Added premult alpha blending to 3D (spatial) shaders.

Co-authored-by: jitspoe <jitspoe@yahoo.com>
Co-authored-by: Clay John <claynjohn@gmail.com>

doc/classes/BaseMaterial3D.xml

@@ -609,6 +609,9 @@
 		<constant name="BLEND_MODE_MUL" value="3" enum="BlendMode">
 			The color of the object is multiplied by the background.
 		</constant>
+		<constant name="BLEND_MODE_PREMULT_ALPHA" value="4" enum="BlendMode">
+			The color of the object is added to the background and the alpha channel is used to mask out the background. This is effectively a hybrid of the blend mix and add modes, useful for FX like fire where you want the flame to add but the smoke to mix. By default, this works with unshaded materials using premultiplied textures. For shaded materials, use the PREMUL_ALPHA_FACTOR built-in so that lighting can be modulated as well.
+		</constant>
 		<constant name="ALPHA_ANTIALIASING_OFF" value="0" enum="AlphaAntiAliasing">
 			Disables Alpha AntiAliasing for the material.
 		</constant>

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -3040,6 +3040,11 @@ void RasterizerSceneGLES3::_render_list_template(RenderListParameters *p_params,
 								glBlendFuncSeparate(GL_DST_COLOR, GL_ZERO, GL_ZERO, GL_ONE);
 							}
 
+						} break;
+						case GLES3::SceneShaderData::BLEND_MODE_PREMULT_ALPHA: {
+							glBlendEquation(GL_FUNC_ADD);
+							glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
+
 						} break;
 						case GLES3::SceneShaderData::BLEND_MODE_ALPHA_TO_COVERAGE: {
 							// Do nothing for now.

drivers/gles3/shaders/scene.glsl

@@ -1442,6 +1442,9 @@ void main() {
 	float clearcoat_roughness = 0.0;
 	float anisotropy = 0.0;
 	vec2 anisotropy_flow = vec2(1.0, 0.0);
+#ifdef PREMULT_ALPHA_USED
+	float premult_alpha = 1.0;
+#endif
 #ifndef FOG_DISABLED
 	vec4 fog = vec4(0.0);
 #endif // !FOG_DISABLED
@@ -2141,9 +2144,12 @@ void main() {
 
 	frag_color.rgb += additive_light_color;
 #endif // USE_ADDITIVE_LIGHTING
-
 	frag_color.rgb *= scene_data.luminance_multiplier;
 
 #endif // !RENDER_MATERIAL
 #endif // !MODE_RENDER_DEPTH
+
+#ifdef PREMULT_ALPHA_USED
+	frag_color.rgb *= premult_alpha;
+#endif
 }

drivers/gles3/storage/material_storage.cpp

@@ -1243,6 +1243,7 @@ MaterialStorage::MaterialStorage() {
 		actions.renames["NORMAL_MAP_DEPTH"] = "normal_map_depth";
 		actions.renames["ALBEDO"] = "albedo";
 		actions.renames["ALPHA"] = "alpha";
+		actions.renames["PREMULT_ALPHA_FACTOR"] = "premult_alpha";
 		actions.renames["METALLIC"] = "metallic";
 		actions.renames["SPECULAR"] = "specular";
 		actions.renames["ROUGHNESS"] = "roughness";
@@ -1327,6 +1328,7 @@ MaterialStorage::MaterialStorage() {
 		actions.usage_defines["ALPHA_HASH_SCALE"] = "#define ALPHA_HASH_USED\n";
 		actions.usage_defines["ALPHA_ANTIALIASING_EDGE"] = "#define ALPHA_ANTIALIASING_EDGE_USED\n";
 		actions.usage_defines["ALPHA_TEXTURE_COORDINATE"] = "@ALPHA_ANTIALIASING_EDGE";
+		actions.usage_defines["PREMULT_ALPHA_FACTOR"] = "#define PREMULT_ALPHA_USED";
 
