From 2fa57a73a16d78cc1c7bae48b85e053eb6bff877 Mon Sep 17 00:00:00 2001
From: Gabriel Augendre <gabriel@augendre.info>
Date: Mon, 16 Sep 2024 18:09:00 +0200
Subject: [PATCH] refresh only when image changes

---
 img.go              |  2 +-
 main.go             |  2 +-
 run_darwin_arm64.go |  2 +-
 run_linux_arm64.go  | 49 +++++++++++++++++++++++++++++++++------------
 4 files changed, 39 insertions(+), 16 deletions(-)

diff --git a/img.go b/img.go
index cfaad76..34f25bf 100644
--- a/img.go
+++ b/img.go
@@ -29,7 +29,7 @@ const (
 	rightX = 530
 )
 
-func getBlack(
+func getImg(
 	ctx context.Context,
 	nowFunc func() time.Time,
 	transportsClient *transports.Client,
diff --git a/main.go b/main.go
index bd7246f..97453eb 100644
--- a/main.go
+++ b/main.go
@@ -41,7 +41,7 @@ func main() {
 		CacheLocation: os.Getenv("WEATHER_CACHE_LOCATION"),
 	})
 
-	const minSleep = 30 * time.Second
+	const minSleep = 1 * time.Second
 
 	sleep, err := time.ParseDuration(os.Getenv("SLEEP_DURATION"))
 	if err != nil || sleep < minSleep {
diff --git a/run_darwin_arm64.go b/run_darwin_arm64.go
index 80bd6e8..1a5e2fc 100644
--- a/run_darwin_arm64.go
+++ b/run_darwin_arm64.go
@@ -17,7 +17,7 @@ func run(
 	feteClient *fete.Client,
 	weatherClient *weather.Client,
 ) error {
-	img, err := getBlack(
+	img, err := getImg(
 		ctx,
 		func() time.Time {
 			t, err := time.Parse(time.DateOnly, "2024-08-01zzz")
diff --git a/run_linux_arm64.go b/run_linux_arm64.go
index b64e2da..25fbbc9 100644
--- a/run_linux_arm64.go
+++ b/run_linux_arm64.go
@@ -7,6 +7,7 @@ import (
 	"github.com/Crocmagnon/display-epaper/fete"
 	"github.com/Crocmagnon/display-epaper/transports"
 	"github.com/Crocmagnon/display-epaper/weather"
+	"image"
 	"log"
 	"os"
 	"periph.io/x/host/v3"
@@ -30,6 +31,8 @@ func run(
 		return fmt.Errorf("initializing epd: %w", err)
 	}
 
+	var currentImg image.Image
+
 	for {
 		select {
 		case <-ctx.Done():
@@ -40,9 +43,10 @@ func run(
 
 		log.Println("running loop")
 
-		err = loop(
+		img, err := loop(
 			ctx,
 			display,
+			currentImg,
 			transportsClient,
 			feteClient,
 			weatherClient,
@@ -51,19 +55,15 @@ func run(
 			log.Printf("error looping: %v\n", err)
 		}
 
+		currentImg = img
+
 		log.Printf("time.Sleep(%v)\n", sleep)
 		time.Sleep(sleep)
 	}
 }
 
-func loop(
-	ctx context.Context,
-	display *epd.EPD,
-	transportsClient *transports.Client,
-	feteClient *fete.Client,
-	weatherClient *weather.Client,
-) error {
-	black, err := getBlack(
+func loop(ctx context.Context, display *epd.EPD, currentImg image.Image, transportsClient *transports.Client, feteClient *fete.Client, weatherClient *weather.Client) (image.Image, error) {
+	img, err := getImg(
 		ctx,
 		time.Now,
 		transportsClient,
@@ -71,7 +71,12 @@ func loop(
 		weatherClient,
 	)
 	if err != nil {
-		return fmt.Errorf("getting black: %w", err)
+		return nil, fmt.Errorf("getting black: %w", err)
+	}
+
+	if imgEqual(currentImg, img, epd.Width, epd.Height) {
+		log.Println("Images are equal, doing nothing.")
+		return img, nil
 	}
 
 	defer func() {
@@ -82,15 +87,15 @@ func loop(
 
 	err = initDisplay(display)
 	if err != nil {
-		return fmt.Errorf("initializing display: %w", err)
+		return nil, fmt.Errorf("initializing display: %w", err)
 	}
 
 	display.Clear()
 
-	display.Send(black)
+	display.Send(img)
 	display.Refresh()
 
-	return nil
+	return img, nil
 }
 
 const filename = "/perm/display-epaper-lastFullRefresh"
@@ -131,3 +136,21 @@ func markInitFull() {
 
 	f.Close()
 }
+
+func imgEqual(img1, img2 image.Image, width, height int) bool {
+	if img1 == nil || img2 == nil {
+		return false
+	}
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			r1, g1, b1, a1 := img1.At(x, y).RGBA()
+			r2, g2, b2, a2 := img2.At(x, y).RGBA()
+			if r1 != r2 || g1 != g2 || b1 != b2 || a1 != a2 {
+				return false
+			}
+		}
+	}
+
+	return true
+}