From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 11 Mar 2022 09:55:49 +0000 (+0200)
Subject: Implement alpha cutoff for materials
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=ae423e6ef278388f92802fbae34b1c7ec339292f

Implement alpha cutoff for materials

Having to implement it separately in each material's shader is not
optimal, but since they each define their own uniform block, no better
solution is readily apparent.

The occluder shader also supports alpha cutoff so that objects with
such materials can cast proper shadows.
---

diff --git a/shaderlib/cooktorrance.glsl b/shaderlib/cooktorrance.glsl
index ff1a56c7..ad1a459d 100644
--- a/shaderlib/cooktorrance.glsl
+++ b/shaderlib/cooktorrance.glsl
@@ -13,6 +13,7 @@ struct PbrMaterialParameters
 uniform PbrMaterial
 {
 	PbrMaterialParameters pbr_material;
+	float alpha_cutoff;
 };
 
 uniform sampler2D base_color_map;
@@ -29,6 +30,7 @@ layout(constant_id=auto) const bool use_occlusion_map = false;
 layout(constant_id=auto) const bool use_emission = false;
 layout(constant_id=auto) const bool use_emission_map = false;
 layout(constant_id=auto) const bool use_image_based_lighting = false;
+layout(constant_id=auto) const bool use_alpha_cutoff = false;
 
 #pragma MSP stage(fragment)
 virtual vec4 get_base_color()
@@ -173,10 +175,13 @@ vec3 cooktorrance_lighting(vec3 normal, vec3 look, vec3 base_color, float metaln
 
 void main()
 {
+	vec4 base_color = get_base_color();
+	if(use_alpha_cutoff && base_color.a<alpha_cutoff)
+		discard;
+
 	vec3 normal = get_fragment_normal();
 	vec3 look = normalize(world_look_dir);
 
-	vec4 base_color = get_base_color();
 	float metalness = get_metalness_value();
 	float roughness = get_roughness_value();
 
diff --git a/shaderlib/occluder.glsl b/shaderlib/occluder.glsl
index b5d05f09..abd29a0a 100644
--- a/shaderlib/occluder.glsl
+++ b/shaderlib/occluder.glsl
@@ -1,5 +1,14 @@
 import msp_interface;
 
+uniform AlphaCutoff
+{
+	float alpha_cutoff;
+};
+
+uniform sampler2D alpha_map;
+
+layout(constant_id=auto) const bool use_alpha_cutoff = false;
+
 #pragma MSP stage(vertex)
 virtual vec4 get_vertex_position()
 {
@@ -20,4 +29,19 @@ void main()
 	vec4 eye_vertex = eye_world_matrix*get_vertex_transform()*get_vertex_position();
 	clipping(eye_vertex.xyz);
 	gl_Position = clip_eye_matrix*eye_vertex;
+	passthrough;
+}
+
+#pragma MSP stage(fragment)
+layout(location=0) out vec4 frag_color;
+
+void main()
+{
+	if(use_alpha_cutoff)
+	{
+		float alpha = texture(alpha_map, texcoord.xy).a;
+		if(alpha<alpha_cutoff)
+			discard;
+		frag_color = vec4(1.0);
+	}
 }
diff --git a/shaderlib/phong.glsl b/shaderlib/phong.glsl
index 080c9048..23489711 100644
--- a/shaderlib/phong.glsl
+++ b/shaderlib/phong.glsl
@@ -14,6 +14,7 @@ struct BasicMaterialParameters
 uniform BasicMaterial
 {
 	BasicMaterialParameters basic_material;
+	float alpha_cutoff;
 };
 
 uniform sampler2D diffuse_map;
@@ -30,6 +31,7 @@ layout(constant_id=auto) const bool use_emission = false;
 layout(constant_id=auto) const bool use_emission_map = false;
 layout(constant_id=auto) const bool use_reflectivity = false;
 layout(constant_id=auto) const bool use_reflectivity_map = false;
+layout(constant_id=auto) const bool use_alpha_cutoff = false;
 
 #pragma MSP stage(fragment)
 virtual vec4 get_diffuse_color()
@@ -112,10 +114,13 @@ vec3 phong_lighting(vec3 normal, vec3 look, vec3 surface_diffuse, vec3 surface_s
 
 void main()
 {
+	vec4 surface_diffuse = get_diffuse_color();
+	if(use_alpha_cutoff && surface_diffuse.a<alpha_cutoff)
+		discard;
+
 	vec3 normal = get_fragment_normal();
 	vec3 look = normalize(world_look_dir);
 
