From da98e67345a0d86bcf5fa16e5167ee074a9a8ee8 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Tue, 28 Jul 2020 14:02:46 +0900
Subject: [PATCH] mipmap: Bug fix: Wrong level calculation when the indices are
 empty

Fixes #1269
---
 image_test.go             | 11 +++++++++++
 internal/mipmap/mipmap.go |  7 +++++++
 2 files changed, 18 insertions(+)

diff --git a/image_test.go b/image_test.go
index e55fa3869..e5484df1d 100644
--- a/image_test.go
+++ b/image_test.go
@@ -2227,3 +2227,14 @@ func TestImageCompositeModeMultiply(t *testing.T) {
 		}
 	}
 }
+
+// Issue #1269
+func TestImageEmptyTriangle(t *testing.T) {
+	const w, h = 16, 16
+	dst, _ := NewImage(w, h, FilterDefault)
+	src, _ := NewImage(1, 1, FilterDefault)
+
+	vs := []Vertex{}
+	is := []uint16{}
+	dst.DrawTriangles(vs, is, src, nil)
+}
diff --git a/internal/mipmap/mipmap.go b/internal/mipmap/mipmap.go
index 1d8e58b45..c4ffc395c 100644
--- a/internal/mipmap/mipmap.go
+++ b/internal/mipmap/mipmap.go
@@ -91,6 +91,10 @@ func (m *Mipmap) Pixels(x, y, width, height int) ([]byte, error) {
 }
 
 func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageNum]*Mipmap, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, sourceRegion driver.Region, shader *Shader, uniforms []interface{}, canSkipMipmap bool) {
+	if len(indices) == 0 {
+		return
+	}
+
 	level := 0
 	// TODO: Do we need to check all the sources' states of being volatile?
 	if !canSkipMipmap && srcs[0] != nil && !srcs[0].volatile && filter != driver.FilterScreen {
@@ -119,6 +123,9 @@ func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageNum]*Mipmap, vertices [
 				level = l
 			}
 		}
+		if level == math.MaxInt32 {
+			panic("mipmap: level must be calculated at least once but not")
+		}
 	}
 
 	if colorm != nil && colorm.ScaleOnly() {