microbitmatrix: add support for brightness of led pixels

Inspired by brightness levels in micro:bit MicroPython

microbitmatrix/microbitmatrix-v1.go

@@ -52,7 +52,7 @@ const (
 
 type Device struct {
 	pin      [ledCols + ledRows]machine.Pin
-	buffer   [ledRows][ledCols]bool
+	buffer   [ledRows][ledCols]int8
 	rotation uint8
 }
 

microbitmatrix/microbitmatrix-v2.go

@@ -52,7 +52,7 @@ const (
 
 type Device struct {
 	pin      [ledCols + ledRows]machine.Pin
-	buffer   [ledRows][ledCols]bool
+	buffer   [ledRows][ledCols]int8
 	rotation uint8
 }
 

microbitmatrix/microbitmatrix.go

@@ -43,20 +43,53 @@ func (d *Device) Configure(cfg Config) {
 //
 // Valid values for rotation:
 //
-//     0: regular orientation, (0 degree rotation)
+//	0: regular orientation, (0 degree rotation)
-//     1: 90 degree rotation clock wise
+//	1: 90 degree rotation clock wise
-//     2: 180 degree rotation clock wise
+//	2: 180 degree rotation clock wise
-//     3: 270 degree rotation clock wise
+//	3: 270 degree rotation clock wise
 func (d *Device) SetRotation(rotation uint8) {
 	d.rotation = rotation % 4
 }
 
+// Source:
+// https://github.com/bbcmicrobit/micropython/blob/1252f887ddc790676bf9314a136bd17650b9c36c/source/microbit/microbitdisplay.cpp#L282
+var renderTimings = []time.Duration{
+	0,  // Bright, Ticks Duration, Relative power
+	2,  //   1,   2,     32µs,     inf
+	2,  //   2,   4,     64µs,     200%
+	4,  //   3,   8,     128µs,    200%
+	7,  //   4,   15,    240µs,    187%
+	13, //   5,   28,    448µs,    187%
+	25, //   6,   53,    848µs,    189%
+	49, //   7,   102,   1632µs,   192%
+	97, //   8,   199,   3184µs,   195%
+}
+
+// Source:
+// https://github.com/bbcmicrobit/micropython/blob/1252f887ddc790676bf9314a136bd17650b9c36c/source/microbit/microbitdisplay.cpp#L368
+const tickDuration = 16 * time.Microsecond
+
 const (
 	rowIdx = 0
 	colIdx = 1
 )
 
 // SetPixel modifies the internal buffer in a single pixel.
+//
+// The alpha channel of the RGBA is used to control the brightness of the LED
+// in 9 different levels.
+//
+//	alpha channel, brightness level
+//	  0 -  27, 9 (no transparency = highest brightness)
+//	 28 -  55, 8
+//	 56 -  83, 7
+//	 84 - 111, 6
+//	112 - 139, 5
+//	140 - 167, 4
+//	168 - 195, 3
+//	196 - 223, 2
+//	224 - 251, 1 (very high transparency = lowest brightness)
+//	252 - 255, 0 (full transparency = off)
 func (d *Device) SetPixel(x int16, y int16, c color.RGBA) {
 	if x < 0 || x >= 5 || y < 0 || y >= 5 {
 		return
@@ -64,12 +97,37 @@ func (d *Device) SetPixel(x int16, y int16, c color.RGBA) {
 	col := x
 	row := y
 	if c.R != 0 || c.G != 0 || c.B != 0 {
-		d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]] = true
+		d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]] = brightness(c.A)
 	} else {
-		d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]] = false
+		d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]] = 0
 	}
 }
 
+const (
+	brightnessLevels  = 9
+	brightnessDivider = int8(255 / brightnessLevels)
+)
+
+var (
+	Brightness0 = color.RGBA{R: 0, G: 0, B: 0, A: 0}
+	Brightness1 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*1}
+	Brightness2 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*2}
+	Brightness3 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*3}
+	Brightness4 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*4}
+	Brightness5 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*5}
+	Brightness6 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*6}
+	Brightness7 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*7}
+	Brightness8 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*8}
+	Brightness9 = color.RGBA{R: 255, G: 255, B: 255, A: 255 - uint8(brightnessDivider)*9}
+
+	BrightnessOff  = Brightness0
+	BrightnessFull = Brightness9
+)
+
+func brightness(alpha uint8) int8 {
+	return brightnessLevels - int8(alpha/uint8(brightnessDivider))
+}
+
 // GetPixel returns if the specific pixels is enabled.
 func (d *Device) GetPixel(x int16, y int16) bool {
 	if x < 0 || x >= 5 || y < 0 || y >= 5 {
@@ -77,26 +135,46 @@ func (d *Device) GetPixel(x int16, y int16) bool {
 	}
 	col := x
 	row := y
-	return d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]]
+	return d.buffer[matrixRotations[d.rotation][row][col][rowIdx]][matrixRotations[d.rotation][row][col][colIdx]] > 0
 }
 
 const displayRefreshDelay = 8 * time.Millisecond
 
 // Display sends the buffer (if any) to the screen.
 func (d *Device) Display() error {
+	var displayBuffer [ledRows][ledCols]int8
+	for row := 0; row < ledRows; row++ {
+		for col := 0; col < ledCols; col++ {
+			displayBuffer[row][col] = d.buffer[row][col]
+		}
+	}
+
 	for row := 0; row < ledRows; row++ {
 		d.DisableAll()
-		d.pin[ledCols+row].Low()
+		d.pin[ledCols+row].High()
 
 		for col := 0; col < ledCols; col++ {
-			if d.buffer[row][col] {
+			if displayBuffer[row][col] > 0 {
-				d.pin[col].High()
-			} else {
 				d.pin[col].Low()
 			}
 		}
-		time.Sleep(time.Millisecond * 4)
+
+		then := time.Now()
+		var offset time.Duration = 0
+		for _, ticks := range renderTimings {
+			for time.Since(then).Nanoseconds() < int64(ticks*tickDuration+offset) {
+				time.Sleep(offset / 10)
+			}
+			offset += ticks + tickDuration
+			for col := 0; col < ledCols; col++ {
+				displayBuffer[row][col]--
+				if displayBuffer[row][col] <= 0 {
+					d.pin[col].High()
+				}
+			}
+		}
 	}
+	time.Sleep(displayRefreshDelay)
 	return nil
 }
 
@@ -104,7 +182,7 @@ func (d *Device) Display() error {
 func (d *Device) ClearDisplay() {
 	for row := 0; row < ledRows; row++ {
 		for col := 0; col < ledCols; col++ {
-			d.buffer[row][col] = false
+			d.buffer[row][col] = 0
 		}
 	}
 }