st7789: add scrolling functions to match st7735

Signed-off-by: deadprogram <ron@hybridgroup.com>

st7789/registers.go

@@ -50,6 +50,8 @@ const (
 	GMCTRP1    = 0xE0
 	GMCTRN1    = 0xE1
 	GSCAN      = 0x45
+	VSCRDEF    = 0x33
+	VSCRSADD   = 0x37
 
 	NO_ROTATION  Rotation = 0
 	ROTATION_90  Rotation = 1 // 90 degrees clock-wise rotation

st7789/st7789.go

@@ -435,6 +435,27 @@ func (d *Device) IsBGR(bgr bool) {
 	d.isBGR = bgr
 }
 
+// SetScrollWindow sets an area to scroll with fixed top and bottom parts of the display
+func (d *Device) SetScrollArea(topFixedArea, bottomFixedArea int16) {
+	d.Command(VSCRDEF)
+	d.Tx([]uint8{
+		uint8(topFixedArea >> 8), uint8(topFixedArea),
+		uint8(d.height - topFixedArea - bottomFixedArea>>8), uint8(d.height - topFixedArea - bottomFixedArea),
+		uint8(bottomFixedArea >> 8), uint8(bottomFixedArea)},
+		false)
+}
+
+// SetScroll sets the vertical scroll address of the display.
+func (d *Device) SetScroll(line int16) {
+	d.Command(VSCRSADD)
+	d.Tx([]uint8{uint8(line >> 8), uint8(line)}, false)
+}
+
+// SpotScroll returns the display to its normal state
+func (d *Device) StopScroll() {
+	d.Command(NORON)
+}
+
 // RGBATo565 converts a color.RGBA to uint16 used in the display
 func RGBATo565(c color.RGBA) uint16 {
 	r, g, b, _ := c.RGBA()