Led Matrix : random bits on lines or columns

[paulvha]

When using ArduinoGraphics on the Led Matrix and doing a scroll left random bits are showing in the RIGHT columns. This is happening as well when doing a scroll up, on the bottom lines.

It was noticed already doing development given the remark in the function endDraw() in Arduino_LED_matrix.h:

ArduinoCore-renesas/libraries/Arduino_LED_Matrix/src/Arduino_LED_Matrix.h

Line 266 in 6ee152f

// clear first line (no idea why it gets filled with random bits, probably some math not working fine for super small displays)

The root cause is related to ArduinoGraphics as it returns NEGATIVE numbers when scrolling. In the function set() in Arduino_led_matrix.h it checks for out of bound values, BUT not for negative values for Y and X. Then when doing a _canvasBuffer[y][x] will cause under desired memory to be written.

Solution :

change in function set(), line 251 from:

ArduinoCore-renesas/libraries/Arduino_LED_Matrix/src/Arduino_LED_Matrix.h

Line 251 in 6ee152f

if (y >= canvasHeight || x >= canvasWidth) {

to:

if (y >= canvasHeight || x >= canvasWidth || y < 0 || x < 0) {

[aentinger]

Hi @paulvha ☕ 👋

Thank you for reporting this issue. I've been able to verify it with this minimal example sketch:

// To use ArduinoGraphics APIs, please include BEFORE Arduino_LED_Matrix
#include "ArduinoGraphics.h"
#include "Arduino_LED_Matrix.h"

ArduinoLEDMatrix matrix;

void setup() {
  Serial.begin(115200);
  matrix.begin();

  matrix.textScrollSpeed(50);

  matrix.beginDraw();
  matrix.stroke(0xFFFFFFFF);

  const char text[] = "UNO r4";
  matrix.textFont(Font_4x6);
  matrix.beginText(0, 1, 0xFFFFFF);
  matrix.println(text);
  matrix.endText(SCROLL_LEFT);

  matrix.endDraw();

  delay(2000);
}

void loop() {
}

I can confirm that your suggestion is fixing this issue and I will be preparing a PR for it.