Add particle blend mode "clip" (#15444)

This lets modders avoid alpha blending rendering bugs as well as potential (future) performance issues.
The appropriate blend modes are also used for node dig particles.

---------

Co-authored-by: sfan5 <sfan5@live.de>

builtin/game/features.lua

@@ -44,6 +44,7 @@ core.features = {
 	bulk_lbms = true,
 	abm_without_neighbors = true,
 	biome_weights = true,
+	particle_blend_clip = true,
 }
 
 function core.has_feature(arg)

doc/breakages.md

@@ -21,3 +21,4 @@ This list is largely advisory and items may be reevaluated once the time comes.
 * merge `sound` and `sounds` table in itemdef
 * remove `DIR_DELIM` from Lua
 * stop reading initial properties from bare entity def
+* change particle default blend mode to `clip`

doc/lua_api.md

@@ -5657,6 +5657,8 @@ Utilities
       abm_without_neighbors = true,
       -- biomes have a weight parameter (5.11.0)
       biome_weights = true,
+      -- Particles can specify a "clip" blend mode (5.11.0)
+      particle_blend_clip = true,
   }
   ```
 
@@ -11483,6 +11485,14 @@ texture = {
     -- (default) blends transparent pixels with those they are drawn atop
     -- according to the alpha channel of the source texture. useful for
     -- e.g. material objects like rocks, dirt, smoke, or node chunks
+    -- note: there will be rendering bugs when particles interact with
+    -- translucent nodes. particles are also not transparency-sorted
+    -- relative to each other.
+    blend = "clip",
+    -- pixels are either fully opaque or fully transparent,
+    -- depending on whether alpha is greater than or less than 50%
+    -- (just like `use_texture_alpha = "clip"` for nodes).
+    -- you should prefer this if you don't need semi-transparency, as it's faster.
     blend = "add",
     -- adds the value of pixels to those underneath them, modulo the sources
     -- alpha channel. useful for e.g. bright light effects like sparks or fire

games/devtest/mods/testtools/particles.lua

@@ -1,14 +1,27 @@
+local function spawn_clip_test_particle(pos)
+	core.add_particle({
+		pos = pos,
+		size = 5,
+		expirationtime = 10,
+		texture = {
+			name = "testtools_particle_clip.png",
+			blend = "clip",
+		},
+	})
+end
+
 core.register_tool("testtools:particle_spawner", {
-	description = "Particle Spawner".."\n"..
+	description = table.concat({
+		"Particle Spawner",
 		"Punch: Spawn random test particle",
+		"Place: Spawn clip test particle",
+	}, "\n"),
 	inventory_image = "testtools_particle_spawner.png",
 	groups = { testtool = 1, disable_repair = 1 },
 	on_use = function(itemstack, user, pointed_thing)
 		local pos = core.get_pointed_thing_position(pointed_thing, true)
 		if pos == nil then
-			if user then
-				pos = user:get_pos()
-			end
+			pos = assert(user):get_pos()
 		end
 		pos = vector.add(pos, {x=0, y=0.5, z=0})
 		local tex, anim
@@ -32,5 +45,12 @@ core.register_tool("testtools:particle_spawner", {
 			glow = math.random(0, 5),
 		})
 	end,
+	on_place = function(itemstack, user, pointed_thing)
+		local pos = assert(core.get_pointed_thing_position(pointed_thing, true))
+		spawn_clip_test_particle(pos)
+	end,
+	on_secondary_use = function(_, user)
+		spawn_clip_test_particle(assert(user):get_pos())
+	end,
 })
 

src/client/particles.cpp

@@ -22,6 +22,8 @@
 #include "settings.h"
 #include "profiler.h"
 
+using BlendMode = ParticleParamTypes::BlendMode;
+
 ClientParticleTexture::ClientParticleTexture(const ServerParticleTexture& p, ITextureSource *tsrc)
 {
 	tex = p;
@@ -603,8 +605,11 @@ video::S3DVertex *ParticleBuffer::getVertices(u16 index)
 
 void ParticleBuffer::OnRegisterSceneNode()
 {
-	if (IsVisible)
