ili9341: st7735: st7789: unify rotation support

* Unify the Rotation type, so that SetRotation can be used in
    interfaces.
  * Add Rotation() method to these displays, so that the current
    rotation can be read.
  * Change SetRotation() so that it can return an error (if the given
    rotation isn't supported).

st7735/st7735.go

@@ -14,7 +14,11 @@ import (
 )
 
 type Model uint8
-type Rotation uint8
+
+// Rotation controls the rotation used by the display.
+//
+// Deprecated: use drivers.Rotation instead.
+type Rotation = drivers.Rotation
 
 var (
 	errOutOfBounds = errors.New("rectangle coordinates outside display area")
@@ -31,7 +35,7 @@ type Device struct {
 	height       int16
 	columnOffset int16
 	rowOffset    int16
-	rotation     Rotation
+	rotation     drivers.Rotation
 	batchLength  int16
 	model        Model
 	isBGR        bool
@@ -42,7 +46,7 @@ type Device struct {
 type Config struct {
 	Width        int16
 	Height       int16
-	Rotation     Rotation
+	Rotation     drivers.Rotation
 	Model        Model
 	RowOffset    int16
 	ColumnOffset int16
@@ -215,7 +219,7 @@ func (d *Device) SetPixel(x int16, y int16, c color.RGBA) {
 
 // setWindow prepares the screen to be modified at a given rectangle
 func (d *Device) setWindow(x, y, w, h int16) {
-	if d.rotation == NO_ROTATION || d.rotation == ROTATION_180 {
+	if d.rotation == drivers.Rotation0 || d.rotation == drivers.Rotation180 {
 		x += d.columnOffset
 		y += d.rowOffset
 	} else {
@@ -345,35 +349,38 @@ func (d *Device) DrawFastHLine(x0, x1, y int16, c color.RGBA) {
 
 // FillScreen fills the screen with a given color
 func (d *Device) FillScreen(c color.RGBA) {
-	if d.rotation == NO_ROTATION || d.rotation == ROTATION_180 {
+	if d.rotation == drivers.Rotation0 || d.rotation == drivers.Rotation180 {
 		d.FillRectangle(0, 0, d.width, d.height, c)
 	} else {
 		d.FillRectangle(0, 0, d.height, d.width, c)
 	}
 }
 
+// Rotation returns the currently configured rotation.
+func (d *Device) Rotation() drivers.Rotation {
+	return d.rotation
+}
+
 // SetRotation changes the rotation of the device (clock-wise)
-func (d *Device) SetRotation(rotation Rotation) {
+func (d *Device) SetRotation(rotation drivers.Rotation) error {
+	d.rotation = rotation
 	madctl := uint8(0)
 	switch rotation % 4 {
-	case 0:
+	case drivers.Rotation0:
 		madctl = MADCTL_MX | MADCTL_MY
-		break
-	case 1:
+	case drivers.Rotation90:
 		madctl = MADCTL_MY | MADCTL_MV
-		break
-	case 2:
-		break
-	case 3:
+	case drivers.Rotation180:
+		// nothing to do
+	case drivers.Rotation270:
 		madctl = MADCTL_MX | MADCTL_MV
-		break
 	}
 	if d.isBGR {
 		madctl |= MADCTL_BGR
 	}
 	d.Command(MADCTL)
 	d.Data(madctl)
-
+	return nil
 }
 
 // Command sends a command to the display
@@ -394,7 +401,7 @@ func (d *Device) Tx(data []byte, isCommand bool) {
 
 // Size returns the current size of the display.
 func (d *Device) Size() (w, h int16) {
-	if d.rotation == NO_ROTATION || d.rotation == ROTATION_180 {
+	if d.rotation == drivers.Rotation0 || d.rotation == drivers.Rotation180 {
 		return d.width, d.height
 	}
 	return d.height, d.width