ili9341: add EnableTEOutput to be able to sync drawing with VSYNC

Many displays don't have the TE pin exposed. But those that do have the
pin (for example, the PyPortal) can use it to synchronize writing a new
image to the display. When implemented correctly, tearing can be avoided
entirely.

This commit also changes the LCD refresh direction to either
top-to-bottom or left-to-right depending on the rotation. Previously it
might refresh from right-to-left or bottom-to-top. This has little
impact on code that doesn't use the TE line, but code that does now only
needs to worry about two cases (top-to-bottom and left-to-right) instead
of four.
(Unfortunately, it appears that the hardware doesn't support changing
the major LCD refresh order so code that wants to do tear-free rendering
still needs to care about these two cases).

ili9341/ili9341.go

@@ -160,6 +160,18 @@ func (d *Device) Display() error {
 	return nil
 }
 
+// EnableTEOutput enables the TE ("tearing effect") line.
+// The TE line goes high when the screen is not currently being updated and can
+// be used to start drawing. When used correctly, it can avoid tearing entirely.
+func (d *Device) EnableTEOutput(on bool) {
+	if on {
+		cmdBuf[0] = 0
+		d.sendCommand(TEON, cmdBuf[:1]) // M=0 (V-blanking only, no H-blanking)
+	} else {
+		d.sendCommand(TEOFF, nil) // TEOFF
+	}
+}
+
 // DrawRGBBitmap copies an RGB bitmap to the internal buffer at given coordinates
 func (d *Device) DrawRGBBitmap(x, y int16, data []uint16, w, h int16) error {
 	k, i := d.Size()
@@ -287,17 +299,17 @@ func (d *Device) SetRotation(rotation drivers.Rotation) error {
 	case Rotation90:
 		madctl = MADCTL_MV | MADCTL_BGR
 	case Rotation180:
-		madctl = MADCTL_MY | MADCTL_BGR
+		madctl = MADCTL_MY | MADCTL_BGR | MADCTL_ML
 	case Rotation270:
-		madctl = MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR
+		madctl = MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR | MADCTL_ML
 	case Rotation0Mirror:
 		madctl = MADCTL_BGR
 	case Rotation90Mirror:
-		madctl = MADCTL_MY | MADCTL_MV | MADCTL_BGR
+		madctl = MADCTL_MY | MADCTL_MV | MADCTL_BGR | MADCTL_ML
 	case Rotation180Mirror:
-		madctl = MADCTL_MX | MADCTL_MY | MADCTL_BGR
+		madctl = MADCTL_MX | MADCTL_MY | MADCTL_BGR | MADCTL_ML
 	case Rotation270Mirror:
-		madctl = MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR
+		madctl = MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR | MADCTL_ML
 	}
 	cmdBuf[0] = madctl
 	d.sendCommand(MADCTL, cmdBuf[:1])

ili9341/registers.go

@@ -41,6 +41,8 @@ const (
 
 	PTLAR    = 0x30 ///< Partial Area
 	VSCRDEF  = 0x33 ///< Vertical Scrolling Definition
+	TEOFF    = 0x34 ///< TEOFF: Tearing Effect Line OFF
+	TEON     = 0x35 ///< TEON: Tearing Effect Line ON
 	MADCTL   = 0x36 ///< Memory Access Control
 	VSCRSADD = 0x37 ///< Vertical Scrolling Start Address
 	PIXFMT   = 0x3A ///< COLMOD: Pixel Format Set