@woosh/meep-engine/src/engine/asset/loaders/image/jpeg/buildComponentData.js

Pure JavaScript game engine. Fully featured and production ready.

import { idct8x8_float } from "./idct8x8_float.js";

/**
 *
 * @param {JpegFrameComponent} component
 * @return {Uint8Array[]} lines
 */
export function buildComponentData(component) {
    /**
     *
     * @type {Uint8Array[]}
     */
    const lines = [];

    const blocks_per_line = component.blocksPerLine;
    const blocks_per_column = component.blocksPerColumn;
    const samples_per_line = blocks_per_line << 3;

    // Only 1 used per invocation of this function and garbage collected after invocation, so no need to account for its memory footprint.
    const r = new Uint8Array(64);

    let i, j;
    for (let block_row = 0; block_row < blocks_per_column; block_row++) {
        const scan_line = block_row << 3;

        // align memory
        const lines_buffer = new ArrayBuffer(samples_per_line * 8);

        for (i = 0; i < 8; i++) {
            const line = new Uint8Array(lines_buffer, i * samples_per_line, samples_per_line);

            lines.push(line);
        }

        for (let block_col = 0; block_col < blocks_per_line; block_col++) {

            idct8x8_float(
                component.quantizationTable,
                component.blocks[block_row][block_col],
                r,
            );

            let offset = 0;
            let sample = block_col << 3;

            for (j = 0; j < 8; j++) {

                const line = lines[scan_line + j];

                for (i = 0; i < 8; i++) {
                    line[sample + i] = r[offset++];
                }

            }
        }
    }

    return lines;
}