From 48a72ca8e36bc87e76f4c4a9b37e438422d26439 Mon Sep 17 00:00:00 2001
From: Ryo Ota <nwtgck@gmail.com>
Date: Wed, 31 Jul 2019 01:52:00 +0900
Subject: [PATCH] [change] Use diff image

---
 gif_progress.go | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/gif_progress.go b/gif_progress.go
index effe5b5..e8d6e1e 100644
--- a/gif_progress.go
+++ b/gif_progress.go
@@ -36,8 +36,9 @@ func AddProgressBar(inOutGif *gif.GIF, barTop bool, barHeight int, barColor colo
 		// Save as previous
 		previousPix = clonePix(newPaletted.Pix)
 
-		// Attach progress bar
+		// Calculate bar width
 		w := int(float32(width) * ((float32(i)+1)/float32(imageLen)))
+		// Attach progress bar
 		for x := 0; x < w; x++ {
 			for h := 0; h < barHeight; h++ {
 				var y = h
@@ -48,7 +49,18 @@ func AddProgressBar(inOutGif *gif.GIF, barTop bool, barHeight int, barColor colo
 			}
 		}
 
+		// Rect of progress bar
+		var barRect image.Rectangle
+		if barTop {
+			barRect = image.Rect(0, 0, w, barHeight)
+		} else  {
+			barRect = image.Rect(0, height - barHeight, w, height)
+		}
+		// Calculate diff image
+		mergedRect := barRect.Union(paletted.Rect)
+		diffImage := newPaletted.SubImage(mergedRect).(*image.Paletted)
+
 		// Update image to new paletted
-		inOutGif.Image[i] = newPaletted
+		inOutGif.Image[i] = diffImage
 	}
 }