-	vec4 surface_diffuse = get_diffuse_color();
 	vec3 surface_specular = get_specular_color();
 	float shininess = get_shininess_value();
 
diff --git a/shaderlib/unlit.glsl b/shaderlib/unlit.glsl
index 85275558..f4920a79 100644
--- a/shaderlib/unlit.glsl
+++ b/shaderlib/unlit.glsl
@@ -9,6 +9,7 @@ struct UnlitMaterialParameters
 uniform UnlitMaterial
 {
 	UnlitMaterialParameters unlit_material;
+	float alpha_cutoff;
 };
 
 uniform sampler2D color_tex;
@@ -16,6 +17,7 @@ uniform sampler2D color_tex;
 layout(constant_id=auto) const bool use_texture = false;
 layout(constant_id=auto) const bool use_vertex_color = false;
 layout(constant_id=auto) const bool use_fog = false;
+layout(constant_id=auto) const bool use_alpha_cutoff = false;
 
 #pragma MSP stage(fragment)
 virtual vec4 get_color()
@@ -31,6 +33,9 @@ virtual vec4 get_color()
 void main()
 {
 	vec4 color = get_color();
+	if(use_alpha_cutoff && color.a<alpha_cutoff)
+		discard;
+
 	if(use_fog)
 		color.rgb = apply_fog(color.rgb);
 	frag_color = color;
diff --git a/source/materials/material.cpp b/source/materials/material.cpp
index a34c0457..6af833e6 100644
--- a/source/materials/material.cpp
+++ b/source/materials/material.cpp
@@ -11,10 +11,18 @@ using namespace std;
 namespace Msp {
 namespace GL {
 
+Material::Material()
+{
+	set_alpha_cutoff(0.0f);
+}
+
 const Program *Material::create_compatible_shader(const map<string, int> &extra_spec) const
 {
 	string module_name;
 	map<string, int> spec_values;
+	if(alpha_cutoff>0.0f)
+		spec_values["use_alpha_cutoff"] = true;
+
 	fill_program_info(module_name, spec_values);
 
 	for(const auto &kvp: extra_spec)
@@ -48,6 +56,12 @@ const Program *Material::create_compatible_shader(const map<string, int> &extra_
 	return shprog;
 }
 
+void Material::set_alpha_cutoff(float a)
+{
+	alpha_cutoff = a;
+	shdata.uniform("alpha_cutoff", a);
+}
+
 void Material::set_debug_name(const string &name)
 {
 #ifdef DEBUG
@@ -78,9 +92,15 @@ Material::Loader::Loader(Material &m, Collection &c):
 
 void Material::Loader::init_actions()
 {
+	add("alpha_cutoff", &Loader::alpha_cutoff);
 	add("sampler", &Loader::sampler);
 }
 
+void Material::Loader::alpha_cutoff(float a)
+{
+	obj.set_alpha_cutoff(a);
+}
+
 void Material::Loader::sampler(const string &name)
 {
 	obj.sampler = &get_collection().get<Sampler>(name);
diff --git a/source/materials/material.h b/source/materials/material.h
index ff7f53c0..75ff972c 100644
--- a/source/materials/material.h
+++ b/source/materials/material.h
@@ -27,6 +27,7 @@ private:
 		virtual void init_actions();
 
 	private:
+		void alpha_cutoff(float);
 		void sampler(const std::string &);
 	};
 
@@ -72,9 +73,10 @@ public:
 
 protected:
 	const Sampler *sampler = 0;
+	float alpha_cutoff = 0.0f;
 	ProgramData shdata;
 
-	Material() = default;
+	Material();
 public:
 	virtual ~Material() = default;
 
@@ -96,6 +98,9 @@ public:
 	virtual const Texture *get_texture(Tag) const = 0;
 	virtual const Sampler *get_sampler(Tag) const { return sampler; }
 
+	void set_alpha_cutoff(float a);
+	float get_alpha_cutoff() const { return alpha_cutoff; }
+
 	void set_debug_name(const std::string &);
 
 	template<typename T>