From b856ccc893a102536048e8d67a6577a31ebdf166 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 25 May 2020 18:17:28 +0300
Subject: [PATCH] Change Texturing to store index-texture pairs

Modern GPUs have a large number of texture binding points so storing
texture pointers for all of them is inefficient.
---
 source/texturing.cpp | 90 ++++++++++++++++++++++++++++++--------------
 source/texturing.h   | 16 ++++----
 2 files changed, 71 insertions(+), 35 deletions(-)

diff --git a/source/texturing.cpp b/source/texturing.cpp
index dff3757f..d8d178b3 100644
--- a/source/texturing.cpp
+++ b/source/texturing.cpp
@@ -23,36 +23,46 @@ void Texturing::detach(unsigned attch)
 	set_attachment(attch, 0);
 }
 
-void Texturing::set_attachment(unsigned attch, const Texture *tex)
+void Texturing::set_attachment(unsigned unit, const Texture *tex)
 {
-	if(attch>=TexUnit::get_n_units())
+	if(unit>=TexUnit::get_n_units())
 		throw out_of_range("Texturing::set_attachment");
 
-	if(attachments.size()<=attch)
-		attachments.resize(attch+1);
-
-	attachments[attch] = tex;
-
-	if(current()==this)
-		bind_attachment(attch);
-}
-
-const Texture *Texturing::get_attached_texture(unsigned i) const
-{
-	return i<attachments.size() ? attachments[i] : 0;
-}
+	if(tex)
+	{
+		vector<Attachment>::iterator i;
+		for(i=attachments.begin(); (i!=attachments.end() && i->unit<=unit); ++i)
+			if(i->unit==unit)
+			{
+				i->texture = tex;
+				if(current()==this)
+					tex->bind_to(unit);
+				return;
+			}
 
-void Texturing::bind_attachment(unsigned i) const
-{
-	if(const Texture *tex = attachments[i])
-		tex->bind_to(i);
+		attachments.insert(i, Attachment(unit, tex));
+		if(current()==this)
+			tex->bind_to(unit);
+	}
 	else
-		Texture::unbind_from(i);
+	{
+		for(vector<Attachment>::iterator i=attachments.begin(); (i!=attachments.end() && i->unit<=unit); ++i)
+			if(i->unit==unit)
+			{
+				attachments.erase(i);
+				if(current()==this)
+					Texture::unbind_from(unit);
+				return;
+			}
+	}
 }
 
-void Texturing::unbind_attachment(unsigned i)
+const Texture *Texturing::get_attached_texture(unsigned unit) const
 {
-	Texture::unbind_from(i);
+	for(vector<Attachment>::const_iterator i=attachments.begin(); (i!=attachments.end() && i->unit<=unit); ++i)
+		if(i->unit==unit)
+			return i->texture;
+	return 0;
 }
 
 void Texturing::bind() const
@@ -60,12 +70,30 @@ void Texturing::bind() const
 	const Texturing *old = current();
 	if(set_current(this))
 	{
-		for(unsigned i=0; i<attachments.size(); ++i)
-			bind_attachment(i);
 		if(old)
 		{
-			for(unsigned i=attachments.size(); i<old->attachments.size(); ++i)
-				unbind_attachment(i);
+			vector<Attachment>::const_iterator i = attachments.begin();
+			vector<Attachment>::const_iterator j = old->attachments.begin();
+			while(i!=attachments.end() || j!=old->attachments.end())
+			{
+				if(i!=attachments.end() && (j==old->attachments.end() || i->unit<=j->unit))
+				{
+					i->texture->bind_to(i->unit);
+					if(j!=old->attachments.end() && j->unit==i->unit)
+						++j;
+					++i;
+				}
+				else
+				{
+					Texture::unbind_from(j->unit);
+					++j;
+				}
+			}
+		}
+		else
+		{
+			for(vector<Attachment>::const_iterator i=attachments.begin(); i!=attachments.end(); ++i)
+				i->texture->bind_to(i->unit);
 		}
 	}
 }
@@ -75,10 +103,16 @@ void Texturing::unbind()
 	const Texturing *old = current();
 	if(set_current(0))
 	{
-		for(unsigned i=old->attachments.size(); i--;)
-			unbind_attachment(i);
+		for(vector<Attachment>::const_iterator i=old->attachments.begin(); i!=old->attachments.end(); ++i)
+			Texture::unbind_from(i->unit);
 	}
 }
 
+
+Texturing::Attachment::Attachment(unsigned u, const Texture *t):
+	unit(u),
+	texture(t)
+{ }
+
 } // namespace GL
 } // namespace Msp;
diff --git a/source/texturing.h b/source/texturing.h
index 0b3a9751..79647f1d 100644
--- a/source/texturing.h
+++ b/source/texturing.h
@@ -12,7 +12,15 @@ class Texture;
 class Texturing: public Bindable<Texturing>
 {
 private:
-	std::vector<const Texture *> attachments;
+	struct Attachment
+	{
+		unsigned unit;
+		const Texture *texture;
+
+		Attachment(unsigned, const Texture *);
+	};
+
+	std::vector<Attachment> attachments;
 
 public:
 	~Texturing();
@@ -24,12 +32,6 @@ private:
 public:
 	const Texture *get_attached_texture(unsigned) const;
 
-private:
-	void bind_attachment(unsigned) const;
-
-	static void unbind_attachment(unsigned);
-
-public:
 	void bind() const;
 
 	static void unbind();
-- 
2.45.2