Limitations

[Max-Headroom]

Might be worth adding this to readme:
Mentioned in FastLED_GFX.cpp line 919

// GFXcanvas1 and GFXcanvas (currently a WIP, don't get too comfy with the
// implementation) provide 1- and 16-bit offscreen canvases, the address of
// which can be passed to drawBitmap() or pushColors() (the latter appears
// to only be in Adafruit_TFTLCD at this time). This is here mostly to
// help with the recently-added proportionally-spaced fonts; adds a way to
// refresh a section of the screen without a massive flickering clear-and-
// redraw...but maybe you'll find other uses too. VERY RAM-intensive, since
// the buffer is in MCU memory and not the display driver...GXFcanvas1 might
// be minimally useful on an Uno-class board, but this and GFXcanvas are
// much more likely to require at least a Mega or various recent ARM-type
// boards (recomment, as the text+bitmap draw can be pokey). GFXcanvas1
// requires 1 bit per pixel (rounded up to nearest byte per scanline),
// GFXcanvas requires 2 bytes per pixel (no scanline pad).
// NOT EXTENSIVELY TESTED YET. MAY CONTAIN WORST BUGS KNOWN TO HUMANKIND.