Rework use_texture_alpha to provide three opaque/clip/blend modes

The change that turns nodeboxes and meshes opaque when possible is kept,
as is the compatibility code that warns modders to adjust their nodedefs.

builtin/game/features.lua

@@ -18,6 +18,7 @@ core.features = {
 	pathfinder_works = true,
 	object_step_has_moveresult = true,
 	direct_velocity_on_players = true,
+	use_texture_alpha_string_modes = true,
 }
 
 function core.has_feature(arg)

doc/lua_api.txt

@@ -4386,6 +4386,8 @@ Utilities
           object_step_has_moveresult = true,
           -- Whether get_velocity() and add_velocity() can be used on players (5.4.0)
           direct_velocity_on_players = true,
+          -- nodedef's use_texture_alpha accepts new string modes (5.4.0)
+          use_texture_alpha_string_modes = true,
       }
 
 * `minetest.has_feature(arg)`: returns `boolean, missing_features`
@@ -7340,10 +7342,18 @@ Used by `minetest.register_node`.
         -- If the node has a palette, then this setting only has an effect in
         -- the inventory and on the wield item.
 
-        use_texture_alpha = false,
-        -- Use texture's alpha channel
-        -- If this is set to false, the node will be rendered fully opaque
-        -- regardless of any texture transparency.
+        use_texture_alpha = ...,
+        -- Specifies how the texture's alpha channel will be used for rendering.
+        -- possible values:
+        -- * "opaque": Node is rendered opaque regardless of alpha channel
+        -- * "clip": A given pixel is either fully see-through or opaque
+        --           depending on the alpha channel being below/above 50% in value
+        -- * "blend": The alpha channel specifies how transparent a given pixel
+        --            of the rendered node is
+        -- The default is "opaque" for drawtypes normal, liquid and flowingliquid;
+        -- "clip" otherwise.
+        -- If set to a boolean value (deprecated): true either sets it to blend
+        -- or clip, false sets it to clip or opaque mode depending on the drawtype.
 
         palette = "palette.png",
         -- The node's `param2` is used to select a pixel from the image.

src/nodedef.cpp

@@ -360,7 +360,7 @@ void ContentFeatures::reset()
 		i = TileDef();
 	for (auto &j : tiledef_special)
 		j = TileDef();
-	alpha = 255;
+	alpha = ALPHAMODE_OPAQUE;
 	post_effect_color = video::SColor(0, 0, 0, 0);
 	param_type = CPT_NONE;
 	param_type_2 = CPT2_NONE;
@@ -405,6 +405,31 @@ void ContentFeatures::reset()
 	node_dig_prediction = "air";
 }
 
+void ContentFeatures::setAlphaFromLegacy(u8 legacy_alpha)
+{
+	// No special handling for nodebox/mesh here as it doesn't make sense to
+	// throw warnings when the server is too old to support the "correct" way
+	switch (drawtype) {
+	case NDT_NORMAL:
+		alpha = legacy_alpha == 255 ? ALPHAMODE_OPAQUE : ALPHAMODE_CLIP;
+		break;
+	case NDT_LIQUID:
+	case NDT_FLOWINGLIQUID:
+		alpha = legacy_alpha == 255 ? ALPHAMODE_OPAQUE : ALPHAMODE_BLEND;
+		break;
+	default:
+		alpha = legacy_alpha == 255 ? ALPHAMODE_CLIP : ALPHAMODE_BLEND;
+		break;
+	}
+}
+
+u8 ContentFeatures::getAlphaForLegacy() const
+{
+	// This is so simple only because 255 and 0 mean wildly different things
+	// depending on drawtype...
+	return alpha == ALPHAMODE_OPAQUE ? 255 : 0;
+}
+
 void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 {
 	const u8 version = CONTENTFEATURES_VERSION;
@@ -433,7 +458,7 @@ void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 	for (const TileDef &td : tiledef_special) {
 		td.serialize(os, protocol_version);
 	}
-	writeU8(os, alpha);
+	writeU8(os, getAlphaForLegacy());
 	writeU8(os, color.getRed());
 	writeU8(os, color.getGreen());
 	writeU8(os, color.getBlue());
@@ -489,6 +514,7 @@ void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 
 	os << serializeString16(node_dig_prediction);
 	writeU8(os, leveled_max);
+	writeU8(os, alpha);
 }
 
