From 631032fefb38f189363c1b81748c44a93167cf7f Mon Sep 17 00:00:00 2001
From: Sorunome <mail@sorunome.de>
Date: Fri, 20 Nov 2020 09:58:23 +0100
Subject: [PATCH] fix: Some gifs not thumbnailing correctly
---
thumbnailing/i/gif.go | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/thumbnailing/i/gif.go b/thumbnailing/i/gif.go
index cae8fc24..f443b13d 100644
--- a/thumbnailing/i/gif.go
+++ b/thumbnailing/i/gif.go
@@ -49,11 +49,13 @@ func (d gifGenerator) GenerateThumbnail(b []byte, contentType string, width int,
disposal = g.Disposal[i]
}
- // if disposal type is 1 (preserve previous frame) we can get artifacts from re-scaling.
- // as such, we re-render those frames to disposal type 0 (start with a transparent frame)
+ // if disposal type is 0 or 1 (preserve previous frame) we can get artifacts from re-scaling.
+ // as such, we re-render those frames to disposal type 1 (do not dispose)
+ // Importantly, we do not clear the previous frame buffer canvas
// see https://www.w3.org/Graphics/GIF/spec-gif89a.txt
- if disposal == 1 {
- g.Disposal[i] = 0
+ // This also applies to frame disposal type 0, https://legacy.imagemagick.org/Usage/anim_basics/#none
+ if disposal == 1 || disposal == 0 {
+ g.Disposal[i] = 1
} else {
draw.Draw(frameImg, frameImg.Bounds(), image.Transparent, image.Point{X: 0, Y: 0}, draw.Src)
}
--
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