ili9341: Cache address window to prevent sending unnecessary commands

[ardnew]

This is a port of an optimization recently added to the Adafruit_ILI9341 and ILI9341_t3 Arduino drivers.

It works by caching the last row/column sent to the setWindow function, and only resending the respective commands when one of the drawing axes changes. It exhibits a surprisingly effective speedup for basically all drawing operations.

Retrying PR against dev branch instead of master

[sago35]

It will be faster in normal use.
With pyportal_boing, the cache-hit rate is low, so it was not faster.
But it's not slow, so it's good.
I'd like to test it some more.

• pyportal_boing (WioTerminal (atsamd51p19 + SPI))
  • before : 40 - 42 fps
  • after : 40 - 42 fps

test code:

// setWindow prepares the screen to be modified at a given rectangle
func (d *Device) setWindow(x, y, w, h int16) {
	//x += d.columnOffset
	//y += d.rowOffset
	wr := false
	x1 := x + w - 1
	if x != d.x0 || x1 != d.x1 {
		wr = true
		d.sendCommand(CASET, []uint8{
			uint8(x >> 8), uint8(x), uint8(x1 >> 8), uint8(x1),
		})
		d.x0, d.x1 = x, x1
	}
	y1 := y + h - 1
	if y != d.y0 || y1 != d.y1 {
		wr = true
		d.sendCommand(PASET, []uint8{
			uint8(y >> 8), uint8(y), uint8(y1 >> 8), uint8(y1),
		})
		d.y0, d.y1 = y, y1
	}
	if wr {
		d.sendCommand(RAMWR, nil)
		CacheFail++ // !!!
	} else {
		CacheHit++ // !!!
	}
}

result:

41  fps
hit 25 / fail 21207

[ardnew]

Accidentally lost the hyperlinks when I copied the message from the bad PR I closed. So just for reference, the origin of the change is here:

PaulStoffregen/ILI9341_t3#59

adafruit/Adafruit_ILI9341#64

[sago35]

LGTM

[sago35]

@deadprogram
Please review.

[deadprogram]

Thanks for the contribution @ardnew and for looking it over @sago35

Now squash/merging.