libpgs/src/pgsRendererImpl.ts

Renderer for graphical subtitles (PGS) in the browser.

import {PgsRendererHelper} from "./pgsRendererHelper";

/**
 * The base for handling pgs loading and rendering. There are different ways to render a subtitle file. Modern browser
 * support a more efficient asynchrone method using a web-worker. But if this isn't working for the current browser
 * a more compatible implementation can be used.
 */
export abstract class PgsRendererImpl {

    private updateTimestamps: number[] = [];
    private previousTimestampIndex: number = 0;

    /**
     * Is called when the timestamps were updated.
     */
    public onTimestampsUpdated?: () => void;

    /**
     * Sets the update timestamps and invokes an update event.
     * @param updateTimestamps The new array of update timestamps.
     */
    protected setUpdateTimestamps(updateTimestamps: number[]): void {
        // Stores the update timestamps, so we don't need to push the timestamp to the worker on every tick.
        // Instead, we push the timestamp index if it was changed.
        this.updateTimestamps = updateTimestamps;

        // Notify timestamp updates.
        if (this.onTimestampsUpdated) {
            this.onTimestampsUpdated();
        }
    }

    /**
     * Renders the subtitle for the given timestamp.
     * @param time The timestamp in seconds.
     */
    public renderAtTimestamp(time: number): void {
        const index = PgsRendererHelper.getIndexFromTimestamps(time, this.updateTimestamps);
        this.renderAtIndex(index);
    }

    /**
     * Renders the subtitle at the given timestamp index.
     * @param index The timestamp index.
     */
    public renderAtIndex(index: number): void {
        // Only render if the subtitle index was changed!
        if (this.previousTimestampIndex === index) return;
        this.previousTimestampIndex = index;

        this.render(index);
    }

    /**
     * Renders the subtitle at the given timestamp index. Internal render method to overwrite.
     * @param index The timestamp index.
     */
    protected abstract render(index: number): void;

    /**
     * Loads the subtitle file from the given url.
     * @param url The url to the PGS file.
     */
    public abstract loadFromUrl(url: string): void;

    /**
     * Loads the subtitle file from the given buffer.
     * @param buffer The PGS data.
     */
    public abstract loadFromBuffer(buffer: ArrayBuffer): void;

    /**
     * Disposes the renderer.
     */
    public abstract dispose(): void;
}