flipDMABuffer - What am I doing wrong?

[mcgalactor]

Hi,

I'm trying to reduce flickering using flipDMABuffer. From what I understand, I can disconnect (flip#1) the buffer from the output (sending it to the back), do some heavy calculations for the new output, and then reconnect it (flip#2). I've simplified the problem in the following test sketch. Why am I seeing the "Temp Output" on the display? Wasn't it supposed to go to the back buffer?
I read this thread:
flipDMABuffer without flipping the target buffer
I understand I should see a blank buffer after flipping but I still see the "Temp Output".

Thanks

Jan

PS: Thank you for providing this library; it greatly simplifies my project.

#include <ESP32-HUB75-MatrixPanel-I2S-DMA.h>
MatrixPanel_I2S_DMA *display = nullptr;

const int panelResX = 64; // Number of pixels wide of each INDIVIDUAL panel module.
const int panelResY = 32; // Number of pixels tall of each INDIVIDUAL panel module.
const int panel_chain = 2; // Total number of panels chained one to another
void drawHeavyStuff();

#define PANEL_RES_X 64 // Number of pixels wide of each INDIVIDUAL panel module.
#define PANEL_RES_Y 32 // Number of pixels tall of each INDIVIDUAL panel module.

void setup()
{
// put your setup code here, to run once:
delay(1000);
Serial.begin(115200);
delay(200);

#define R1_PIN 25
#define G1_PIN 27
#define B1_PIN 26
#define R2_PIN 14
#define G2_PIN 13
#define B2_PIN 12
#define A_PIN 22
#define B_PIN 19
#define C_PIN 18
#define D_PIN 5
#define E_PIN 23 // required for 1/32 scan panels, like 64x64px. Any available pin would do, i.e. IO32
#define LAT_PIN 2
#define OE_PIN 15
#define CLK_PIN 4

HUB75_I2S_CFG::i2s_pins _pins = {R1_PIN, G1_PIN, B1_PIN, R2_PIN, G2_PIN, B2_PIN, A_PIN, B_PIN, C_PIN, D_PIN, E_PIN, LAT_PIN, OE_PIN, CLK_PIN};
HUB75_I2S_CFG mxconfig(/* width = / panelResX, / height = / panelResY, / chain = */ panel_chain, _pins);

display = new MatrixPanel_I2S_DMA(mxconfig);
mxconfig.double_buff = true; // <------------- Turn on double buffer

display->begin();
display->setBrightness8(255);
display->setTextSize(4);
drawHeavyStuff();
}

void drawHeavyStuff()
{
display->flipDMABuffer(); //flip#1; disconnect output buffer (send it to the back)
display->clearScreen(); //clear back buffer
for (int i = 0; i < 64; i++) //simulating heavy calculations
{
display->setCursor(i, 0);
display->print("Temp Output"); // not supposed to be seen, since it is printed to the back buffer
delay(40);
display->clearScreen(); //clear back buffer
}

display->setCursor(0, 0);
display->print("Final Output"); //print final output
display->flipDMABuffer();//flip#2; flip buffer to see "Final Output"
}

void loop()
{

delay(1000);

}

[mcgalactor]

Found it!

The initialization of the double buffer was not done correctly.
After I fixed it, flipping works like a charm. No more flickering.