Added position offset to playSDraw

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also here is a function to generate a reversed copy of a file (should be small file dont get crazy now, takes a bit to render the reversed version)


Code: 
void reverseFile(char *from, char *to)
{
  long infile_offset;
  int bytes_read;
  uint16_t data[512];
  File fh_in;
  File fh_out;
  char debug[128];
  
  Serial.println("removing");
  if (SD.exists(to)) {SD.remove(to);}

  Serial.println("opening");
  fh_in = SD.open(from, FILE_READ);
  fh_out = SD.open(to, FILE_WRITE);

  Serial.println("generating debug string");
  sprintf(debug, "Reversing file %s, length %d\n", from, fh_in.size());
  Serial.println(debug);

  infile_offset = (fh_in.size()/512)*512; /* should truncate to 512-byte boundary */
  while (infile_offset >= 0) {    
    fh_in.seek(infile_offset);
    bytes_read = fh_in.read(data, 512);
    reverseMem((uint16_t*)data, bytes_read/2);
    // sprintf(debug, "%d -> %d", infile_offset, fh_out.position());
    // Serial.println(debug);
    fh_out.write((char *)data, bytes_read);
    infile_offset -= 512;
    }
  Serial.println("done");
  fh_out.close();
  fh_in.close();
}

void reverseMem(uint16_t *data, int sampleCount)
{
  int i;
  uint16_t tmp;
  
  for (i=0; i<sampleCount/2-1; i++) {
    tmp = data[i];
    data[i] = data[sampleCount-i-1];
    data[sampleCount-i-1] = tmp;
    }
}
 
It looks like receter posted some good stuff on the granular thread, I think you should actually adapt his loop object into the main play, but just have a loop enable

it would be nice to have the loop start and end locked to nearest zero crossing as an option
it could be useful to have a separate play start and play end variable so you can play a sound and have it start looping at a certain point after the beginning if wanted.
 
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