-		SceneManager->registerNodeForRendering(this, scene::ESNRP_TRANSPARENT_EFFECT);
+	if (IsVisible) {
+		SceneManager->registerNodeForRendering(this,
+				m_mesh_buffer->getMaterial().MaterialType == video::EMT_TRANSPARENT_ALPHA_CHANNEL_REF
+				? scene::ESNRP_SOLID : scene::ESNRP_TRANSPARENT_EFFECT);
+	}
 	scene::ISceneNode::OnRegisterSceneNode();
 }
 
@@ -906,6 +911,9 @@ void ParticleManager::addNodeParticle(IGameDef *gamedef,
 	if (!getNodeParticleParams(n, f, p, &ref, texpos, texsize, &color))
 		return;
 
+	p.texture.blendmode = f.alpha == ALPHAMODE_BLEND
+			? BlendMode::alpha : BlendMode::clip;
+
 	p.expirationtime = myrand_range(0, 100) / 100.0f;
 
 	// Physics
@@ -940,40 +948,47 @@ void ParticleManager::reserveParticleSpace(size_t max_estimate)
 	m_particles.reserve(m_particles.size() + max_estimate);
 }
 
-video::SMaterial ParticleManager::getMaterialForParticle(const ClientParticleTexRef &texture)
+static void setBlendMode(video::SMaterial &material, BlendMode blendmode)
 {
-	// translate blend modes to GL blend functions
 	video::E_BLEND_FACTOR bfsrc, bfdst;
 	video::E_BLEND_OPERATION blendop;
-	const auto blendmode = texture.tex ? texture.tex->blendmode :
-						   ParticleParamTypes::BlendMode::alpha;
-
 	switch (blendmode) {
-		case ParticleParamTypes::BlendMode::add:
+		case BlendMode::add:
 			bfsrc = video::EBF_SRC_ALPHA;
 			bfdst = video::EBF_DST_ALPHA;
 			blendop = video::EBO_ADD;
 		break;
 
-		case ParticleParamTypes::BlendMode::sub:
+		case BlendMode::sub:
 			bfsrc = video::EBF_SRC_ALPHA;
 			bfdst = video::EBF_DST_ALPHA;
 			blendop = video::EBO_REVSUBTRACT;
 		break;
 
-		case ParticleParamTypes::BlendMode::screen:
+		case BlendMode::screen:
 			bfsrc = video::EBF_ONE;
 			bfdst = video::EBF_ONE_MINUS_SRC_COLOR;
 			blendop = video::EBO_ADD;
 		break;
 
-		default: // includes ParticleParamTypes::BlendMode::alpha
+		default: // includes BlendMode::alpha
 			bfsrc = video::EBF_SRC_ALPHA;
 			bfdst = video::EBF_ONE_MINUS_SRC_ALPHA;
 			blendop = video::EBO_ADD;
 		break;
 	}
 
+	material.MaterialTypeParam = video::pack_textureBlendFunc(
+			bfsrc, bfdst,
+			video::EMFN_MODULATE_1X,
+			video::EAS_TEXTURE | video::EAS_VERTEX_COLOR);
+	material.BlendOperation = blendop;
+}
+
+video::SMaterial ParticleManager::getMaterialForParticle(const Particle *particle)
+{
+	const ClientParticleTexRef &texture = particle->getTextureRef();
+
 	video::SMaterial material;
 
 	// Texture
@@ -984,17 +999,18 @@ video::SMaterial ParticleManager::getMaterialForParticle(const ClientParticleTex
 		tex.MagFilter = video::ETMAGF_NEAREST;
 	});
 
-	// We don't have working transparency sorting. Disable Z-Write for
-	// correct results for clipped-alpha at least.
-	material.ZWriteEnable = video::EZW_OFF;
-
-	// enable alpha blending and set blend mode
-	material.MaterialType = video::EMT_ONETEXTURE_BLEND;
-	material.MaterialTypeParam = video::pack_textureBlendFunc(
-			bfsrc, bfdst,
-			video::EMFN_MODULATE_1X,
-			video::EAS_TEXTURE | video::EAS_VERTEX_COLOR);
-	material.BlendOperation = blendop;
+	const auto blendmode = particle->getBlendMode();
+	if (blendmode == BlendMode::clip) {
+		material.ZWriteEnable = video::EZW_ON;
+		material.MaterialType = video::EMT_TRANSPARENT_ALPHA_CHANNEL_REF;
+		material.MaterialTypeParam = 0.5f;
+	} else {
+		// We don't have working transparency sorting. Disable Z-Write for
+		// correct results for clipped-alpha at least.
+		material.ZWriteEnable = video::EZW_OFF;
+		material.MaterialType = video::EMT_ONETEXTURE_BLEND;
+		setBlendMode(material, blendmode);
+	}
 	material.setTexture(0, texture.ref);
 
 	return material;
