niimblue-nightly/niimbluelib/src/image_encoder.ts

import { Utils } from "./utils";

export type ImageRow = {
  dataType: "void" | "pixels";
  rowNumber: number;
  repeat: number;
  blackPixelsCount: number;
  rowData?: Uint8Array;
};

export type EncodedImage = {
  cols: number;
  rows: number;
  rowsData: ImageRow[];
};

export type HeadPosition = "left" | "top";

export class ImageEncoder {
  /** headPos = "left" rotates image for 90 degrees clockwise */
  public static encodeCanvas(canvas: HTMLCanvasElement, headPos: HeadPosition = "left"): EncodedImage {
    const ctx: CanvasRenderingContext2D = canvas.getContext("2d")!;
    const iData: ImageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    const rowsData: ImageRow[] = [];

    let cols: number = canvas.width;
    let rows: number = canvas.height;

    if (headPos === "left") {
      cols = canvas.height;
      rows = canvas.width;
    }

    if (cols % 8 !== 0) {
      throw new Error("Column count must be multiple of 8");
    }

    for (let row = 0; row < rows; row++) {
      let isVoid: boolean = true;
      let blackPixelsCount: number = 0;
      const rowData = new Uint8Array(cols / 8);

      for (let colOct = 0; colOct < cols / 8; colOct++) {
        let pixelsOctet: number = 0;
        for (let colBit = 0; colBit < 8; colBit++) {
          if (ImageEncoder.isPixelNonWhite(iData, colOct * 8 + colBit, row, headPos)) {
            pixelsOctet |= 1 << (7 - colBit);
            isVoid = false;
            blackPixelsCount++;
          }
        }
        rowData[colOct] = pixelsOctet;
      }

      const newPart: ImageRow = {
        dataType: isVoid ? "void" : "pixels",
        rowNumber: row,
        repeat: 1,
        rowData: isVoid ? undefined : rowData,
        blackPixelsCount,
      };

      // Check previous row and increment repeats instead of adding new row if data is same
      if (rowsData.length === 0) {
        rowsData.push(newPart);
      } else {
        const lastPacket: ImageRow = rowsData[rowsData.length - 1];
        let same: boolean = newPart.dataType === lastPacket.dataType;

        if (same && newPart.dataType === "pixels") {
          same = Utils.u8ArraysEqual(newPart.rowData!, lastPacket.rowData!);
        }

        if (same) {
          lastPacket.repeat++;
        } else {
          rowsData.push(newPart);
        }
      }
    }

    return { cols, rows, rowsData };
  }

  /** headPos = "left" rotates image to 90 degrees clockwise */
  public static isPixelNonWhite(iData: ImageData, x: number, y: number, headPos: HeadPosition = "left"): boolean {
    let idx = y * iData.width + x;

    if (headPos === "left") {
      idx = (iData.height - 1 - x) * iData.width + y;
    }

    idx *= 4;
    return iData.data[idx] !== 255 || iData.data[idx + 1] !== 255 || iData.data[idx + 2] !== 255;
  }

  /**
   * @param data Encoded pixels (every byte is 8 pixels)
   * @returns Array of indexes where every index stored in two bytes (big endian)
   */
  public static indexPixels(data: Uint8Array): Uint8Array {
    const result: number[] = [];

    for (let bytePos = 0; bytePos < data.byteLength; bytePos++) {
      let b: number = data[bytePos];
      for (let bitPos = 0; bitPos < 8; bitPos++) {
        // iterate from most significant bit of byte
        if (b & (1 << (7 - bitPos))) {
          result.push(...Utils.u16ToBytes(bytePos * 8 + bitPos));
        }
      }
    }

    return new Uint8Array(result);
  }
}