 		actions.usage_defines["SSS_STRENGTH"] = "#define ENABLE_SSS\n";
 		actions.usage_defines["SSS_TRANSMITTANCE_DEPTH"] = "#define ENABLE_TRANSMITTANCE\n";
@@ -2908,6 +2910,7 @@ void SceneShaderData::set_code(const String &p_code) {
 	actions.render_mode_values["blend_mix"] = Pair<int *, int>(&blend_modei, BLEND_MODE_MIX);
 	actions.render_mode_values["blend_sub"] = Pair<int *, int>(&blend_modei, BLEND_MODE_SUB);
 	actions.render_mode_values["blend_mul"] = Pair<int *, int>(&blend_modei, BLEND_MODE_MUL);
+	actions.render_mode_values["blend_premult_alpha"] = Pair<int *, int>(&blend_modei, BLEND_MODE_PREMULT_ALPHA);
 
 	actions.render_mode_values["alpha_to_coverage"] = Pair<int *, int>(&alpha_antialiasing_modei, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE);
 	actions.render_mode_values["alpha_to_coverage_and_one"] = Pair<int *, int>(&alpha_antialiasing_modei, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE_AND_TO_ONE);

drivers/gles3/storage/material_storage.h

@@ -248,6 +248,7 @@ struct SceneShaderData : public ShaderData {
 		BLEND_MODE_ADD,
 		BLEND_MODE_SUB,
 		BLEND_MODE_MUL,
+		BLEND_MODE_PREMULT_ALPHA,
 		BLEND_MODE_ALPHA_TO_COVERAGE
 	};
 

scene/resources/material.cpp

@@ -688,6 +688,9 @@ void BaseMaterial3D::_update_shader() {
 		case BLEND_MODE_MUL:
 			code += "blend_mul";
 			break;
+		case BLEND_MODE_PREMULT_ALPHA:
+			code += "blend_premul_alpha";
+			break;
 		case BLEND_MODE_MAX:
 			break; // Internal value, skip.
 	}
@@ -1819,6 +1822,11 @@ void fragment() {)";
 	vec3 detail = mix(ALBEDO.rgb, ALBEDO.rgb * detail_tex.rgb, detail_tex.a);
 )";
 			} break;
+			case BLEND_MODE_PREMULT_ALPHA: {
+				// This is unlikely to ever be used for detail textures, and in order for it to function in the editor, another bit must be used in MaterialKey,
+				// but there are only 5 bits left, so I'm going to leave this disabled unless it's actually requested.
+				//code += "\tvec3 detail = (1.0-detail_tex.a)*ALBEDO.rgb+detail_tex.rgb;\n";
+			} break;
 			case BLEND_MODE_MAX:
 				break; // Internal value, skip.
 		}
@@ -3040,7 +3048,7 @@ void BaseMaterial3D::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "alpha_hash_scale", PROPERTY_HINT_RANGE, "0,2,0.01"), "set_alpha_hash_scale", "get_alpha_hash_scale");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "alpha_antialiasing_mode", PROPERTY_HINT_ENUM, "Disabled,Alpha Edge Blend,Alpha Edge Clip"), "set_alpha_antialiasing", "get_alpha_antialiasing");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "alpha_antialiasing_edge", PROPERTY_HINT_RANGE, "0,1,0.01"), "set_alpha_antialiasing_edge", "get_alpha_antialiasing_edge");
-	ADD_PROPERTY(PropertyInfo(Variant::INT, "blend_mode", PROPERTY_HINT_ENUM, "Mix,Add,Subtract,Multiply"), "set_blend_mode", "get_blend_mode");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "blend_mode", PROPERTY_HINT_ENUM, "Mix,Add,Subtract,Multiply,Premultiplied Alpha"), "set_blend_mode", "get_blend_mode");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "cull_mode", PROPERTY_HINT_ENUM, "Back,Front,Disabled"), "set_cull_mode", "get_cull_mode");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "depth_draw_mode", PROPERTY_HINT_ENUM, "Opaque Only,Always,Never"), "set_depth_draw_mode", "get_depth_draw_mode");
 	ADD_PROPERTYI(PropertyInfo(Variant::BOOL, "no_depth_test"), "set_flag", "get_flag", FLAG_DISABLE_DEPTH_TEST);
@@ -3269,6 +3277,7 @@ void BaseMaterial3D::_bind_methods() {
 	BIND_ENUM_CONSTANT(BLEND_MODE_ADD);
 	BIND_ENUM_CONSTANT(BLEND_MODE_SUB);
 	BIND_ENUM_CONSTANT(BLEND_MODE_MUL);
+	BIND_ENUM_CONSTANT(BLEND_MODE_PREMULT_ALPHA);
 
