Fix: do not crash on ASCII chars with a numeric value exceeding 127.

[aentinger]

When writing a text this library supports 255 different characters. However, due to the function signature of ArduinoGraphics::text(const char* str, ... which passes a const char* value is interpreted as a negative value when a ASCII character with a numeric value exceeding 127 is passed to this function. Subsequently this leads to an array out-of-bounds access and a application crash.

By casting to uint8_t we ensure that we obtain the correct (positive) numeric value for subsequently accessing the bitmap without array-out-of-bounds access.

Minimal failing test application (crashes upon execution):

#include "ArduinoGraphics.h"
#include "Arduino_LED_Matrix.h"

ArduinoLEDMatrix matrix;

void setup()
{
  matrix.begin();

  float const temperature = 25.3f;
  float const humidity = 47.6f;
  float const pressure = 1.23f;

  char msg[64] = {0};
  snprintf(msg, sizeof(msg), "%0.1f °C, %0.1f %%, %0.2f atm", temperature, humidity, pressure);

  matrix.beginDraw();

  matrix.stroke(0xFFFFFFFF);
  matrix.textScrollSpeed(80);

  matrix.textFont(Font_5x7);
  matrix.beginText(0, 1, 0xFFFFFF);
  matrix.println(msg);
  matrix.endText(SCROLL_LEFT);

  matrix.endDraw();
}

[github-actions]

Memory usage change @ 6cafff9

Board	flash	%	RAM for global variables	%
arduino:samd:arduino_zero_edbg	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrzero	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:nano_33_iot	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/ASCIIDraw flash	%	examples/ASCIIDraw RAM for global variables	%
arduino:samd:arduino_zero_edbg	0	0.0	0	0.0
arduino:samd:mkrzero	0	0.0	0	0.0
arduino:samd:nano_33_iot	0	0.0	0	0.0

Click for full report CSV

Board,examples/ASCIIDraw<br>flash,%,examples/ASCIIDraw<br>RAM for global variables,%
arduino:samd:arduino_zero_edbg,0,0.0,0,0.0
arduino:samd:mkrzero,0,0.0,0,0.0
arduino:samd:nano_33_iot,0,0.0,0,0.0

[aentinger]

output.mp4