From b48d501bc07727a6119d3608eee06a296769c581 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Fri, 23 Nov 2018 19:01:16 +0900
Subject: [PATCH] graphics: Explicit limitation of indices at DrawTriangles

Fixes #728
---
 image.go                            | 8 ++++++++
 internal/graphicscommand/command.go | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/image.go b/image.go
index 413261a0e..96299edb8 100644
--- a/image.go
+++ b/image.go
@@ -440,10 +440,15 @@ type DrawTrianglesOptions struct {
 	Filter Filter
 }
 
+// MaxIndicesNum is the maximum number of indices for DrawTriangles.
+const MaxIndicesNum = graphics.IndicesNum
+
 // DrawTriangles draws a triangle with the specified vertices and their indices.
 //
 // If len(indices) is not multiple of 3, DrawTriangles panics.
 //
+// If len(indices) is more than MaxIndicesNum, DrawTriangles panics.
+//
 // The rule in which DrawTriangles works effectively is same as DrawImage's.
 //
 // In contrast to DrawImage, DrawTriangles doesn't care source image edges.
@@ -473,6 +478,9 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 	if len(indices)%3 != 0 {
 		panic("ebiten: len(indices) % 3 must be 0")
 	}
+	if len(indices) > MaxIndicesNum {
+		panic("ebiten: len(indices) must be <= MaxIndicesNum")
+	}
 	// TODO: Check the maximum value of indices and len(vertices)?
 
 	if options == nil {
diff --git a/internal/graphicscommand/command.go b/internal/graphicscommand/command.go
index 903e6f3f9..1321ecc4a 100644
--- a/internal/graphicscommand/command.go
+++ b/internal/graphicscommand/command.go
@@ -89,7 +89,7 @@ func (q *commandQueue) appendIndices(indices []uint16, offset uint16) {
 
 func (q *commandQueue) doEnqueueDrawImageCommand(dst, src *Image, nvertices, nindices int, color *affine.ColorM, mode graphics.CompositeMode, filter graphics.Filter, forceNewCommand bool) {
 	if nindices > graphics.IndicesNum {
-		panic("not implemented for too many indices")
+		panic("not reached")
 	}
 	if !forceNewCommand && 0 < len(q.commands) {
 		if last := q.commands[len(q.commands)-1]; last.CanMerge(dst, src, color, mode, filter) {