From afd943c2bf1dd289565be557fa778248fee54247 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 20 Aug 2012 23:27:28 +0300
Subject: [PATCH] Helper functions for post-processors

Most post-processors render fullscreen quads and use a very basic vertex
shader, so it makes sense to provide these as common resources.
---
 source/postprocessor.cpp | 48 ++++++++++++++++++++++++++++++++++++++++
 source/postprocessor.h   | 26 +++++++++++++++++-----
 2 files changed, 69 insertions(+), 5 deletions(-)
 create mode 100644 source/postprocessor.cpp

diff --git a/source/postprocessor.cpp b/source/postprocessor.cpp
new file mode 100644
index 00000000..add8b1ed
--- /dev/null
+++ b/source/postprocessor.cpp
@@ -0,0 +1,48 @@
+#include "mesh.h"
+#include "meshbuilder.h"
+#include "postprocessor.h"
+#include "shader.h"
+
+namespace {
+
+const char fullscreen_vs_source[] =
+	"varying vec2 texcoord;\n"
+	"void main()\n"
+	"{\n"
+	"	gl_Position = gl_Vertex;\n"
+	"	texcoord = gl_Vertex.xy*0.5+0.5;\n"
+	"}\n";
+
+}
+
+
+namespace Msp {
+namespace GL {
+
+Shader &PostProcessor::get_fullscreen_vertex_shader()
+{
+	static Shader shader(VERTEX_SHADER, fullscreen_vs_source);
+	return shader;
+}
+
+const Mesh &PostProcessor::get_fullscreen_quad()
+{
+	static const Mesh &mesh = create_fullscreen_quad();
+	return mesh;
+}
+
+const Mesh &PostProcessor::create_fullscreen_quad()
+{
+	static Mesh mesh(GL::VERTEX2);
+	MeshBuilder builder(mesh);
+	builder.begin(TRIANGLE_STRIP);
+	builder.vertex(-1, 1);
+	builder.vertex(-1, -1);
+	builder.vertex(1, 1);
+	builder.vertex(1, -1);
+	builder.end();
+	return mesh;
+}
+
+} // namespace GL
+} // namespace Msp
diff --git a/source/postprocessor.h b/source/postprocessor.h
index 9e4220ab..d9489de2 100644
--- a/source/postprocessor.h
+++ b/source/postprocessor.h
@@ -4,10 +4,14 @@
 namespace Msp {
 namespace GL {
 
+class Mesh;
+class Shader;
 class Texture2D;
 
 /**
-Base class for post-processing effects.
+Base class for post-processing effects.  Post-processors receive the contents
+of the entire framebuffer as a texture and render it back, altering it in the
+process.
 */
 class PostProcessor
 {
@@ -16,10 +20,22 @@ protected:
 public:
 	virtual ~PostProcessor() { }
 
-	/**
-	Renders the effect.  Takes the source texture as a parameter.
-	*/
-	virtual void render(const Texture2D &, const Texture2D &) = 0;
+	/// Renders the effect.
+	virtual void render(const Texture2D &color, const Texture2D &depth) = 0;
+
+protected:
+	/** Returns a vertex shader suitable for rendering a fullscreen quad.  Input
+	vertices are assumed to be in normalized device coordinates; no transform is
+	done.  The shader provides a varying vec2 texcoord for fragment a shader to
+	access textures. */
+	static Shader &get_fullscreen_vertex_shader();
+
+	/** Returns a mesh consisting of a single quad, covering the entire screen.
+	The vertices are in normalized device coordinates. */
+	static const Mesh &get_fullscreen_quad();
+
+private:
+	static const Mesh &create_fullscreen_quad();
 };
 
 } // namespace GL
-- 
2.43.0