Xteink-X4-crosspoint-reader/lib/GfxRenderer/BitmapHelpers.h

#pragma once

#include <cstring>

// Helper functions
uint8_t quantize(int gray, int x, int y);
uint8_t quantizeSimple(int gray);
int adjustPixel(int gray);

// Atkinson dithering - distributes only 6/8 (75%) of error for cleaner results
// Error distribution pattern:
//     X  1/8 1/8
// 1/8 1/8 1/8
//     1/8
// Less error buildup = fewer artifacts than Floyd-Steinberg
class AtkinsonDitherer {
 public:
  AtkinsonDitherer(int width) : width(width) {
    errorRow0 = new int16_t[width + 4]();  // Current row
    errorRow1 = new int16_t[width + 4]();  // Next row
    errorRow2 = new int16_t[width + 4]();  // Row after next
  }

  ~AtkinsonDitherer() {
    delete[] errorRow0;
    delete[] errorRow1;
    delete[] errorRow2;
  }

  uint8_t processPixel(int gray, int x) {
    // Add accumulated error
    int adjusted = gray + errorRow0[x + 2];
    if (adjusted < 0) adjusted = 0;
    if (adjusted > 255) adjusted = 255;

    // Quantize to 4 levels
    uint8_t quantized;
    int quantizedValue;
    if (false) {  // original thresholds
      if (adjusted < 43) {
        quantized = 0;
        quantizedValue = 0;
      } else if (adjusted < 128) {
        quantized = 1;
        quantizedValue = 85;
      } else if (adjusted < 213) {
        quantized = 2;
        quantizedValue = 170;
      } else {
        quantized = 3;
        quantizedValue = 255;
      }
    } else {  // fine-tuned to X4 eink display
      if (adjusted < 30) {
        quantized = 0;
        quantizedValue = 15;
      } else if (adjusted < 50) {
        quantized = 1;
        quantizedValue = 30;
      } else if (adjusted < 140) {
        quantized = 2;
        quantizedValue = 80;
      } else {
        quantized = 3;
        quantizedValue = 210;
      }
    }

    // Calculate error (only distribute 6/8 = 75%)
    int error = (adjusted - quantizedValue) >> 3;  // error/8

    // Distribute 1/8 to each of 6 neighbors
    errorRow0[x + 3] += error;  // Right
    errorRow0[x + 4] += error;  // Right+1
    errorRow1[x + 1] += error;  // Bottom-left
    errorRow1[x + 2] += error;  // Bottom
    errorRow1[x + 3] += error;  // Bottom-right
    errorRow2[x + 2] += error;  // Two rows down

    return quantized;
  }

  void nextRow() {
    int16_t* temp = errorRow0;
    errorRow0 = errorRow1;
    errorRow1 = errorRow2;
    errorRow2 = temp;
    memset(errorRow2, 0, (width + 4) * sizeof(int16_t));
  }

  void reset() {
    memset(errorRow0, 0, (width + 4) * sizeof(int16_t));
    memset(errorRow1, 0, (width + 4) * sizeof(int16_t));
    memset(errorRow2, 0, (width + 4) * sizeof(int16_t));
  }

 private:
  int width;
  int16_t* errorRow0;
  int16_t* errorRow1;
  int16_t* errorRow2;
};

// Floyd-Steinberg error diffusion dithering with serpentine scanning
// Serpentine scanning alternates direction each row to reduce "worm" artifacts
// Error distribution pattern (left-to-right):
//       X   7/16
// 3/16 5/16 1/16
// Error distribution pattern (right-to-left, mirrored):
// 1/16 5/16 3/16
//      7/16  X
class FloydSteinbergDitherer {
 public:
  FloydSteinbergDitherer(int width) : width(width), rowCount(0) {
    errorCurRow = new int16_t[width + 2]();  // +2 for boundary handling
    errorNextRow = new int16_t[width + 2]();
  }

  ~FloydSteinbergDitherer() {
    delete[] errorCurRow;
    delete[] errorNextRow;
  }

  // Process a single pixel and return quantized 2-bit value
  // x is the logical x position (0 to width-1), direction handled internally
  uint8_t processPixel(int gray, int x, bool reverseDirection) {
    // Add accumulated error to this pixel
    int adjusted = gray + errorCurRow[x + 1];

    // Clamp to valid range
    if (adjusted < 0) adjusted = 0;
    if (adjusted > 255) adjusted = 255;

    // Quantize to 4 levels (0, 85, 170, 255)
    uint8_t quantized;
    int quantizedValue;
    if (false) {  // original thresholds
      if (adjusted < 43) {
        quantized = 0;
        quantizedValue = 0;
      } else if (adjusted < 128) {
        quantized = 1;
        quantizedValue = 85;
      } else if (adjusted < 213) {
        quantized = 2;
        quantizedValue = 170;
      } else {
        quantized = 3;
        quantizedValue = 255;
      }
    } else {  // fine-tuned to X4 eink display
      if (adjusted < 30) {
        quantized = 0;
        quantizedValue = 15;
      } else if (adjusted < 50) {
        quantized = 1;
        quantizedValue = 30;
      } else if (adjusted < 140) {
        quantized = 2;
        quantizedValue = 80;
      } else {
        quantized = 3;
        quantizedValue = 210;
      }
    }

    // Calculate error
    int error = adjusted - quantizedValue;

    // Distribute error to neighbors (serpentine: direction-aware)
    if (!reverseDirection) {
      // Left to right: standard distribution
      // Right: 7/16
      errorCurRow[x + 2] += (error * 7) >> 4;
      // Bottom-left: 3/16
      errorNextRow[x] += (error * 3) >> 4;
      // Bottom: 5/16
      errorNextRow[x + 1] += (error * 5) >> 4;
      // Bottom-right: 1/16
      errorNextRow[x + 2] += (error) >> 4;
    } else {
      // Right to left: mirrored distribution
      // Left: 7/16
      errorCurRow[x] += (error * 7) >> 4;
      // Bottom-right: 3/16
      errorNextRow[x + 2] += (error * 3) >> 4;
      // Bottom: 5/16
      errorNextRow[x + 1] += (error * 5) >> 4;
      // Bottom-left: 1/16
      errorNextRow[x] += (error) >> 4;
    }

    return quantized;
  }

  // Call at the end of each row to swap buffers
  void nextRow() {
    // Swap buffers
    int16_t* temp = errorCurRow;
    errorCurRow = errorNextRow;
    errorNextRow = temp;
    // Clear the next row buffer
    memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
    rowCount++;
  }

  // Check if current row should be processed in reverse
  bool isReverseRow() const { return (rowCount & 1) != 0; }

  // Reset for a new image or MCU block
  void reset() {
    memset(errorCurRow, 0, (width + 2) * sizeof(int16_t));
    memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
    rowCount = 0;
  }

 private:
  int width;
  int rowCount;
  int16_t* errorCurRow;
  int16_t* errorNextRow;
};