From f298b9541b4a883d57deca601bdca6a2c1b858ba Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Wed, 8 Mar 2023 16:27:36 +0900
Subject: [PATCH] internal/restorable: use a cache for pixels at
 readPixelsFromGPU

Updates #2375
---
 internal/restorable/image.go | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/internal/restorable/image.go b/internal/restorable/image.go
index 5d01b791e..6c03628ca 100644
--- a/internal/restorable/image.go
+++ b/internal/restorable/image.go
@@ -124,12 +124,11 @@ type Image struct {
 	// staleRegions is not used when AlwaysReadPixelsFromGPU() returns true.
 	staleRegions []image.Rectangle
 
-	// pixelsForRestore is cached byte slices for pixels.
-	// pixelsForRestore is just a cache to avoid allocations (#2375).
-	// pixelsForRestore is used only at restore.
+	// pixelsCache is cached byte slices for pixels.
+	// pixelsCache is just a cache to avoid allocations (#2375).
 	//
 	// A key is the region and a value is a byte slice for the region.
-	pixelsForRestore map[image.Rectangle][]byte
+	pixelsCache map[image.Rectangle][]byte
 
 	// regionsForRestore is cached regions.
 	// regionsForRestore is just a cache to avoid allocations (#2375).
@@ -485,7 +484,15 @@ func (i *Image) readPixelsFromGPU(graphicsDriver graphicsdriver.Graphics) error
 			continue
 		}
 
-		pix := make([]byte, 4*r.Dx()*r.Dy())
+		if i.pixelsCache == nil {
+			i.pixelsCache = map[image.Rectangle][]byte{}
+		}
+
+		pix, ok := i.pixelsCache[r]
+		if !ok {
+			pix = make([]byte, 4*r.Dx()*r.Dy())
+			i.pixelsCache[r] = pix
+		}
 		if err := i.image.ReadPixels(graphicsDriver, pix, r.Min.X, r.Min.Y, r.Dx(), r.Dy()); err != nil {
 			return err
 		}
@@ -612,14 +619,14 @@ func (i *Image) restore(graphicsDriver graphicsdriver.Graphics) error {
 				continue
 			}
 
-			if i.pixelsForRestore == nil {
-				i.pixelsForRestore = map[image.Rectangle][]byte{}
+			if i.pixelsCache == nil {
+				i.pixelsCache = map[image.Rectangle][]byte{}
 			}
 
-			pix, ok := i.pixelsForRestore[r]
+			pix, ok := i.pixelsCache[r]
 			if !ok {
 				pix = make([]byte, 4*r.Dx()*r.Dy())
-				i.pixelsForRestore[r] = pix
+				i.pixelsCache[r] = pix
 			}
 			if err := gimg.ReadPixels(graphicsDriver, pix, r.Min.X, r.Min.Y, r.Dx(), r.Dy()); err != nil {
 				return err
@@ -645,7 +652,7 @@ func (i *Image) Dispose() {
 	i.image.Dispose()
 	i.image = nil
 	i.basePixels = Pixels{}
-	i.pixelsForRestore = nil
+	i.pixelsCache = nil
 	i.clearDrawTrianglesHistory()
 	i.stale = false
 	i.staleRegions = i.staleRegions[:0]