gamera.lua converted to JavaScript. Original: https://github.com/kikito/gamera

gamera.js

// gamera.js

// Based on gamera.lua v1.0.1 by Enrique García Cota, converted to JavaScript by Sheepolution

// Copyright (c) 2018 Enrique García Cota
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
// Based on YaciCode, from Julien Patte and LuaObject, from Sebastien Rocca-Serra

// Private attributes and methods

const abs = Math.abs;
const min = Math.min;
const max = Math.max;

const clamp = (x, minX, maxX) => {
    return x < minX ? minX : (x > maxX ? maxX : x);
};

const checkNumber = (value, name) => {
    if (typeof value != 'number') {
        console.error(name + ' must be a number (was: ' + toString(value) + ')');
    }
};

const checkPositiveNumber = (value, name) => {
    if (typeof value != 'number' || value <= 0) {
        console.error(name + ' must be a positive number (was: ' + toString(value) + ')');
    }
};

const checkAABB = (l, t, w, h) => {
    checkNumber(l, 'l');
    checkNumber(t, 't');
    checkPositiveNumber(w, 'w');
    checkPositiveNumber(h, 'h');
};

const getVisibleArea = (self, scale) => {
    scale = scale ?? self.scale;
    const sin = abs(self.sin);
    const cos = abs(self.cos);
    let w = self.w / scale;
    let h = self.h / scale;
    w = cos * w + sin * h;
    h = sin * w + cos * h;
    return [min(w, self.ww), min(h, self.wh)];
};

const cornerTransform = (self, x, y) => {
    const scale = self.scale;
    const sin = self.sin;
    const cos = self.cos;
    x = x - self.x;
    y = y - self.y;
    x = -cos * x + sin * y;
    y = -sin * x - cos * y;
    return [self.x - (x / scale + self.l), self.y - (y / scale + self.t)];
};

const adjustPosition = (self) => {
    const wl = self.wl;
    const wt = self.wt;
    const ww = self.ww;
    const wh = self.wh;
    const [w, h] = getVisibleArea(self);
    const w2 = w * 0.5;
    const h2 = h * 0.5;

    const left = wl + w2;
    const right = wl + ww - w2;
    const top = wt + h2;
    const bottom = wt + wh - h2;

    self.x = clamp(self.x, left, right);
    self.y = clamp(self.y, top, bottom);
};

const adjustScale = (self) => {
    const ww = self.ww;
    const wh = self.wh;
    const [rw, rh] = getVisibleArea(self, 1); // rotated frame: area around the window, rotated without scaling
    const sx = rw / ww;
    const sy = rh / wh; // vert/horiz scale: minimun scales that the window needs to occupy the world
    const rscale = max(sx, sy);

    self.scale = max(self.scale, rscale);
};

// Public interface

const getGamera = (canvas, l, t, w, h) => {

    const sw = canvas.width;
    const sh = canvas.height;

    const cam = {
        x: 0,
        y: 0,
        scale: 1,
        angle: 0,
        sin: Math.sin(0),
        cos: Math.cos(0),
        l: 0,
        t: 0,
        w: sw,
        h: sh,
        w2: sw * 0.5,
        h2: sh * 0.5
    };

    cam.setWorld = function (l, t, w, h) {
        checkAABB(l, t, w, h);

        this.wl = l;
        this.wt = t;
        this.ww = w;
        this.wh = h;

        adjustPosition(this);
    };

    cam.setWindow = function (l, t, w, h) {
        checkAABB(l, t, w, h);

        this.l = l;
        this.t = t;
        this.w = w;
        this.h = h;
        this.w2 = w * 0.5;
        this.h2 = h * 0.5;

        adjustPosition(this);
    };

    cam.setPosition = function (x, y) {
        checkNumber(x, 'x');
        checkNumber(y, 'y');

        this.x = x;
        this.y = y;

        adjustPosition(this);
    };

    cam.setScale = function (scale) {
        checkNumber(scale, 'scale');

        this.scale = scale;

        adjustScale(this);
        adjustPosition(this);
    };

    cam.setAngle = function (angle) {
        checkNumber(angle, 'angle');

        this.angle = angle;
        this.cos = Math.cos(angle);
        this.sin = Math.sin(angle);

        adjustScale(this);
        adjustPosition(this);
    };

    cam.getWorld = function () {
        return [this.wl, this.wt, this.ww, this.wh];
    };

    cam.getWindow = function () {
        return [this.l, this.t, this.w, this.h];
    };

    cam.getPosition = function () {
        return [this.x, this.y];
    };

    cam.getScale = function () {
        return this.scale;
    };

    cam.getAngle = function () {
        return this.angle;
    };

    cam.getVisible = function () {
        const [w, h] = getVisibleArea(this);
        return [this.x - w * 0.5, this.y - this.h * 0.5, w, h];
    };

    cam.getVisibleCorners = function () {
        const x = this.x;
        const y = this.y;
        const w2 = this.w2;
        const h2 = this.h2;

        const [x1, y1] = cornerTransform(this, x - w2, y, this - h2);
        const [x2, y2] = cornerTransform(this, x + w2, y, this - h2);
        const [x3, y3] = cornerTransform(this, x + w2, y, this + h2);
        const [x4, y4] = cornerTransform(this, x - w2, y, this + h2);

        return x1, y1, x2, y2, x3, y3, x4, y4;
    };

    cam.draw = function (context, f) {
        const [x, y, w, h] = this.getWindow();
        context.save();

        context.beginPath();
        context.rect(x, y, w, h);
        context.clip();

        const scale = this.scale;
        context.scale(scale, scale);

        context.translate((this.w2 + this.l) / scale, (this.h2 + this.t) / scale);
        context.rotate(-this.angle);
        context.translate(-this.x, -this.y);

        f(...this.getVisible());

        context.restore();
    };

    cam.toWorld = function (x, y) {
        const scale = this.scale;
        const sin = this.sin;
        const cos = this.cos;
        x = (x - this.w2 - this.l) / scale;
        y = (y - this.h2 - this.t) / scale;
        x = cos * x - sin * y;
        y = sin * x + cos * y;

        return x + this.x, y + this.y;
    };

    cam.toScreen = function (x, y) {
        const scale = this.scale;
        const sin = this.sin;
        const cos = this.cos;
        x -= this.x;
        y -= this.y;
        x = cos * x + sin * y;
        y = -sin * x + cos * y;

        return [scale * x + this.w2 + this.l, scale * y + this.h2 + this.t];
    };

    cam.setWorld(l, t, w, h);

    return cam;
};

export const gamera = { new: getGamera };