 	BIND_ENUM_CONSTANT(ALPHA_ANTIALIASING_OFF);
 	BIND_ENUM_CONSTANT(ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE);

scene/resources/material.h

@@ -219,6 +219,7 @@ class BaseMaterial3D : public Material {
 		BLEND_MODE_ADD,
 		BLEND_MODE_SUB,
 		BLEND_MODE_MUL,
+		BLEND_MODE_PREMULT_ALPHA,
 		BLEND_MODE_MAX
 	};
 

servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp

@@ -90,6 +90,7 @@ void SceneShaderForwardClustered::ShaderData::set_code(const String &p_code) {
 	actions.render_mode_values["blend_mix"] = Pair<int *, int>(&blend_mode, BLEND_MODE_MIX);
 	actions.render_mode_values["blend_sub"] = Pair<int *, int>(&blend_mode, BLEND_MODE_SUB);
 	actions.render_mode_values["blend_mul"] = Pair<int *, int>(&blend_mode, BLEND_MODE_MUL);
+	actions.render_mode_values["blend_premult_alpha"] = Pair<int *, int>(&blend_mode, BLEND_MODE_PREMULT_ALPHA);
 
 	actions.render_mode_values["alpha_to_coverage"] = Pair<int *, int>(&alpha_antialiasing_mode, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE);
 	actions.render_mode_values["alpha_to_coverage_and_one"] = Pair<int *, int>(&alpha_antialiasing_mode, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE_AND_TO_ONE);
@@ -244,7 +245,17 @@ void SceneShaderForwardClustered::ShaderData::set_code(const String &p_code) {
 			blend_attachment.dst_color_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
 			blend_attachment.src_alpha_blend_factor = RD::BLEND_FACTOR_ONE;
 			blend_attachment.dst_alpha_blend_factor = RD::BLEND_FACTOR_ZERO;
-		}
+		} break;
+		case BLEND_MODE_PREMULT_ALPHA: {
+			blend_attachment.enable_blend = true;
+			blend_attachment.alpha_blend_op = RD::BLEND_OP_ADD;
+			blend_attachment.color_blend_op = RD::BLEND_OP_ADD;
+			blend_attachment.src_color_blend_factor = RD::BLEND_FACTOR_ONE;
+			blend_attachment.dst_color_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
+			blend_attachment.src_alpha_blend_factor = RD::BLEND_FACTOR_ONE;
+			blend_attachment.dst_alpha_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
+			uses_blend_alpha = true; // Force alpha used because of blend.
+		} break;
 	}
 
 	// Color pass -> attachment 0: Color/Diffuse, attachment 1: Separate Specular, attachment 2: Motion Vectors
@@ -593,6 +604,7 @@ void SceneShaderForwardClustered::init(const String p_defines) {
 		actions.renames["NORMAL_MAP_DEPTH"] = "normal_map_depth";
 		actions.renames["ALBEDO"] = "albedo";
 		actions.renames["ALPHA"] = "alpha";
+		actions.renames["PREMULT_ALPHA_FACTOR"] = "premult_alpha";
 		actions.renames["METALLIC"] = "metallic";
 		actions.renames["SPECULAR"] = "specular";
 		actions.renames["ROUGHNESS"] = "roughness";
@@ -672,6 +684,7 @@ void SceneShaderForwardClustered::init(const String p_defines) {
 		actions.usage_defines["INSTANCE_CUSTOM"] = "#define ENABLE_INSTANCE_CUSTOM\n";
 		actions.usage_defines["POSITION"] = "#define OVERRIDE_POSITION\n";
 		actions.usage_defines["LIGHT_VERTEX"] = "#define LIGHT_VERTEX_USED\n";
+		actions.usage_defines["PREMULT_ALPHA_FACTOR"] = "#define PREMULT_ALPHA_USED\n";
 
