Fast partial refresh GDEW075Z08 b/w/r

[ammmec]

Hi! I am using the Waveshare 7.5'' b/w/r display (GDEW075Z08) with a Firebeetle 2 ESP32-C6 for a battery-powered project. I have noticed that the partial refresh, which takes less than 2 seconds in the Waveshare library, takes as long as the full refresh in your library. I assume that some models have support for a faster partial refresh, like in the FastBlackWhiteOnColor example. So, would it be possible to adapt the library so that the GDEW075Z08 can also do a quick b/w partial refresh?

[ZinggJM]

Yes, it is possible. This display has true partial window refresh. I will consider to add it when I have time for it.

[ammmec]

Thank you for considering it! And also thanks for all the work you've done with the library, it is a great help and it is much easier to navigate than the other libraries.

[aceisace]

Thank you very much for your time writing up this awesome library in your free time @ZinggJM !
Really appreciate what you are doing here, not only in terms of the software, but also the top-notch support, thank you very much for that 😄

I am also eagerly waiting with my hands crossed when this feature will be available in the mainstream. I did take a look at the GxEPD2_213_Z19c file, which seems to be used as a reference for this feature, but I'm really not an expert in cpp

Just a few things to make the implementation as easy as possible, as your time is precious:

• link to waveshare's driver file which seems to have support for fast bw-rendering for the GDEW075Z08 display: Waveshare 7.3" 800x480 b-v2 driver

Missing implementations, which can probably be copy-pasted from GxEPD2_213_Z19c drivers:

class GxEPD2_750c_Z08 : public GxEPD2_EPD
{
  public:
    void writeImageNew(const uint8_t* black, int16_t x, int16_t y, int16_t w, int16_t h, bool invert = false, bool mirror_y = false, bool pgm = false);
    void writeImagePrevious(const uint8_t* black, int16_t x, int16_t y, int16_t w, int16_t h, bool invert = false, bool mirror_y = false, bool pgm = false);
    void writeImagePartNew(const uint8_t* black, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap, int16_t x, int16_t y, int16_t w, int16_t h, bool invert = false, bool mirror_y = false, bool pgm = false);
    void writeImagePartPrevious(const uint8_t* black, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap, int16_t x, int16_t y, int16_t w, int16_t h, bool invert = false, bool mirror_y = false, bool pgm = false);
    void refresh_bw(int16_t x, int16_t y, int16_t w, int16_t h);
private:
    void _writeImage(uint8_t command, const uint8_t* bitmap, int16_t x, int16_t y, int16_t w, int16_t h,  bool invert, bool mirror_y, bool pgm);             
    void _writeImagePart(uint8_t command, const uint8_t* bitmap, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap, int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm);
}

My take on the implementation of said functions in he GxEPD2_750c_Z08.cpp file, please take with a grain of salt, I am by no means a professional cpp developer:

void GxEPD2_750c_Z08::_writeImage(uint8_t command, const uint8_t* bitmap, int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  if (_initial_write) writeScreenBuffer(); // initial full screen buffer clean
  delay(1); // yield() to avoid WDT on ESP8266 and ESP32
  int16_t wb = (w + 7) / 8; // width bytes, bitmaps are padded
  x -= x % 8; // byte boundary
  w = wb * 8; // byte boundary
  int16_t x1 = x < 0 ? 0 : x; // limit
  int16_t y1 = y < 0 ? 0 : y; // limit
  int16_t w1 = x + w < int16_t(WIDTH) ? w : int16_t(WIDTH) - x; // limit
  int16_t h1 = y + h < int16_t(HEIGHT) ? h : int16_t(HEIGHT) - y; // limit
  int16_t dx = x1 - x;
  int16_t dy = y1 - y;
  w1 -= dx;
  h1 -= dy;
  if ((w1 <= 0) || (h1 <= 0)) return;
  _Init_Part();
  _writeCommand(0x91); // partial in
  _setPartialRamArea(x1, y1, w1, h1);
  _writeCommand(command);
  for (int16_t i = 0; i < h1; i++)
  {
    for (int16_t j = 0; j < w1 / 8; j++)
    {
      uint8_t data = 0xFF;
      if (bitmap)
      {
        // use wb, h of bitmap for index!
        int16_t idx = mirror_y ? j + dx / 8 + ((h - 1 - (i + dy))) * wb : j + dx / 8 + (i + dy) * wb;
        if (pgm)
        {
#if defined(__AVR) || defined(ESP8266) || defined(ESP32)
          data = pgm_read_byte(&bitmap[idx]);
#else
          data = bitmap[idx];
#endif
        }
        else
        {
          data = bitmap[idx];
        }
        if (invert) data = ~data;
      }
      _writeData(data);
    }
  }
  _writeCommand(0x92); // partial out
  delay(1); // yield() to avoid WDT on ESP8266 and ESP32
}

