Cannot call member function 'void TAMC_GT911::read()' without object

Well, the first problem is that the pinInt was left pulled to HIGH all the time. That's why the display was in interrupt mode all the time.

I pulled it LOW, and commented:

attachInterrupt(pinInt, onInterrupt, RISING);

And it's working. It would be nice if I can figure out re-enabling the interrupt functionality in the future, but now I'm quite happy I got it to work.

One issue I found, is that putting pinInt in input mode, locks the display in constant interrupt mode, even if I'm not enabling attachInterrupt function.

void TAMC_GT911::reset() {
  pinMode(pinInt, OUTPUT);
  pinMode(pinRst, OUTPUT);
  digitalWrite(pinInt, 0);
  digitalWrite(pinRst, 0);
  delay(10);
  digitalWrite(pinInt, 0);//addr==GT911_ADDR2
  delay(1);
  digitalWrite(pinRst, 1);
  delay(5);
  digitalWrite(pinInt, 0);
  delay(50);
  pinMode(pinInt, INPUT);
  //attachInterrupt(pinInt, onInterrupt, RISING);
  delay(50);
  readBlockData(configBuf, GT911_CONFIG_START, GT911_CONFIG_SIZE);
  setResolution(width, height);
}

So, commenting pinMode(pinInt, INPUT); leave the pinInt pulled down and problem solved.