From 06817138c8f234e299a137fab94fb956169d21c5 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 12 Aug 2016 23:39:06 +0300
Subject: [PATCH] Support user clip planes in generated shaders

---
 source/programbuilder.cpp | 21 ++++++++++++++++++---
 source/programbuilder.h   |  6 ++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/source/programbuilder.cpp b/source/programbuilder.cpp
index e1b34d09..f8c3973f 100644
--- a/source/programbuilder.cpp
+++ b/source/programbuilder.cpp
@@ -110,6 +110,7 @@ const ProgramBuilder::VariableDefinition ProgramBuilder::standard_variables[] =
 	{ FRAGMENT, "diffuse_sample", "vec4", "texture2D(diffusemap, texture_coord)", 0 },
 
 	{ VERTEX, "gl_Position", "vec4", "projection_matrix*eye_vertex", 0 },
+	{ VERTEX, "gl_ClipDistance[i]", "float", "dot(eye_vertex, clip_planes[i].equation)", "c" },
 	{ VERTEX, "fog_coord", "float", "-eye_vertex.z", 0 },
 	{ VERTEX, "shd_vertex", "vec3", "(shd_eye_matrix*eye_vertex).xyz", 0 },
 	{ VERTEX, "tbn_sky_dir", "vec3", "eye_sky_dir*eye_tbn_matrix", "n" },
@@ -151,9 +152,11 @@ const ProgramBuilder::VariableDefinition ProgramBuilder::standard_variables[] =
 	{ UNIFORM, "Lighting::fog_color", "vec4", "gl_Fog.color", 0 },
 	{ UNIFORM, "Lighting::fog_density", "float", "gl_Fog.density", 0 },
 	{ UNIFORM, "Material::material", "MaterialParameters", "gl_FrontMaterial", 0 },
+	{ UNIFORM, "Clipping::clip_planes", "ClipPlane[MAX_CLIP_PLANES]", 0, 0 },
 
 	{ TYPE, "LightSourceParameters", "struct { vec4 position; vec4 diffuse; vec4 specular; }", "gl_LightSourceParameters", 0 },
 	{ TYPE, "MaterialParameters", "struct { vec4 ambient; vec4 diffuse; vec4 specular; float shininess; }", "gl_MaterialParameters", 0 },
+	{ TYPE, "ClipPlane", "struct { vec4 equation; }", 0, 0 },
 
 	// Terminator entry
 	{ NO_SCOPE, 0, 0, 0, 0 }
@@ -272,6 +275,8 @@ void ProgramBuilder::add_shaders(Program &prog) const
 	list<ShaderVariable> variables;
 	list<ShaderVariable *> resolved_vars;
 
+	if(features.clipping)
+		variables.push_back(ShaderVariable("gl_ClipDistance[i]"));
 	variables.push_front(ShaderVariable("gl_Position"));
 	variables.push_front(ShaderVariable(features.legacy ? "gl_FragColor" : "frag_color"));
 
@@ -454,6 +459,10 @@ string ProgramBuilder::create_source(const list<ShaderVariable *> &variables, Va
 		}
 	}
 
+	// The clip distance array must be declared manually to give it a size
+	if(scope==VERTEX && features.clipping)
+		source += format("out float gl_ClipDistance[%d];\n", features.max_clip_planes);
+
 	source += "void main()\n{\n";
 
 	list<ShaderVariable *> loop_vars;
@@ -490,7 +499,7 @@ string ProgramBuilder::create_source(const list<ShaderVariable *> &variables, Va
 				}
 
 				InterfaceFlags iface = (*j)->get_interface_flags(scope);
-				if(iface&OUTPUT)
+				if((iface&(OUTPUT|GOAL))==OUTPUT)
 				{
 					string expr = ((*j)->inlined ? create_expression(**j, "i") : (*j)->resolved_name+"[i]");
 					source += format("\t\t%c_%s[i] = %s;\n", interfaces[scope], (*j)->resolved_name, expr);
@@ -503,7 +512,7 @@ string ProgramBuilder::create_source(const list<ShaderVariable *> &variables, Va
 
 		InterfaceFlags iface = (*i)->get_interface_flags(scope);
 
-		if((*i)->array_size>1)
+		if((*i)->array_size>1 || ((*i)->array_size==1 && (iface&GOAL)))
 		{
 			if((*i)->variable->scope==scope || (iface&OUTPUT))
 			{
@@ -731,7 +740,9 @@ ProgramBuilder::StandardFeatures::StandardFeatures():
 	specular(false),
 	normalmap(false),
 	shadow(false),
-	reflection(false)
+	reflection(false),
+	clipping(false),
+	max_clip_planes(1)
 {
 	if(get_gl_api()==OPENGL_ES2)
 		legacy = !(get_glsl_version()>=Version(3, 0));
@@ -762,6 +773,8 @@ string ProgramBuilder::StandardFeatures::create_flags() const
 		flags += 's';
 	if(reflection)
 		flags += 'e';
+	if(clipping)
+		flags += 'c';
 	if(legacy && get_gl_api()==OPENGL)
 		flags += 'g';
 
@@ -861,6 +874,8 @@ void ProgramBuilder::ShaderVariable::resolve_array(const StandardFeatures &featu
 	{
 		if(array_subscript=="MAX_LIGHTS")
 			array_size = features.max_lights;
+		else if(array_subscript=="MAX_CLIP_PLANES")
+			array_size = features.max_clip_planes;
 		else if(isnumrc(array_subscript))
 			array_size = lexical_cast<unsigned>(array_subscript);
 		else
diff --git a/source/programbuilder.h b/source/programbuilder.h
index ecd006d5..97a706e0 100644
--- a/source/programbuilder.h
+++ b/source/programbuilder.h
@@ -98,6 +98,12 @@ public:
 		equivalend in the pipeline. */
 		bool reflection;
 
+		/** Clip primitives against user defined clip planes. */
+		bool clipping;
+
+		/** Number of clipping planes to process. */
+		unsigned max_clip_planes;
+
 		/** Force the use of legacy shaders conforming to GLSL 1.10.   Defaults
 		to true if the version of GLSL is less than 1.30, false otherwise. */
 		bool legacy;
-- 
2.43.0