Display.cpp

/*
 *  © 2021, Chris Harlow, Neil McKechnie. All rights reserved.
 *
 *  This file is part of CommandStation-EX
 *
 *  This is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  It is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */

// CAUTION: the device dependent parts of this class are created in the .ini
// using LCD_Implementation.h

/* The strategy for drawing the screen is as follows.
 *  1) There are up to eight rows of text to be displayed.
 *  2) Blank rows of text are ignored.
 *  3) If there are more non-blank rows than screen lines,
 *     then all of the rows are displayed, with the rest of the
 *     screen being blank.
 *  4) If there are fewer non-blank rows than screen lines,
 *     then a scrolling strategy is adopted so that, on each screen
 *     refresh, a different subset of the rows is presented.
 *  5) On each entry into loop2(), a single operation is sent to the 
 *     screen; this may be a position command or a character for
 *     display.  This spreads the onerous work of updating the screen
 *     and ensures that other loop() functions in the application are
 *     not held up significantly.  The exception to this is when 
 *     the loop2() function is called with force=true, where 
 *     a screen update is executed to completion.  This is normally
 *     only done during start-up.
 *  The scroll mode is selected by defining SCROLLMODE as 0, 1 or 2
 *  in the config.h.
 *  #define SCROLLMODE 0 is scroll continuous (fill screen if poss),
 *  #define SCROLLMODE 1 is by page (alternate between pages),
 *  #define SCROLLMODE 2 is by row (move up 1 row at a time).

 */

#include "Display.h"

// Constructor - allocates device driver.
Display::Display(DisplayDevice *deviceDriver) {
  _deviceDriver = deviceDriver;
  // Get device dimensions in characters (e.g. 16x2).
  numScreenColumns = _deviceDriver->getNumCols();
  numScreenRows = _deviceDriver->getNumRows();
  for (uint8_t row = 0; row < MAX_CHARACTER_ROWS; row++) 
    rowBuffer[row][0] = '\0';
  
  addDisplay(0);  // Add this display as display number 0
};

void Display::begin() {
  _deviceDriver->begin();
  _deviceDriver->clearNative();
}

void Display::_clear() {
  _deviceDriver->clearNative();
  for (uint8_t row = 0; row < MAX_CHARACTER_ROWS; row++) 
    rowBuffer[row][0] = '\0';
}

void Display::_setRow(uint8_t line) {
  hotRow = line;
  hotCol = 0;
  rowBuffer[hotRow][0] = '\0';  // Clear existing text
}

size_t Display::_write(uint8_t b) {
  if (hotRow >= MAX_CHARACTER_ROWS || hotCol >= MAX_CHARACTER_COLS) return -1;
  rowBuffer[hotRow][hotCol] = b;
  hotCol++;
  rowBuffer[hotRow][hotCol] = '\0';
  return 1;
}

// Refresh screen completely (will block until complete). Used
// during start-up.
void Display::_refresh() {
  loop2(true);
}

// On normal loop entries, loop will only make one output request on each
// entry, to avoid blocking while waiting for the I2C.
void Display::_displayLoop() {
  // If output device is busy, don't do anything on this loop
  // This avoids blocking while waiting for the device to complete.
  if (!_deviceDriver->isBusy()) loop2(false);
}

Display *Display::loop2(bool force) {
  unsigned long currentMillis = millis();

  if (!force) {
    // See if we're in the time between updates
    if ((currentMillis - lastScrollTime) < DISPLAY_SCROLL_TIME)
      return NULL;
  } else {
    // force full screen update from the beginning.
    rowFirst = 0;
    rowCurrent = 0;
    bufferPointer = 0;
    noMoreRowsToDisplay = false;
    slot = 0;
  }

  do {
    if (bufferPointer == 0) {
      // Search for non-blank row
      while (!noMoreRowsToDisplay) {
        if (!isCurrentRowBlank()) break;
        moveToNextRow();
        if (rowCurrent == rowFirst) noMoreRowsToDisplay = true;  
      }

      if (noMoreRowsToDisplay) {
        // No non-blank lines left, so draw blank line
        buffer[0] = '\0';
      } else {
        // Non-blank line found, so copy it (including terminator)
        for (uint8_t i = 0; i <= MAX_CHARACTER_COLS; i++)
          buffer[i] = rowBuffer[rowCurrent][i];
      }
      _deviceDriver->setRowNative(slot);  // Set position for display
      charIndex = 0;
      bufferPointer = &buffer[0];
    } else {
      // Write next character, or a space to erase current position.
      char ch = *bufferPointer;
      if (ch) {
        _deviceDriver->writeNative(ch);
        bufferPointer++;
      } else {
        _deviceDriver->writeNative(' ');
      }

      if (++charIndex >= MAX_CHARACTER_COLS) {
        // Screen slot completed, move to next nonblank row
        bufferPointer = 0;
        for (;;) {
          moveToNextRow();
          if (rowCurrent == rowFirst) {
            noMoreRowsToDisplay = true;
            break;
          }  
          if (!isCurrentRowBlank()) break;
        }
        // Move to next screen slot, if available
        slot++;
        if (slot >= numScreenRows) {
          // Last slot on screen written, so get ready for next screen update.
#if SCROLLMODE==0
          // Scrollmode 0 scrolls continuously.  If the rows fit on the screen,
          // then restart at row 0, but otherwise continue with the row
          // after the last one displayed.
          if (countNonBlankRows() <= numScreenRows)
            rowCurrent = 0;
          rowFirst = rowCurrent;
#elif SCROLLMODE==1
          // Scrollmode 1 scrolls by page, so if the last page has just completed then
          // next time restart with row 0.
          if (noMoreRowsToDisplay) 
            rowFirst = rowCurrent = 0;
#else
          // Scrollmode 2 scrolls by row.  If the rows don't fit on the screen,
          // then start one row further on next time.  If they do fit, then 
          // show them in order and start next page at row 0.
          if (countNonBlankRows() <= numScreenRows) {
            rowFirst = rowCurrent = 0;
          } else {
            // Find first non-blank row after the previous first row
            rowCurrent = rowFirst;
            do {
              moveToNextRow();
            } while (isCurrentRowBlank());
            rowFirst = rowCurrent;
          }
#endif
          noMoreRowsToDisplay = false;
          slot = 0;
          lastScrollTime = currentMillis;
          return NULL;
        }
      }
    }
  } while (force);

  return NULL;
}

bool Display::isCurrentRowBlank() {
  return (rowBuffer[rowCurrent][0] == '\0');
}

void Display::moveToNextRow() {
  // Skip blank rows
  if (++rowCurrent >= MAX_CHARACTER_ROWS) 
      rowCurrent = 0;
}

uint8_t Display::countNonBlankRows() {
  uint8_t count = 0;
  for (uint8_t rowNumber=0; rowNumber<MAX_CHARACTER_ROWS; rowNumber++) {
    if (rowBuffer[rowNumber][0] != '\0')
      count++;
  }
  return count;
}