 		actions.usage_defines["ALPHA_SCISSOR_THRESHOLD"] = "#define ALPHA_SCISSOR_USED\n";
 		actions.usage_defines["ALPHA_HASH_SCALE"] = "#define ALPHA_HASH_USED\n";

servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.h

@@ -106,7 +106,8 @@ class SceneShaderForwardClustered {
 			BLEND_MODE_ADD,
 			BLEND_MODE_SUB,
 			BLEND_MODE_MUL,
-			BLEND_MODE_ALPHA_TO_COVERAGE
+			BLEND_MODE_ALPHA_TO_COVERAGE,
+			BLEND_MODE_PREMULT_ALPHA,
 		};
 
 		enum DepthDraw {

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.cpp

@@ -91,6 +91,7 @@ void SceneShaderForwardMobile::ShaderData::set_code(const String &p_code) {
 	actions.render_mode_values["blend_mix"] = Pair<int *, int>(&blend_mode, BLEND_MODE_MIX);
 	actions.render_mode_values["blend_sub"] = Pair<int *, int>(&blend_mode, BLEND_MODE_SUB);
 	actions.render_mode_values["blend_mul"] = Pair<int *, int>(&blend_mode, BLEND_MODE_MUL);
+	actions.render_mode_values["blend_premult_alpha"] = Pair<int *, int>(&blend_mode, BLEND_MODE_PREMULT_ALPHA);
 
 	actions.render_mode_values["alpha_to_coverage"] = Pair<int *, int>(&alpha_antialiasing_mode, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE);
 	actions.render_mode_values["alpha_to_coverage_and_one"] = Pair<int *, int>(&alpha_antialiasing_mode, ALPHA_ANTIALIASING_ALPHA_TO_COVERAGE_AND_TO_ONE);
@@ -255,7 +256,17 @@ void SceneShaderForwardMobile::ShaderData::set_code(const String &p_code) {
 			blend_attachment.dst_color_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
 			blend_attachment.src_alpha_blend_factor = RD::BLEND_FACTOR_ONE;
 			blend_attachment.dst_alpha_blend_factor = RD::BLEND_FACTOR_ZERO;
-		}
+		} break;
+		case BLEND_MODE_PREMULT_ALPHA: {
+			blend_attachment.enable_blend = true;
+			blend_attachment.alpha_blend_op = RD::BLEND_OP_ADD;
+			blend_attachment.color_blend_op = RD::BLEND_OP_ADD;
+			blend_attachment.src_color_blend_factor = RD::BLEND_FACTOR_ONE;
+			blend_attachment.dst_color_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
+			blend_attachment.src_alpha_blend_factor = RD::BLEND_FACTOR_ONE;
+			blend_attachment.dst_alpha_blend_factor = RD::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
+			uses_blend_alpha = true; // Force alpha used because of blend.
+		} break;
 	}
 
 	RD::PipelineColorBlendState blend_state_blend;
@@ -497,6 +508,7 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 		actions.renames["NORMAL_MAP_DEPTH"] = "normal_map_depth";
 		actions.renames["ALBEDO"] = "albedo";
 		actions.renames["ALPHA"] = "alpha";
+		actions.renames["PREMULT_ALPHA_FACTOR"] = "premult_alpha";
 		actions.renames["METALLIC"] = "metallic";
 		actions.renames["SPECULAR"] = "specular";
 		actions.renames["ROUGHNESS"] = "roughness";
@@ -581,6 +593,7 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 		actions.usage_defines["ALPHA_HASH_SCALE"] = "#define ALPHA_HASH_USED\n";
 		actions.usage_defines["ALPHA_ANTIALIASING_EDGE"] = "#define ALPHA_ANTIALIASING_EDGE_USED\n";
 		actions.usage_defines["ALPHA_TEXTURE_COORDINATE"] = "@ALPHA_ANTIALIASING_EDGE";
+		actions.usage_defines["PREMULT_ALPHA_FACTOR"] = "#define PREMULT_ALPHA_USED";
 
 		actions.usage_defines["SSS_STRENGTH"] = "#define ENABLE_SSS\n";
 		actions.usage_defines["SSS_TRANSMITTANCE_DEPTH"] = "#define ENABLE_TRANSMITTANCE\n";

