient, skyTexture } = game.map;
            const { ctx } = game.camera;
            const { direction } = game.player;
            const width = skyTexture.width * (game.camera.height / skyTexture.height) * 2;
            const left = (direction / CIRCLE) * -width;
            ctx.save();
            ctx.drawImage(skyTexture.image, left, 0, width, game.camera.height);
            if (left < width - game.camera.width) {
                ctx.drawImage(skyTexture.image, left + width, 0, width, game.camera.height);
            }
            if (ambient > 0) {
                ctx.fillStyle = "#ffffff";
                ctx.globalAlpha = ambient * 0.1;
                ctx.fillRect(0, game.camera.height * 0.5, game.camera.width, game.camera.height * 0.5);
            }
            ctx.restore();
        }

        function getMapPoint(game, x, y) {
            const gameWidth = game.map.grid[0].length;
            const gameHeight = game.map.grid.length;
            const rx = Math.floor(x);
            const ry = Math.floor(y);
            if (rx < 0 || rx > gameWidth - 1 || ry < 0 || ry > gameHeight - 1) {
                return -1;
            }
            return game.map.grid[ry][rx];
        }

        function loop(callback) {
            let lastTime = 0;
            const handleFrame = time => {
                const seconds = (time - lastTime) / 1000;
                lastTime = time;
                if (seconds < 0.2) {
                    callback(seconds);
                }
                requestAnimationFrame(handleFrame);
            };
            requestAnimationFrame(handleFrame);
        }

        function newGame() {
            const game = {
                camera: createCamera(CANVAS, RESOLUTION, FOCAL_LENGTH),
                map: createMap(MAP),
                player: createPlayer(),
                controls: baseControls()
            };
            attachControls(game);
            return game;
        }

        function play(game) {
            loop(seconds => {
                updateMap(game, seconds);
                updatePlayer(game, seconds);
                render(game);
            });
        }

        function render(game) {
            drawSky(game);
            drawColumns(game);
        }

        function rotatePlayer(game, angle) {
            game.player.direction = (game.player.direction + angle + CIRCLE) % CIRCLE;
        }

        function updateMap(game, seconds) {
            if (game.map.light > 0) {
                game.map.light = Math.max(game.map.light - 10 * seconds, 0);
            } else if (Math.random() * 5 < seconds) {
                game.map.light = 2;
            }
        }

        function updatePlayer(game, seconds) {
            const { controls } = game;
            if (controls.left) {
                rotatePlayer(game, -Math.PI * seconds);
            }
            if (controls.right) {
                rotatePlayer(game, Math.PI * seconds);
            }
            if (controls.forward) {
                walkPlayer(game, 3 * seconds);
            }
            if (controls.backward) {
                walkPlayer(game, -3 * seconds);
            }
        }

        function walkPlayer(game, distance) {
            const dx = Math.cos(game.player.direction) * distance;
            const dy = Math.sin(game.player.direction) * distance;
            if (getMapPoint(game, game.player.x + dx, game.player.y) <= 0) {
                game.player.x += dx;
            }
            if (getMapPoint(game, game.player.x, game.player.y + dy) <= 0) {
                game.player.y += dy;
            }
        }

        // Start
        play(newGame());

    })();
!
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