 void ContentFeatures::deSerialize(std::istream &is)
@@ -524,7 +550,7 @@ void ContentFeatures::deSerialize(std::istream &is)
 		throw SerializationError("unsupported CF_SPECIAL_COUNT");
 	for (TileDef &td : tiledef_special)
 		td.deSerialize(is, version, drawtype);
-	alpha = readU8(is);
+	setAlphaFromLegacy(readU8(is));
 	color.setRed(readU8(is));
 	color.setGreen(readU8(is));
 	color.setBlue(readU8(is));
@@ -582,10 +608,16 @@ void ContentFeatures::deSerialize(std::istream &is)
 
 	try {
 		node_dig_prediction = deSerializeString16(is);
-		u8 tmp_leveled_max = readU8(is);
+
+		u8 tmp = readU8(is);
 		if (is.eof()) /* readU8 doesn't throw exceptions so we have to do this */
 			throw SerializationError("");
-		leveled_max = tmp_leveled_max;
+		leveled_max = tmp;
+
+		tmp = readU8(is);
+		if (is.eof())
+			throw SerializationError("");
+		alpha = static_cast<enum AlphaMode>(tmp);
 	} catch(SerializationError &e) {};
 }
 
@@ -677,6 +709,7 @@ bool ContentFeatures::textureAlphaCheck(ITextureSource *tsrc, const TileDef *til
 	video::IVideoDriver *driver = RenderingEngine::get_video_driver();
 	static thread_local bool long_warning_printed = false;
 	std::set<std::string> seen;
+
 	for (int i = 0; i < length; i++) {
 		if (seen.find(tiles[i].name) != seen.end())
 			continue;
@@ -701,20 +734,21 @@ bool ContentFeatures::textureAlphaCheck(ITextureSource *tsrc, const TileDef *til
 
 break_loop:
 		image->drop();
-		if (!ok) {
-			warningstream << "Texture \"" << tiles[i].name << "\" of "
-				<< name << " has transparent pixels, assuming "
-				"use_texture_alpha = true." << std::endl;
-			if (!long_warning_printed) {
-				warningstream << "  This warning can be a false-positive if "
-					"unused pixels in the texture are transparent. However if "
-					"it is meant to be transparent, you *MUST* update the "
-					"nodedef and set use_texture_alpha = true! This compatibility "
-					"code will be removed in a few releases." << std::endl;
-				long_warning_printed = true;
-			}
-			return true;
+		if (ok)
+			continue;
+		warningstream << "Texture \"" << tiles[i].name << "\" of "
+			<< name << " has transparency, assuming "
+			"use_texture_alpha = \"clip\"." << std::endl;
+		if (!long_warning_printed) {
+			warningstream << "  This warning can be a false-positive if "
+				"unused pixels in the texture are transparent. However if "
+				"it is meant to be transparent, you *MUST* update the "
+				"nodedef and set use_texture_alpha = \"clip\"! This "
+				"compatibility code will be removed in a few releases."
+				<< std::endl;
+			long_warning_printed = true;
 		}
+		return true;
 	}
 	return false;
 }
@@ -759,29 +793,33 @@ void ContentFeatures::updateTextures(ITextureSource *tsrc, IShaderSource *shdsrc
 
 	bool is_liquid = false;
 
-	MaterialType material_type = (alpha == 255) ?
-		TILE_MATERIAL_BASIC : TILE_MATERIAL_ALPHA;
+	if (alpha == ALPHAMODE_LEGACY_COMPAT) {
+		// Before working with the alpha mode, resolve any legacy kludges
+		alpha = textureAlphaCheck(tsrc, tdef, 6) ? ALPHAMODE_CLIP : ALPHAMODE_OPAQUE;
+	}
+
+	MaterialType material_type = alpha == ALPHAMODE_OPAQUE ?
+		TILE_MATERIAL_OPAQUE : (alpha == ALPHAMODE_CLIP ? TILE_MATERIAL_BASIC :
+		TILE_MATERIAL_ALPHA);
 
