112 lines
3 KiB
JavaScript
112 lines
3 KiB
JavaScript
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/**
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* @author tint
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* @template Data, Input
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*/
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export class Game {
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/**
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* @param {number} history How many frames of history to keep in memory
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* @param {(data: Data, input: Input, frame: number) => Data} advance The function to apply game logic. For rollback to work properly, this must be a pure function, and can't mutate inputs.
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*/
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constructor(history, advance) {
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this.historysize = history;
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this.advance = advance;
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/** @type {{data: Data, input: Input}[]} */
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this.history = [];
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this.historyStart = 0;
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// the game may have inputs from the "future"
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// (local input delay to make sure inputs play at the same time on all machines)
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// so the "present" isn't always the latest frame
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// the game loop should set this every frame
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this.currentFrame = 0;
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}
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startHistory(frame, data) {
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this.historyStart = frame;
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this.history = [{ data }];
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this.currentFrame = frame;
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}
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getHistory(frame) {
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return this.history[frame - this.historyStart];
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}
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getFrame() {
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return this.historyStart + this.history.length - 1;
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}
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getCurrentData() {
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const entry = this.history[this.history.length - 1];
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return entry && entry.data;
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}
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/**
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* Sets the input at a specific frame. If that frame is in history,
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* the game will be rewound, the input applied, and then fast-forwarded to the current head.
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* If the frame is ahead of the current latest frame, the game will be run until that frame.
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* @param {number} frame The time to apply the input at
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* @param {Input} input The input
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*/
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setInput(frame, input) {
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this.editFrame(frame, index => {
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let past = this.history[index - 1];
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if(index === 0) {
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past = { data: undefined };
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}
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this.history[index] = {
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input,
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data: this.advance(past ? past.data : undefined, input, frame),
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};
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});
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}
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setData(frame, data) {
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this.editFrame(frame, index => {
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this.history[index] = {
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data,
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input: this.history[index] && this.history[index].input,
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}
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});
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}
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/**
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* @param {number} frame
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* @param {(index: number) => void} edit
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*/
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editFrame(frame, edit) {
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const head = this.historyStart + this.history.length;
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if(frame < head) {
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if(frame < this.historyStart) {
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throw new Error("Tried to edit a past frame not in history:", frame);
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}
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edit(frame - this.historyStart);
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// fast forward back to the present with the new data
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for(let i = frame + 1; i < head; i++) {
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const past = this.history[i - this.historyStart - 1];
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this.history[i - this.historyStart].data = this.advance(
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past ? past.data : undefined,
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this.history[i - this.historyStart].input,
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i
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);
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}
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} else {
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// fast forward the inbetween frames with no input
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for(let i = head; i < frame; i++) {
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const entry = this.history[i - this.historyStart - 1];
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this.history[i - this.historyStart] = {
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input: undefined,
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data: this.advance(entry ? entry.data : undefined, undefined, i),
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};
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}
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edit(frame - this.historyStart);
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}
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while(this.history.length > this.historysize) {
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this.history.shift();
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this.historyStart++;
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}
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}
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}
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