From 974a7ab596ba0ef6776c4c34a04ad66a8c5e70d9 Mon Sep 17 00:00:00 2001
From: ernestrc <ernest@unstable.build>
Date: Sun, 23 Jun 2024 23:52:08 -0700
Subject: [PATCH] Update image.DrawTriangles to re-use indices

Reduces allocations and GC overhead for programs that
call this method hundreds of times per rendered frame.
---
 image.go | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/image.go b/image.go
index 58ee22640..7f51a3e34 100644
--- a/image.go
+++ b/image.go
@@ -43,6 +43,9 @@ type Image struct {
 	// tmpVertices must not be reused until ui.Image.Draw* is called.
 	tmpVertices []float32
 
+	// tmpIndices must not be reused until ui.Image.Draw* is called.
+	tmpIndices []uint32
+
 	// tmpUniforms must not be reused until ui.Image.Draw* is called.
 	tmpUniforms []uint32
 
@@ -514,7 +517,7 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 			vs[i*graphics.VertexFloatCount+7] = v.ColorA * ca
 		}
 	}
-	is := make([]uint32, len(indices))
+	is := i.ensureTmpIndices(len(indices))
 	for i := range is {
 		is[i] = uint32(indices[i])
 	}
@@ -664,7 +667,7 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 		vs[i*graphics.VertexFloatCount+7] = v.ColorA
 	}
 
-	is := make([]uint32, len(indices))
+	is := i.ensureTmpIndices(len(indices))
 	for i := range is {
 		is[i] = uint32(indices[i])
 	}
@@ -1265,6 +1268,13 @@ func (i *Image) ensureTmpVertices(n int) []float32 {
 	return i.tmpVertices[:n]
 }
 
+func (i *Image) ensureTmpIndices(n int) []uint32 {
+	if cap(i.tmpIndices) < n {
+		i.tmpIndices = make([]uint32, n)
+	}
+	return i.tmpIndices[:n]
+}
+
 // private implements FinalScreen.
 func (*Image) private() {
 }