From 66be53804d352a98e592ddae6704acfe1df23508 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Fri, 2 Jul 2021 22:40:19 +0900
Subject: [PATCH] ebiten: Bug fix: Fill on a sub-image didn't work correctly

Closes #1691
---
 image.go      |  8 +++++++-
 image_test.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/image.go b/image.go
index 04aef49cb..625148315 100644
--- a/image.go
+++ b/image.go
@@ -89,7 +89,13 @@ func init() {
 //
 // When the image is disposed, Fill does nothing.
 func (i *Image) Fill(clr color.Color) {
-	w, h := i.Size()
+	// Use the original size to cover the entire region (#1691).
+	// DrawImage automatically clips the rendering region.
+	orig := i
+	if i.isSubImage() {
+		orig = i.original
+	}
+	w, h := orig.Size()
 
 	op := &DrawImageOptions{}
 	op.GeoM.Scale(float64(w), float64(h))
diff --git a/image_test.go b/image_test.go
index 7ee8c7843..51bd30e56 100644
--- a/image_test.go
+++ b/image_test.go
@@ -2207,3 +2207,36 @@ func TestImageClip(t *testing.T) {
 		}
 	}
 }
+
+// Issue #1691
+func TestImageSubImageFill(t *testing.T) {
+	dst := NewImage(3, 3).SubImage(image.Rect(1, 1, 2, 2)).(*Image)
+	dst.Fill(color.White)
+	for j := 0; j < 3; j++ {
+		for i := 0; i < 3; i++ {
+			got := dst.At(i, j)
+			var want color.RGBA
+			if i == 1 && j == 1 {
+				want = color.RGBA{0xff, 0xff, 0xff, 0xff}
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+
+	dst = NewImage(17, 31).SubImage(image.Rect(3, 4, 8, 10)).(*Image)
+	dst.Fill(color.White)
+	for j := 0; j < 31; j++ {
+		for i := 0; i < 17; i++ {
+			got := dst.At(i, j)
+			var want color.RGBA
+			if 3 <= i && i < 8 && 4 <= j && j < 10 {
+				want = color.RGBA{0xff, 0xff, 0xff, 0xff}
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}