ESP_8_BIT_GFX dispay missleading

Projects Programming
1

I developed on an ESP32-Wroom, a clock based on GPS. I need to display the time on two devices, an LCD and a TV screen.
I prepare 4 records containing my output. When time come I shoot my records on the LCD and on the TV screen.
I use <hd44780.h> and <hd44780ioClass/hd44780_I2Cexp.h> to manage the LCD and <ESP_8_BIT_GFX.h> to manage the TV part, inspired by hello world example.
Both displays are updated every second with exactly the same data.

Code is about 700 lines and requires a GPS module and both display
Everything look fine except the the TV display is one second after the TFT display.
I swapped the display so TV is first but that did not do any change.
When I compare the time on my PC, my phone, DC77, and LCD, all of them are in line.
Any clue ?
I ran some more tests to clearly identify the problem.
assume my code display the time every second. I observed that the LCD time is one second ahead of the TV time so I distorted the TV time and display it every 10 seconds.

    lcd.setCursor(0, 0);
    lcd.print(rec_0);

    lcd.setCursor(0, 1); 
    lcd.print(rec_1);
 
  v_ctr = v_ctr + 1;
  if (v_ctr <10) return;
  v_ctr = 0;
  // TV for the next frame to minimize chance of visible tearing
  videoOut.waitForFrame();
    // Clear screen
  videoOut.fillScreen(0);
  videoOut.setTextColor(color);
  videoOut.setTextSize(2);

  videoOut.setCursor(5, 90);
  videoOut.print(rec_0); 
  videoOut.setCursor(5, 130);
  videoOut.print(rec_1);

TV display time is 10 seconds late. When LCD time switch to 42, TV time switches to 32.

I also ran another test.
I added a statement videoOut.waitForFrame(); at the end . Both times on LCD and on TV where identical but the image was tearing.
This issue is not visible in the example Hello world as the code is continuously looping.

Temporary fix, efficient but not really smart:
I simply duplicated the write sequence.

2

What happens if you call waitForFrame() both before and after updating the output?

I notice the following on the libraries github page:

This implies that when you output the time to the video display, it is written to the "back" buffer, but this buffer is not actually displayed until the next call to waitForFrame(), which occurs a second later.

3

When print() stmt are followed by waitForFrame(), the buffer is immediately written to the screen. This solves the issue.

4

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