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.h

@@ -61,6 +61,7 @@ class SceneShaderForwardMobile {
 			BLEND_MODE_ADD,
 			BLEND_MODE_SUB,
 			BLEND_MODE_MUL,
+			BLEND_MODE_PREMULT_ALPHA,
 			BLEND_MODE_ALPHA_TO_COVERAGE
 		};
 

servers/rendering/renderer_rd/shaders/forward_clustered/scene_forward_clustered.glsl

@@ -914,6 +914,9 @@ vec3 encode24(vec3 v) {
 void fragment_shader(in SceneData scene_data) {
 	uint instance_index = instance_index_interp;
 
+#ifdef PREMULT_ALPHA_USED
+	float premult_alpha = 1.0;
+#endif // PREMULT_ALPHA_USED
 	//lay out everything, whatever is unused is optimized away anyway
 	vec3 vertex = vertex_interp;
 #ifdef USE_MULTIVIEW
@@ -2458,6 +2461,10 @@ void fragment_shader(in SceneData scene_data) {
 
 	motion_vector = prev_position_uv - position_uv;
 #endif
+
+#if defined(PREMULT_ALPHA_USED) && !defined(MODE_RENDER_DEPTH)
+	frag_color.rgb *= premult_alpha;
+#endif //PREMULT_ALPHA_USED
 }
 
 void main() {

servers/rendering/renderer_rd/shaders/forward_mobile/scene_forward_mobile.glsl

@@ -749,6 +749,9 @@ void main() {
 	float clearcoat_roughness = 0.0;
 	float anisotropy = 0.0;
 	vec2 anisotropy_flow = vec2(1.0, 0.0);
+#ifdef PREMULT_ALPHA_USED
+	float premult_alpha = 1.0;
+#endif
 #ifndef FOG_DISABLED
 	vec4 fog = vec4(0.0);
 #endif // !FOG_DISABLED
@@ -1846,6 +1849,9 @@ void main() {
 	// On mobile we use a UNORM buffer with 10bpp which results in a range from 0.0 - 1.0 resulting in HDR breaking
 	// We divide by sc_luminance_multiplier to support a range from 0.0 - 2.0 both increasing precision on bright and darker images
 	frag_color.rgb = frag_color.rgb / sc_luminance_multiplier;
+#ifdef PREMULT_ALPHA_USED
+	frag_color.rgb *= premult_alpha;
+#endif
 
 #endif //MODE_MULTIPLE_RENDER_TARGETS
 

servers/rendering/shader_types.cpp

@@ -124,6 +124,7 @@ ShaderTypes::ShaderTypes() {
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["UV2"] = constt(ShaderLanguage::TYPE_VEC2);
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["COLOR"] = constt(ShaderLanguage::TYPE_VEC4);
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["ALBEDO"] = ShaderLanguage::TYPE_VEC3;
+	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["PREMULT_ALPHA_FACTOR"] = ShaderLanguage::TYPE_FLOAT;
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["ALPHA"] = ShaderLanguage::TYPE_FLOAT;
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["METALLIC"] = ShaderLanguage::TYPE_FLOAT;
 	shader_modes[RS::SHADER_SPATIAL].functions["fragment"].built_ins["SPECULAR"] = ShaderLanguage::TYPE_FLOAT;
@@ -208,7 +209,7 @@ ShaderTypes::ShaderTypes() {
 
 	// spatial render modes
 	{
-		shader_modes[RS::SHADER_SPATIAL].modes.push_back({ PNAME("blend"), "mix", "add", "sub", "mul" });
+		shader_modes[RS::SHADER_SPATIAL].modes.push_back({ PNAME("blend"), "mix", "add", "sub", "mul", "premult_alpha" });
 		shader_modes[RS::SHADER_SPATIAL].modes.push_back({ PNAME("depth_draw"), "opaque", "always", "never" });
 		shader_modes[RS::SHADER_SPATIAL].modes.push_back({ PNAME("depth_prepass_alpha") });
 		shader_modes[RS::SHADER_SPATIAL].modes.push_back({ PNAME("depth_test_disabled") });