How does JPEGDecoder work on the sprite of tft espi?

[fzzdcode]

How does JPEGDecoder work on the sprite of tft espi?
TFT_eSprite spr=TFT_eSprite (&tft);

Void loop()
{
spr. fillSprite(TFT_RED);

spr. pushImage (191,0, jpgDecoder_buff); <== How does it work here?

spr. pushSpite (0,0);
delay (1);
}