From e7d080ca4a3a77410c226d9c3b63af3df461f68b Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Wed, 21 Oct 2020 11:28:01 +0900
Subject: [PATCH] mipmap: Bug fix: Too big scale tried to allocate too big
 images

Fixes #1399
---
 examples/camera/main.go   |  4 ++--
 image_test.go             | 11 +++++++++++
 internal/mipmap/mipmap.go | 23 ++++++++++++++++-------
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/examples/camera/main.go b/examples/camera/main.go
index 2399c1ccc..aa6a26214 100644
--- a/examples/camera/main.go
+++ b/examples/camera/main.go
@@ -148,12 +148,12 @@ func (g *Game) Update() error {
 	}
 
 	if ebiten.IsKeyPressed(ebiten.KeyQ) {
-		if g.camera.ZoomFactor > -240 {
+		if g.camera.ZoomFactor > -2400 {
 			g.camera.ZoomFactor -= 1
 		}
 	}
 	if ebiten.IsKeyPressed(ebiten.KeyE) {
-		if g.camera.ZoomFactor < 240 {
+		if g.camera.ZoomFactor < 2400 {
 			g.camera.ZoomFactor += 1
 		}
 	}
diff --git a/image_test.go b/image_test.go
index 237cf6874..90dca2d38 100644
--- a/image_test.go
+++ b/image_test.go
@@ -2149,3 +2149,14 @@ func TestImageDrawImageTooSmallScale(t *testing.T) {
 	op.GeoM.Scale(1e-10, 1e-10)
 	dst.DrawImage(src, op)
 }
+
+// Issue #1399
+func TestImageDrawImageCannotCreateMiamap(t *testing.T) {
+	dst := NewImage(1, 1)
+	src := NewImage(4096, 4096)
+
+	op := &DrawImageOptions{}
+	op.GeoM.Scale(64, 64)
+	dst.DrawImage(src, op)
+	dst.At(0, 0)
+}
diff --git a/internal/mipmap/mipmap.go b/internal/mipmap/mipmap.go
index 9165f200f..056812727 100644
--- a/internal/mipmap/mipmap.go
+++ b/internal/mipmap/mipmap.go
@@ -230,6 +230,13 @@ func (m *Mipmap) level(level int) *buffered.Image {
 		m.imgs[level] = nil
 		return nil
 	}
+	// buffered.NewImage panics with a too big size when actual allocation happens.
+	// 4096 should be a safe size in most environments (#1399).
+	// Unfortunately a precise max image size cannot be obtained here since this requires GPU access.
+	if w2 > 4096 || h2 > 4096 {
+		m.imgs[level] = nil
+		return nil
+	}
 	s := buffered.NewImage(w2, h2)
 	s.SetVolatile(m.volatile)
 	s.DrawTriangles([graphics.ShaderImageNum]*buffered.Image{src}, vs, is, nil, driver.CompositeModeCopy, filter, driver.AddressUnsafe, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
@@ -262,7 +269,9 @@ func (m *Mipmap) MarkDisposed() {
 
 func (m *Mipmap) disposeMipmaps() {
 	for _, img := range m.imgs {
-		img.MarkDisposed()
+		if img != nil {
+			img.MarkDisposed()
+		}
 	}
 	for k := range m.imgs {
 		delete(m.imgs, k)
@@ -271,7 +280,7 @@ func (m *Mipmap) disposeMipmaps() {
 
 // mipmapLevel returns an appropriate mipmap level for the given distance.
 func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, filter driver.Filter) int {
-	const maxScale = 6
+	const maxLevel = 6
 
 	if filter == driver.FilterScreen {
 		return 0
@@ -287,7 +296,7 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 	// Scale can be infinite when the specified scale is extremely big (#1398).
 	if math.IsInf(float64(scale), 0) {
 		if filter == driver.FilterNearest {
-			return -maxScale
+			return -maxLevel
 		}
 		return 0
 	}
@@ -327,8 +336,8 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 
 		// If tooBigScale is 32, level -6 means that the maximum scale is 32 * 2^6 = 2048. This should be
 		// enough.
-		if level < -maxScale {
-			level = -maxScale
+		if level < -maxLevel {
+			level = -maxLevel
 		}
 		return level
 	}
@@ -361,8 +370,8 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 		}
 	}
 
-	if level > maxScale {
-		level = maxScale
+	if level > maxLevel {
+		level = maxLevel
 	}
 
 	return level