Xteink-X4-crosspoint-reader/lib/BmpWriter/BmpWriter.h

#pragma once

#include <Print.h>

#include <cstdint>

// ============================================================================
// BMP WRITING HELPERS
// ============================================================================

// Write 16-bit value in little-endian format
inline void write16(Print& out, const uint16_t value) {
  out.write(value & 0xFF);
  out.write((value >> 8) & 0xFF);
}

// Write 32-bit unsigned value in little-endian format
inline void write32(Print& out, const uint32_t value) {
  out.write(value & 0xFF);
  out.write((value >> 8) & 0xFF);
  out.write((value >> 16) & 0xFF);
  out.write((value >> 24) & 0xFF);
}

// Write 32-bit signed value in little-endian format
inline void write32Signed(Print& out, const int32_t value) {
  out.write(value & 0xFF);
  out.write((value >> 8) & 0xFF);
  out.write((value >> 16) & 0xFF);
  out.write((value >> 24) & 0xFF);
}

// Write BMP header with 2-bit color depth (4-level grayscale)
static inline void writeBmpHeader2bit(Print& bmpOut, const int width, const int height) {
  // Calculate row padding (each row must be multiple of 4 bytes)
  const int bytesPerRow = (width * 2 + 31) / 32 * 4;  // 2 bits per pixel, round up
  const int imageSize = bytesPerRow * height;
  const uint32_t fileSize = 70 + imageSize;  // 14 (file header) + 40 (DIB header) + 16 (palette) + image

  // BMP File Header (14 bytes)
  bmpOut.write('B');
  bmpOut.write('M');
  write32(bmpOut, fileSize);  // File size
  write32(bmpOut, 0);         // Reserved
  write32(bmpOut, 70);        // Offset to pixel data

  // DIB Header (BITMAPINFOHEADER - 40 bytes)
  write32(bmpOut, 40);
  write32Signed(bmpOut, width);
  write32Signed(bmpOut, -height);  // Negative height = top-down bitmap
  write16(bmpOut, 1);              // Color planes
  write16(bmpOut, 2);              // Bits per pixel (2 bits)
  write32(bmpOut, 0);              // BI_RGB (no compression)
  write32(bmpOut, imageSize);
  write32(bmpOut, 2835);  // xPixelsPerMeter (72 DPI)
  write32(bmpOut, 2835);  // yPixelsPerMeter (72 DPI)
  write32(bmpOut, 4);     // colorsUsed
  write32(bmpOut, 4);     // colorsImportant

  // Color Palette (4 colors x 4 bytes = 16 bytes)
  // Format: Blue, Green, Red, Reserved (BGRA)
  uint8_t palette[16] = {
      0x00, 0x00, 0x00, 0x00,  // Color 0: Black
      0x55, 0x55, 0x55, 0x00,  // Color 1: Dark gray (85)
      0xAA, 0xAA, 0xAA, 0x00,  // Color 2: Light gray (170)
      0xFF, 0xFF, 0xFF, 0x00   // Color 3: White
  };
  for (const uint8_t i : palette) {
    bmpOut.write(i);
  }
}