M5 Paper : Unable to clear screen contents

[zitrone]

Hi folks,

I just started using M5 paper and went through the documentation at
https://docs.m5stack.com/en/api/m5paper/epd_canvas

Using this info, I created a canvas with some content in the setup.
Then, in the loop I wish to clear the canvas and display some other content.
The code is as follows :

#include <M5EPD.h>
M5EPD_Canvas canvas(&M5.EPD);
void setup() {
M5.begin(); //Init M5Paper.
M5.EPD.SetRotation(90); //Set the rotation of the display.
M5.EPD.Clear(true); //Clear the screen.
M5.RTC.begin(); //Init the RTC.

canvas.createCanvas(540, 960); //Create a canvas.
canvas.setTextSize(3); //Set the text size.
canvas.drawString("Hello World", 10, 10); //Draw a string.
canvas.pushCanvas(0,0,UPDATE_MODE_DU4); //Update the screen.
delay(2000);
}

void loop() {
M5.EPD.Clear(true); //Clear the screen.
canvas.drawString("Another string", 10, 60); //Draw a string.
canvas.pushCanvas(0,0,UPDATE_MODE_DU4); //Update the screen.
delay(5000);
}

Expected : I see only 'Another string' after refresh every 5 seconds.
Actual : Both 'Hello World' and 'Another string' are displayed.
:(

I think I am missing something. May you please explain what is going wrong here?

Thanks,
Zitrone

[felmue]

Hello @zitrone

the reason both strings are displayed is that both strings are present in the canvas which then is pushed to the screen. M5.EPD.Clear(true); only clears what is on the screen but it leaves the canvas untouched, therefore the next pushCanvas() displays both strings again on the screen.

Try adding a canvas.fillCanvas(0); after the M5.EPD.Clear(true); - this will clean the canvas (and remove the first string). See also the touch example.

BTW: you don't need the M5.EPD.Clear(true); in the loop for one string to be removed and the other to be added. (Note: w/o there might be a slight shadow where the first string was.)

Thanks
Felix

[zitrone]

@felmue Thank you for the quick reply.
Yes, it works perfectly. :)