 	switch (drawtype) {
 	default:
 	case NDT_NORMAL:
-		material_type = (alpha == 255) ?
-			TILE_MATERIAL_OPAQUE : TILE_MATERIAL_ALPHA;
 		solidness = 2;
 		break;
 	case NDT_AIRLIKE:
 		solidness = 0;
 		break;
 	case NDT_LIQUID:
 		if (tsettings.opaque_water)
-			alpha = 255;
+			alpha = ALPHAMODE_OPAQUE;
 		solidness = 1;
 		is_liquid = true;
 		break;
 	case NDT_FLOWINGLIQUID:
 		solidness = 0;
 		if (tsettings.opaque_water)
-			alpha = 255;
+			alpha = ALPHAMODE_OPAQUE;
 		is_liquid = true;
 		break;
 	case NDT_GLASSLIKE:
@@ -833,19 +871,16 @@ void ContentFeatures::updateTextures(ITextureSource *tsrc, IShaderSource *shdsrc
 		break;
 	case NDT_MESH:
 	case NDT_NODEBOX:
-		if (alpha == 255 && textureAlphaCheck(tsrc, tdef, 6))
-			alpha = 0;
-
 		solidness = 0;
-		if (waving == 1)
+		if (waving == 1) {
 			material_type = TILE_MATERIAL_WAVING_PLANTS;
-		else if (waving == 2)
+		} else if (waving == 2) {
 			material_type = TILE_MATERIAL_WAVING_LEAVES;
-		else if (waving == 3)
-			material_type = (alpha == 255) ? TILE_MATERIAL_WAVING_LIQUID_OPAQUE :
-				TILE_MATERIAL_WAVING_LIQUID_BASIC;
-		else if (alpha == 255)
-			material_type = TILE_MATERIAL_OPAQUE;
+		} else if (waving == 3) {
+			material_type = alpha == ALPHAMODE_OPAQUE ?
+				TILE_MATERIAL_WAVING_LIQUID_OPAQUE : (alpha == ALPHAMODE_CLIP ?
+				TILE_MATERIAL_WAVING_LIQUID_BASIC : TILE_MATERIAL_WAVING_LIQUID_TRANSPARENT);
+		}
 		break;
 	case NDT_TORCHLIKE:
 	case NDT_SIGNLIKE:
@@ -860,10 +895,11 @@ void ContentFeatures::updateTextures(ITextureSource *tsrc, IShaderSource *shdsrc
 
 	if (is_liquid) {
 		if (waving == 3) {
-			material_type = (alpha == 255) ? TILE_MATERIAL_WAVING_LIQUID_OPAQUE :
-				TILE_MATERIAL_WAVING_LIQUID_TRANSPARENT;
+			material_type = alpha == ALPHAMODE_OPAQUE ?
+				TILE_MATERIAL_WAVING_LIQUID_OPAQUE : (alpha == ALPHAMODE_CLIP ?
+				TILE_MATERIAL_WAVING_LIQUID_BASIC : TILE_MATERIAL_WAVING_LIQUID_TRANSPARENT);
 		} else {
-			material_type = (alpha == 255) ? TILE_MATERIAL_LIQUID_OPAQUE :
+			material_type = alpha == ALPHAMODE_OPAQUE ? TILE_MATERIAL_LIQUID_OPAQUE :
 				TILE_MATERIAL_LIQUID_TRANSPARENT;
 		}
 	}

src/nodedef.h

@@ -231,6 +231,14 @@ enum AlignStyle : u8 {
 	ALIGN_STYLE_USER_DEFINED,
 };
 
+enum AlphaMode : u8 {
+	ALPHAMODE_BLEND,
+	ALPHAMODE_CLIP,
+	ALPHAMODE_OPAQUE,
+	ALPHAMODE_LEGACY_COMPAT, /* means either opaque or clip */
+};
+
+
 /*
 	Stand-alone definition of a TileSpec (basically a server-side TileSpec)
 */
@@ -315,9 +323,7 @@ struct ContentFeatures
 	// These will be drawn over the base tiles.
 	TileDef tiledef_overlay[6];
 	TileDef tiledef_special[CF_SPECIAL_COUNT]; // eg. flowing liquid
-	// If 255, the node is opaque.
-	// Otherwise it uses texture alpha.
-	u8 alpha;
+	AlphaMode alpha;
 	// The color of the node.
 	video::SColor color;
 	std::string palette_name;
@@ -418,20 +424,27 @@ struct ContentFeatures
 	void serialize(std::ostream &os, u16 protocol_version) const;
 	void deSerialize(std::istream &is);
 