void GxEPD2_750c_Z08::_writeImagePart(uint8_t command, const uint8_t* bitmap, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap,
                                      int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  if (_initial_write) writeScreenBuffer(); // initial full screen buffer clean
  delay(1); // yield() to avoid WDT on ESP8266 and ESP32
  if ((w_bitmap < 0) || (h_bitmap < 0) || (w < 0) || (h < 0)) return;
  if ((x_part < 0) || (x_part >= w_bitmap)) return;
  if ((y_part < 0) || (y_part >= h_bitmap)) return;
  int16_t wb_bitmap = (w_bitmap + 7) / 8; // width bytes, bitmaps are padded
  x_part -= x_part % 8; // byte boundary
  w = w_bitmap - x_part < w ? w_bitmap - x_part : w; // limit
  h = h_bitmap - y_part < h ? h_bitmap - y_part : h; // limit
  x -= x % 8; // byte boundary
  w = 8 * ((w + 7) / 8); // byte boundary, bitmaps are padded
  int16_t x1 = x < 0 ? 0 : x; // limit
  int16_t y1 = y < 0 ? 0 : y; // limit
  int16_t w1 = x + w < int16_t(WIDTH) ? w : int16_t(WIDTH) - x; // limit
  int16_t h1 = y + h < int16_t(HEIGHT) ? h : int16_t(HEIGHT) - y; // limit
  int16_t dx = x1 - x;
  int16_t dy = y1 - y;
  w1 -= dx;
  h1 -= dy;
  if ((w1 <= 0) || (h1 <= 0)) return;
  if (!_using_partial_mode) _Init_Part();
  _writeCommand(0x91); // partial in
  _setPartialRamArea(x1, y1, w1, h1);
  _writeCommand(command);
  for (int16_t i = 0; i < h1; i++)
  {
    for (int16_t j = 0; j < w1 / 8; j++)
    {
      uint8_t data;
      // use wb_bitmap, h_bitmap of bitmap for index!
      int16_t idx = mirror_y ? x_part / 8 + j + dx / 8 + ((h_bitmap - 1 - (y_part + i + dy))) * wb_bitmap : x_part / 8 + j + dx / 8 + (y_part + i + dy) * wb_bitmap;
      if (pgm)
      {
#if defined(__AVR) || defined(ESP8266) || defined(ESP32)
        data = pgm_read_byte(&bitmap[idx]);
#else
        data = bitmap[idx];
#endif
      }
      else
      {
        data = bitmap[idx];
      }
      if (invert) data = ~data;
      _writeData(data);
    }
  }
  _writeCommand(0x92); // partial out
  delay(1); // yield() to avoid WDT on ESP8266 and ESP32
}

void GxEPD2_750c_Z08::writeImageNew(const uint8_t* black, int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  _writeImage(0x13, black, x, y, w, h, invert, mirror_y, pgm);
}
void GxEPD2_750c_Z08::writeImagePrevious(const uint8_t* black, int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  _writeImage(0x10, black, x, y, w, h, invert, mirror_y, pgm);
}

void GxEPD2_750c_Z08::writeImagePartNew(const uint8_t* black, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap,
                                        int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  _writeImagePart(0x13, black, x_part, y_part, w_bitmap, h_bitmap, x, y, w, h, invert, mirror_y, pgm);
}

void GxEPD2_750c_Z08::writeImagePartPrevious(const uint8_t* black, int16_t x_part, int16_t y_part, int16_t w_bitmap, int16_t h_bitmap,
    int16_t x, int16_t y, int16_t w, int16_t h, bool invert, bool mirror_y, bool pgm)
{
  _writeImagePart(0x10, black, x_part, y_part, w_bitmap, h_bitmap, x, y, w, h, invert, mirror_y, pgm);
}

void GxEPD2_750c_Z08::refresh_bw(int16_t x, int16_t y, int16_t w, int16_t h)
{
  x -= x % 8;
  w += (8 - (w % 8)) % 8;

  int16_t x1 = x < 0 ? 0 : x;
  int16_t y1 = y < 0 ? 0 : y;
  int16_t w1 = (x + w < int16_t(WIDTH)) ? w : int16_t(WIDTH) - x;
  int16_t h1 = (y + h < int16_t(HEIGHT)) ? h : int16_t(HEIGHT) - y;

  if ((w1 <= 0) || (h1 <= 0)) return;

  _Init_Part();

  _writeCommand(0x91); // partial in
  _setPartialRamArea(x1, y1, w1, h1);
  _Update_Part();
  _writeCommand(0x92); // partial out
}

A working example to test this out would be awesome 🙏
If you need any help from my side for code testing, I am up for it 👍