From 40f728a3263c33e4fe9ba0681711a38799621405 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Tue, 12 Feb 2019 16:13:33 +0900
Subject: [PATCH] shareable: Call (*restorable.Image).Clear() when possible

This is a kind of relanding of c68c36b0b70e77af1d7892eb8e2d89fa13526112.
Clearing the restorable.Image state can reduce the operations for
restoring.
---
 internal/restorable/image.go    | 5 +++++
 internal/shareable/shareable.go | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/internal/restorable/image.go b/internal/restorable/image.go
index 68544de26..1fd0b4612 100644
--- a/internal/restorable/image.go
+++ b/internal/restorable/image.go
@@ -103,6 +103,11 @@ func NewScreenFramebufferImage(width, height int) *Image {
 	return i
 }
 
+func (i *Image) Clear() {
+	theImages.makeStaleIfDependingOn(i)
+	i.clear()
+}
+
 func (i *Image) clear() {
 	if i.priority {
 		panic("restorable: clear cannot be called on a priority image")
diff --git a/internal/shareable/shareable.go b/internal/shareable/shareable.go
index 6bc3207fa..92442c1a3 100644
--- a/internal/shareable/shareable.go
+++ b/internal/shareable/shareable.go
@@ -278,6 +278,11 @@ func (i *Image) Fill(r, g, b, a uint8) {
 	i.ensureNotShared()
 	backendsM.Unlock()
 
+	if r == 0 && g == 0 && b == 0 && a == 0 {
+		i.backend.restorable.Clear()
+		return
+	}
+
 	rf := float32(0)
 	gf := float32(0)
 	bf := float32(0)