@@ -1004,7 +1020,7 @@ bool ParticleManager::addParticle(std::unique_ptr<Particle> toadd)
 {
 	MutexAutoLock lock(m_particle_list_lock);
 
-	auto material = getMaterialForParticle(toadd->getTextureRef());
+	auto material = getMaterialForParticle(toadd.get());
 
 	ParticleBuffer *found = nullptr;
 	// simple shortcut when multiple particles of the same type get added

src/client/particles.h

@@ -77,6 +77,9 @@ public:
 
 	const ClientParticleTexRef &getTextureRef() const { return m_texture; }
 
+	ParticleParamTypes::BlendMode getBlendMode() const
+	{ return m_texture.tex ? m_texture.tex->blendmode : m_p.texture.blendmode; }
+
 	ParticleBuffer *getBuffer() const { return m_buffer; }
 	bool attachToBuffer(ParticleBuffer *buffer);
 
@@ -231,7 +234,7 @@ protected:
 		ParticleParameters &p, video::ITexture **texture, v2f &texpos,
 		v2f &texsize, video::SColor *color, u8 tilenum = 0);
 
-	static video::SMaterial getMaterialForParticle(const ClientParticleTexRef &texture);
+	static video::SMaterial getMaterialForParticle(const Particle *texture);
 
 	bool addParticle(std::unique_ptr<Particle> toadd);
 

src/network/networkprotocol.cpp

@@ -59,9 +59,12 @@
 		Rename TOSERVER_RESPAWN to TOSERVER_RESPAWN_LEGACY
 		Support float animation frame numbers in TOCLIENT_LOCAL_PLAYER_ANIMATIONS
 		[scheduled bump for 5.10.0]
+	PROTOCOL VERSION 47
+		Add particle blend mode "clip"
+		[scheduled bump for 5.11.0]
 */
 
-const u16 LATEST_PROTOCOL_VERSION = 46;
+const u16 LATEST_PROTOCOL_VERSION = 47;
 
 // See also formspec [Version History] in doc/lua_api.md
 const u16 FORMSPEC_API_VERSION = 8;

src/particles.cpp

@@ -190,8 +190,10 @@ void ServerParticleTexture::serialize(std::ostream &os, u16 protocol_ver,
 	FlagT flags = 0;
 	if (animated)
 		flags |= FlagT(ParticleTextureFlags::animated);
-	if (blendmode != BlendMode::alpha)
-		flags |= FlagT(blendmode) << 1;
+	// Default to `blend = "alpha"` for older clients that don't support `blend = "clip"`
+	auto sent_blendmode = (protocol_ver < 47 && blendmode == BlendMode::clip)
+			? BlendMode::alpha : blendmode;
+	flags |= FlagT(sent_blendmode) << 1;
 	serializeParameterValue(os, flags);
 
 	alpha.serialize(os);
@@ -215,6 +217,8 @@ void ServerParticleTexture::deSerialize(std::istream &is, u16 protocol_ver,
 
 	animated = !!(flags & FlagT(ParticleTextureFlags::animated));
 	blendmode = BlendMode((flags & FlagT(ParticleTextureFlags::blend)) >> 1);
+	if (blendmode >= BlendMode::BlendMode_END)
+		throw SerializationError("invalid blend mode");
 
 	alpha.deSerialize(is);
 	scale.deSerialize(is);

src/particles.h

@@ -233,7 +233,8 @@ namespace ParticleParamTypes
 	}
 
 	enum class AttractorKind : u8 { none, point, line, plane };
-	enum class BlendMode     : u8 { alpha, add, sub, screen  };
+	// Note: Allows at most 8 enum members (due to how this is serialized)
+	enum class BlendMode     : u8 { alpha, add, sub, screen, clip, BlendMode_END };
 
 	// these are consistently-named convenience aliases to make code more readable without `using ParticleParamTypes` declarations
 	using v3fRange = RangedParameter<v3fParameter>;

src/script/lua_api/l_particleparams.h

@@ -118,13 +118,14 @@ namespace LuaParticleParams
 			{(int)BlendMode::add,    "add"},
 			{(int)BlendMode::sub,    "sub"},
 			{(int)BlendMode::screen, "screen"},
+			{(int)BlendMode::clip,   "clip"},
 			{0, nullptr},
 		};
 
 		luaL_checktype(L, -1, LUA_TSTRING);
 		int v = (int)BlendMode::alpha;
 		if (!string_to_enum(opts, v, lua_tostring(L, -1))) {
-			throw LuaError("blend mode must be one of ('alpha', 'add', 'sub', 'screen')");
+			throw LuaError("blend mode must be one of ('alpha', 'clip', 'add', 'sub', 'screen')");
 		}
 		ret = (BlendMode)v;
 	}