From b4f45edff8644df3402bf4f6c7860929c9fbcd29 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sat, 30 Oct 2021 00:13:57 +0900
Subject: [PATCH] internal/graphicsdriver/opengl: Optimization: Avoid creating
 slices for every frame

---
 internal/graphicsdriver/opengl/graphics.go |  9 +++++++++
 internal/graphicsdriver/opengl/program.go  | 16 +++++++---------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/internal/graphicsdriver/opengl/graphics.go b/internal/graphicsdriver/opengl/graphics.go
index 960241b8a..a10ae3e19 100644
--- a/internal/graphicsdriver/opengl/graphics.go
+++ b/internal/graphicsdriver/opengl/graphics.go
@@ -28,6 +28,11 @@ func Get() *Graphics {
 	return &theGraphics
 }
 
+type activatedTexture struct {
+	textureNative textureNative
+	index         int
+}
+
 type Graphics struct {
 	state   openGLState
 	context context
@@ -42,6 +47,10 @@ type Graphics struct {
 	drawCalled bool
 
 	uniformVariableNameCache map[int]string
+
+	// activatedTextures is a set of activated textures.
+	// textureNative cannot be a map key unfortunately.
+	activatedTextures []activatedTexture
 }
 
 func (g *Graphics) Begin() {
diff --git a/internal/graphicsdriver/opengl/program.go b/internal/graphicsdriver/opengl/program.go
index 94135e28e..05b452055 100644
--- a/internal/graphicsdriver/opengl/program.go
+++ b/internal/graphicsdriver/opengl/program.go
@@ -297,13 +297,6 @@ func (g *Graphics) useProgram(program program, uniforms []uniformVariable, textu
 		}
 	}
 
-	type activatedTexture struct {
-		textureNative textureNative
-		index         int
-	}
-
-	// textureNative cannot be a map key unfortunately.
-	textureToActivatedTexture := []activatedTexture{}
 	var idx int
 loop:
 	for i, t := range textures {
@@ -313,14 +306,14 @@ loop:
 
 		// If the texture is already bound, set the texture variable to point to the texture.
 		// Rebinding the same texture seems problematic (#1193).
-		for _, at := range textureToActivatedTexture {
+		for _, at := range g.activatedTextures {
 			if t.native.equal(at.textureNative) {
 				g.context.uniformInt(program, fmt.Sprintf("T%d", i), at.index)
 				continue loop
 			}
 		}
 
-		textureToActivatedTexture = append(textureToActivatedTexture, activatedTexture{
+		g.activatedTextures = append(g.activatedTextures, activatedTexture{
 			textureNative: t.native,
 			index:         idx,
 		})
@@ -336,5 +329,10 @@ loop:
 		idx++
 	}
 
+	for i := range g.activatedTextures {
+		g.activatedTextures[i] = activatedTexture{}
+	}
+	g.activatedTextures = g.activatedTextures[:0]
+
 	return nil
 }