From e7556941c41b1a0fc84fe7986c98ee79eccbf564 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 9 Sep 2013 19:00:40 +0300
Subject: [PATCH] Add a flag to RenderPass to render the back faces of a mesh

This is useful for transparency effects.
---
 source/renderer.cpp    | 12 +++++++++++-
 source/renderer.h      |  1 +
 source/renderpass.cpp  |  8 ++++++--
 source/renderpass.h    |  3 +++
 source/windingtest.cpp | 14 ++++++++++++--
 source/windingtest.h   |  6 ++++--
 6 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/source/renderer.cpp b/source/renderer.cpp
index 3a44dcd3..31d9621e 100644
--- a/source/renderer.cpp
+++ b/source/renderer.cpp
@@ -112,6 +112,11 @@ void Renderer::set_winding_test(const WindingTest *w)
 	state->winding_test = w;
 }
 
+void Renderer::set_reverse_winding(bool r)
+{
+	state->reverse_winding = r;
+}
+
 void Renderer::push_state()
 {
 	state_stack.push_back(state_stack.back());
@@ -220,7 +225,12 @@ void Renderer::apply_state()
 		Program::unbind();
 
 	if(state->winding_test)
-		state->winding_test->bind();
+	{
+		if(state->reverse_winding)
+			state->winding_test->get_reverse().bind();
+		else
+			state->winding_test->bind();
+	}
 	else
 		WindingTest::unbind();
 
diff --git a/source/renderer.h b/source/renderer.h
index 00f97004..1254b7ad 100644
--- a/source/renderer.h
+++ b/source/renderer.h
@@ -125,6 +125,7 @@ public:
 	void set_vertex_array(const VertexArray *);
 	void set_element_buffer(const Buffer *);
 	void set_winding_test(const WindingTest *);
+	void set_reverse_winding(bool);
 
 	/** Saves the current state so it can be restored later. */
 	void push_state();
diff --git a/source/renderpass.cpp b/source/renderpass.cpp
index 9ee79d4b..158e9fc8 100644
--- a/source/renderpass.cpp
+++ b/source/renderpass.cpp
@@ -20,7 +20,8 @@ RenderPass::RenderPass():
 	shprog(0),
 	shdata(0),
 	material(0),
-	texturing(0)
+	texturing(0),
+	back_faces(false)
 { }
 
 RenderPass::RenderPass(const RenderPass &other):
@@ -28,7 +29,8 @@ RenderPass::RenderPass(const RenderPass &other):
 	shdata(other.shdata ? new ProgramData(*other.shdata) : 0),
 	material(other.material),
 	texturing(other.texturing ? new Texturing(*other.texturing) : 0),
-	tex_names(other.tex_names)
+	tex_names(other.tex_names),
+	back_faces(other.back_faces)
 { }
 
 RenderPass::~RenderPass()
@@ -70,6 +72,7 @@ void RenderPass::apply(Renderer &renderer) const
 	renderer.set_texturing(texturing);
 	renderer.set_material(material.get());
 	renderer.set_shader_program(shprog, shdata.get());
+	renderer.set_reverse_winding(back_faces);
 }
 
 
@@ -90,6 +93,7 @@ void RenderPass::Loader::init()
 	add("shader",   &RenderPass::shprog);
 	add("material", &Loader::material_inline);
 	add("material", &Loader::material);
+	add("back_faces",&RenderPass::back_faces);
 	add("texunit",  &Loader::texunit);
 	add("texunit",  &Loader::texunit_named);
 	add("uniforms", &Loader::uniforms);
diff --git a/source/renderpass.h b/source/renderpass.h
index e891802e..934a213e 100644
--- a/source/renderpass.h
+++ b/source/renderpass.h
@@ -63,6 +63,7 @@ private:
 	RefPtr<const Material> material;
 	Texturing *texturing;
 	std::map<std::string, unsigned> tex_names;
+	bool back_faces;
 
 	RenderPass &operator=(const RenderPass &);
 public:
@@ -78,6 +79,8 @@ public:
 	void set_texture(unsigned, const Texture *);
 	const Texturing *get_texturing() const { return texturing; }
 	int get_texture_index(const std::string &) const;
+	void set_back_faces(bool);
+	bool get_back_faces() const { return back_faces; }
 
 	void apply(Renderer &) const;
 };
diff --git a/source/windingtest.cpp b/source/windingtest.cpp
index de9e0a25..acbc20fc 100644
--- a/source/windingtest.cpp
+++ b/source/windingtest.cpp
@@ -44,13 +44,23 @@ void WindingTest::unbind()
 		glDisable(GL_CULL_FACE);
 }
 
-WindingTest &WindingTest::clockwise()
+const WindingTest &WindingTest::get_reverse() const
+{
+	if(!test)
+		return *this;
+	else if(winding==CLOCKWISE)
+		return counterclockwise();
+	else
+		return clockwise();
+}
+
+const WindingTest &WindingTest::clockwise()
 {
 	static WindingTest test(CLOCKWISE);
 	return test;
 }
 
-WindingTest &WindingTest::counterclockwise()
+const WindingTest &WindingTest::counterclockwise()
 {
 	static WindingTest test(COUNTERCLOCKWISE);
 	return test;
diff --git a/source/windingtest.h b/source/windingtest.h
index 0869d565..d8a4c421 100644
--- a/source/windingtest.h
+++ b/source/windingtest.h
@@ -34,8 +34,10 @@ public:
 
 	static void unbind();
 
-	static WindingTest &clockwise();
-	static WindingTest &counterclockwise();
+	const WindingTest &get_reverse() const;
+
+	static const WindingTest &clockwise();
+	static const WindingTest &counterclockwise();
 };
 
 } // namespace GL
-- 
2.43.0