image: add support for image/jpeg and image/png (#303)

* Copy from go1.17 image package
* Remove unnecessary files
* Reduce memory usage
* Add examples/ili9341/slideshow
* image: add ./image/README.md
* image: change convert2bin to . /cmd
* Makefile: add ./cmd to NOTEST

examples/ili9341/slideshow/main.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"machine"
+	"strings"
+	"time"
+
+	"tinygo.org/x/drivers/ili9341"
+	"tinygo.org/x/drivers/image/jpeg"
+	"tinygo.org/x/drivers/image/png"
+)
+
+var (
+	black = color.RGBA{0, 0, 0, 255}
+	white = color.RGBA{255, 255, 255, 255}
+	red   = color.RGBA{255, 0, 0, 255}
+	blue  = color.RGBA{0, 0, 255, 255}
+	green = color.RGBA{0, 255, 0, 255}
+)
+
+func main() {
+	err := run()
+	for err != nil {
+		errorMessage(err)
+	}
+}
+
+func run() error {
+	backlight.Configure(machine.PinConfig{machine.PinOutput})
+
+	display.Configure(ili9341.Config{})
+
+	width, height := display.Size()
+	if width < 320 || height < 240 {
+		display.SetRotation(ili9341.Rotation270)
+	}
+
+	display.FillScreen(black)
+	backlight.High()
+
+	for {
+		err := drawJpeg(display)
+		if err != nil {
+			return err
+		}
+		time.Sleep(time.Second)
+
+		err = drawPng(display)
+		if err != nil {
+			return err
+		}
+		time.Sleep(time.Second)
+	}
+
+	return nil
+}
+
+// Define the buffer required for the callback. In most cases, this setting
+// should be sufficient.  For jpeg, the callback will always be called every
+// 3*8*8*4 pix. png will be called every line, i.e. every width pix.
+var buffer [3 * 8 * 8 * 4]uint16
+
+func drawPng(display *ili9341.Device) error {
+	p := strings.NewReader(pngImage)
+	png.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawPng: %s", err))
+		}
+	})
+
+	return png.Decode(p)
+}
+
+func drawJpeg(display *ili9341.Device) error {
+	p := strings.NewReader(jpegImage)
+	jpeg.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawJpeg: %s", err))
+		}
+	})
+
+	return jpeg.Decode(p)
+}
+
+func errorMessage(err error) {
+	for {
+		fmt.Printf("%s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}