matemat/uncanny/display.go

package uncanny

import (
	"errors"
	"fmt"
	"golang.org/x/text/encoding/charmap"
)

// min returns the smaller of two integers {
func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

// max returns the larger of two integers {
func max(x, y int) int {
	if x > y {
		return x
	}
	return y
}

// encodeString encodes a Unicode string into a given charmap.
// Unsupported characters are replaced by the default replacement symbol.
// Mysteriously, this functionality is missing from x/text/encoding.
// TODO Implement the custom NEC display encoding.
func encodeString(s string) ([]byte) {
	ret := make([]byte, len(s))
	for i, c := range(s) {
		ret[i], _ = charmap.ISO8859_1.EncodeRune(c)
	}
	return ret
}

func (c *Can) DisplayWrite(line int, a []byte) error {
	var addr int
	switch line {
	case 0:
		addr = 0x80
	case 1:
		addr = 0xc0
	default:
		return errors.New("Invalid line")
	}
	// print in separate chunks, as one frame payload is limited to 7 bytes
	// the display has only 16 characters per line, so we truncate there
	for i := 0; i < min(len(a), 16); i += 7 {
		err := c.bus.Publish(DisplayCommand{addr + i, a[i:min(i+7,len(a))]}.Encode())
		if err != nil {
			return err
		}
	}
	return nil
}

func (c *Can) DisplayPrint(line int, a string) error {
	return c.DisplayWrite(line, encodeString(a))
}

func (c *Can) DisplayPrintf(line int, a string, args ...interface{}) error {
	s := fmt.Sprintf(a, args...)
	return c.DisplayPrint(line, s)
}