i2c: add ShowImage() function to ssd1306 driver based on @mikegleasonjr…

… suggestion

Signed-off-by: Ron Evans <[email protected]>

drivers/i2c/ssd1306_driver.go

@@ -1,6 +1,9 @@
 package i2c
 
 import (
+	"errors"
+	"image"
+
 	"gobot.io/x/gobot"
 )
 
@@ -299,6 +302,24 @@ func (s *SSD1306Driver) Display() (err error) {
 	return err
 }
 
+// ShowImage takes a standard Go image and shows it on the display in monochrome.
+func (s *SSD1306Driver) ShowImage(img image.Image) (err error) {
+	if img.Bounds().Dx() != s.DisplayWidth || img.Bounds().Dy() != s.DisplayHeight {
+		return errors.New("Image must match the display width and height")
+	}
+
+	s.Clear()
+	for y, w, h := 0, img.Bounds().Dx(), img.Bounds().Dy(); y < h; y++ {
+		for x := 0; x < w; x++ {
+			c := img.At(x, y)
+			if r, g, b, _ := c.RGBA(); r > 0 || g > 0 || b > 0 {
+				s.Set(x, y, 1)
+			}
+		}
+	}
+	return s.Display()
+}
+
 // command sends a unique command
 func (s *SSD1306Driver) command(b byte) (err error) {
 	_, err = s.connection.Write([]byte{0x80, b})

drivers/i2c/ssd1306_driver_test.go

@@ -3,6 +3,7 @@ package i2c
 import (
 	"errors"
 	"fmt"
+	"image"
 	"reflect"
 	"strings"
 	"testing"
@@ -112,6 +113,16 @@ func TestSSD1306DriverDisplay(t *testing.T) {
 	gobottest.Assert(t, s.Display(), nil)
 }
 
+func TestSSD1306DriverShowImage(t *testing.T) {
+	s, _ := initTestSSD1306DriverWithStubbedAdaptor()
+	s.Start()
+	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
+	gobottest.Assert(t, s.ShowImage(img), errors.New("Image must match the display width and height"))
+
+	img = image.NewRGBA(image.Rect(0, 0, 128, 64))
+	gobottest.Assert(t, s.ShowImage(img), nil)
+}
+
 func TestSSD1306DriverCommand(t *testing.T) {
 	s, adaptor := initTestSSD1306DriverWithStubbedAdaptor()
 	s.Start()