From 98532d8983ffa27ed25449289c98b43d9fd79557 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Thu, 14 Dec 2017 00:25:35 +0900
Subject: [PATCH] graphics: Add TestImageOutside

---
 image.go                    | 11 +++++++++--
 image_test.go               | 39 +++++++++++++++++++++++++++++++++++++
 internal/graphics/shader.go |  3 +++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/image.go b/image.go
index abaa7c0f2..5e44c85c0 100644
--- a/image.go
+++ b/image.go
@@ -98,11 +98,13 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) error {
 	if options == nil {
 		options = &DrawImageOptions{}
 	}
+
 	parts := options.ImageParts
 	// Parts is deprecated. This implementations is for backward compatibility.
 	if parts == nil && options.Parts != nil {
 		parts = imageParts(options.Parts)
 	}
+
 	// ImageParts is deprecated. This implementations is for backward compatibility.
 	if parts != nil {
 		l := parts.Len()
@@ -124,13 +126,18 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) error {
 		}
 		return nil
 	}
+
 	w, h := img.restorable.Size()
 	sx0, sy0, sx1, sy1 := 0, 0, w, h
 	if r := options.SourceRect; r != nil {
 		sx0 = r.Min.X
 		sy0 = r.Min.Y
-		sx1 = r.Max.X
-		sy1 = r.Max.Y
+		if sx1 > r.Max.X {
+			sx1 = r.Max.X
+		}
+		if sy1 > r.Max.Y {
+			sy1 = r.Max.Y
+		}
 	}
 	vs := vertices(sx0, sy0, sx1, sy1, w, h, &options.GeoM.impl)
 	mode := opengl.CompositeMode(options.CompositeMode)
diff --git a/image_test.go b/image_test.go
index 9a0d317e5..9ccc2ae80 100644
--- a/image_test.go
+++ b/image_test.go
@@ -621,3 +621,42 @@ func TestImageLinear(t *testing.T) {
 		}
 	}
 }
+
+func TestImageOutside(t *testing.T) {
+	src, _ := NewImage(5, 10, FilterNearest) // internal texture size is 16x16.
+	dst, _ := NewImage(4, 4, FilterNearest)
+	src.Fill(color.RGBA{0xff, 0, 0, 0xff})
+
+	cases := []struct {
+		X, Y int
+	}{
+		{-4, -4},
+		{5, 0},
+		{0, 10},
+		{5, 10},
+		{16, 0},
+		{0, 16},
+		{16, 16},
+		{16, -4},
+		{-4, 16},
+	}
+	for _, c := range cases {
+		dst.Clear()
+
+		op := &DrawImageOptions{}
+		op.GeoM.Translate(0, 0)
+		r := image.Rect(c.X, c.Y, c.X+4, c.Y+4)
+		op.SourceRect = &r
+		dst.DrawImage(src, op)
+
+		for j := 0; j < 4; j++ {
+			for i := 0; i < 4; i++ {
+				got := color.RGBAModel.Convert(dst.At(i, j)).(color.RGBA)
+				want := color.RGBA{0, 0, 0, 0}
+				if got != want {
+					t.Errorf("src(%d, %d), dst At(%d, %d): got %#v, want: %#v", c.X, c.Y, i, j, got, want)
+				}
+			}
+		}
+	}
+}
diff --git a/internal/graphics/shader.go b/internal/graphics/shader.go
index f98206ada..18cd9a5b6 100644
--- a/internal/graphics/shader.go
+++ b/internal/graphics/shader.go
@@ -83,6 +83,9 @@ highp vec2 roundTexel(highp vec2 p) {
 }
 
 vec4 getColorAt(highp vec2 pos) {
+  if (pos.x < 0.0 || pos.y < 0.0) {
+    return vec4(0, 0, 0, 0);
+  }
   if (pos.x < varying_tex_coord_min.x ||
       pos.y < varying_tex_coord_min.y ||
       varying_tex_coord_max.x <= pos.x ||