-#ifndef SERVER
-	/*
-	 * Checks if any tile texture has any transparent pixels.
-	 * Prints a warning and returns true if that is the case, false otherwise.
-	 * This is supposed to be used for use_texture_alpha backwards compatibility.
-	 */
-	bool textureAlphaCheck(ITextureSource *tsrc, const TileDef *tiles,
-		int length);
-#endif
-
-
 	/*
 		Some handy methods
 	*/
+	void setDefaultAlphaMode()
+	{
+		switch (drawtype) {
+		case NDT_NORMAL:
+		case NDT_LIQUID:
+		case NDT_FLOWINGLIQUID:
+			alpha = ALPHAMODE_OPAQUE;
+			break;
+		case NDT_NODEBOX:
+		case NDT_MESH:
+			alpha = ALPHAMODE_LEGACY_COMPAT; // this should eventually be OPAQUE
+			break;
+		default:
+			alpha = ALPHAMODE_CLIP;
+			break;
+		}
+	}
+
 	bool needsBackfaceCulling() const
 	{
 		switch (drawtype) {
@@ -465,6 +478,21 @@ struct ContentFeatures
 	void updateTextures(ITextureSource *tsrc, IShaderSource *shdsrc,
 		scene::IMeshManipulator *meshmanip, Client *client, const TextureSettings &tsettings);
 #endif
+
+private:
+#ifndef SERVER
+	/*
+	 * Checks if any tile texture has any transparent pixels.
+	 * Prints a warning and returns true if that is the case, false otherwise.
+	 * This is supposed to be used for use_texture_alpha backwards compatibility.
+	 */
+	bool textureAlphaCheck(ITextureSource *tsrc, const TileDef *tiles,
+		int length);
+#endif
+
+	void setAlphaFromLegacy(u8 legacy_alpha);
+
+	u8 getAlphaForLegacy() const;
 };
 
 /*!

src/script/common/c_content.cpp

@@ -618,25 +618,39 @@ void read_content_features(lua_State *L, ContentFeatures &f, int index)
 	}
 	lua_pop(L, 1);
 
+	/* alpha & use_texture_alpha */
+	// This is a bit complicated due to compatibility
+
+	f.setDefaultAlphaMode();
+
 	warn_if_field_exists(L, index, "alpha",
-		"Obsolete, only limited compatibility provided");
+		"Obsolete, only limited compatibility provided; "
+		"replaced by \"use_texture_alpha\"");
 	if (getintfield_default(L, index, "alpha", 255) != 255)
-		f.alpha = 0;
+		f.alpha = ALPHAMODE_BLEND;
+
+	lua_getfield(L, index, "use_texture_alpha");
+	if (lua_isboolean(L, -1)) {
+		warn_if_field_exists(L, index, "use_texture_alpha",
+			"Boolean values are deprecated; use the new choices");
+		if (lua_toboolean(L, -1))
+			f.alpha = (f.drawtype == NDT_NORMAL) ? ALPHAMODE_CLIP : ALPHAMODE_BLEND;
+	} else if (check_field_or_nil(L, -1, LUA_TSTRING, "use_texture_alpha")) {
+		int result = f.alpha;
+		string_to_enum(ScriptApiNode::es_TextureAlphaMode, result,
+				std::string(lua_tostring(L, -1)));
+		f.alpha = static_cast<enum AlphaMode>(result);
+	}
+	lua_pop(L, 1);
 
-	bool usealpha = getboolfield_default(L, index,
-			"use_texture_alpha", false);
-	if (usealpha)
-		f.alpha = 0;
+	/* Other stuff */
 
-	// Read node color.
 	lua_getfield(L, index, "color");
 	read_color(L, -1, &f.color);
 	lua_pop(L, 1);
 
 	getstringfield(L, index, "palette", f.palette_name);
 
-	/* Other stuff */
-
 	lua_getfield(L, index, "post_effect_color");
 	read_color(L, -1, &f.post_effect_color);
 	lua_pop(L, 1);