From 940d6b11c8065c46d816c607ddb125461205ac7b Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Mon, 3 Oct 2022 01:55:35 +0900
Subject: [PATCH] ebiten: add comments about SubImage as destinations

Updates #2232
---
 image.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/image.go b/image.go
index 5febeeca1..723875410 100644
--- a/image.go
+++ b/image.go
@@ -703,6 +703,10 @@ func (i *Image) DrawRectShader(width, height int, shader *Shader, options *DrawR
 // A sub-image returned by SubImage can be used as a rendering source and a rendering destination.
 // If a sub-image is used as a rendering source, the image is used as if it is a small image.
 // If a sub-image is used as a rendering destination, the region being rendered is clipped.
+//
+// Successive uses of multiple various regions as rendering destination might not be efficient,
+// even though all the underlying images are the same.
+// It's because such renderings cannot be unified into one internal draw command.
 func (i *Image) SubImage(r image.Rectangle) image.Image {
 	i.copyCheck()
 	if i.isDisposed() {