Allow empty actor files.

This allows empty actor files -> they map to a dummy object that renders
nothing.
The use case is automatically hiding objects at lower quality levels &
LOD settings.

Differential Revision: https://code.wildfiregames.com/D3819
This was SVN commit r25224.

source/graphics/ModelAbstract.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2019 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -23,6 +23,7 @@
 #include "maths/BoundingBoxOriented.h"
 #include "simulation2/helpers/Player.h"
 
+class CModelDummy;
 class CModel;
 class CModelDecal;
 class CModelParticleEmitter;
@@ -73,13 +74,16 @@ public:
 	virtual CModelAbstract* Clone() const = 0;
 
 	/// Dynamic cast
-	virtual CModel* ToCModel() { return NULL; }
+	virtual CModelDummy* ToCModelDummy() { return nullptr; }
 
 	/// Dynamic cast
-	virtual CModelDecal* ToCModelDecal() { return NULL; }
+	virtual CModel* ToCModel() { return nullptr; }
 
 	/// Dynamic cast
-	virtual CModelParticleEmitter* ToCModelParticleEmitter() { return NULL; }
+	virtual CModelDecal* ToCModelDecal() { return nullptr; }
+
+	/// Dynamic cast
+	virtual CModelParticleEmitter* ToCModelParticleEmitter() { return nullptr; }
 
 	// (This dynamic casting is a bit ugly, but we won't have many subclasses
 	// and this seems the easiest way to integrate with other code that wants

source/graphics/ModelDummy.h

@@ -0,0 +1,45 @@
+/* Copyright (C) 2021 Wildfire Games.
+ * This file is part of 0 A.D.
+ *
+ * 0 A.D. is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 0 A.D. is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef INCLUDED_MODELDUMMY
+#define INCLUDED_MODELDUMMY
+
+#include "graphics/ModelAbstract.h"
+
+/**
+ * Empty placeholder ModelAbstract implementation, to render nothing.
+ */
+class CModelDummy final : public CModelAbstract
+{
+	NONCOPYABLE(CModelDummy);
+
+public:
+
+	CModelDummy() = default;
+	virtual ~CModelDummy() = default;
+
+	virtual CModelAbstract* Clone() const { return new CModelDummy(); }
+	virtual CModelDummy* ToCModelDummy() { return this; }
+
+	virtual void CalcBounds() {};
+	virtual void SetDirtyRec(int) {};
+	virtual void SetTerrainDirty(ssize_t, ssize_t, ssize_t, ssize_t) {}
+	virtual void ValidatePosition() {};
+	virtual void InvalidatePosition() {};
+};
+
+#endif // INCLUDED_MODELDUMMY

source/graphics/ObjectEntry.cpp

@@ -25,6 +25,7 @@
 #include "graphics/MeshManager.h"
 #include "graphics/Model.h"
 #include "graphics/ModelDef.h"
+#include "graphics/ModelDummy.h"
 #include "graphics/ObjectBase.h"
 #include "graphics/ObjectManager.h"
 #include "graphics/ParticleManager.h"
@@ -77,6 +78,12 @@ bool CObjectEntry::BuildVariation(const std::vector<const std::set<CStr>*>& comp
 			m_Color = CColor(r/255.0f, g/255.0f, b/255.0f, 1.0f);
 	}
 
+	if (variation.model.empty())
+	{
+		m_Model = new CModelDummy();
+		return true;
+	}
+
 	if (variation.decal.m_SizeX && variation.decal.m_SizeZ)
 	{
 		CMaterial material = g_Renderer.GetMaterialManager().LoadMaterial(m_Base->m_Material);

source/renderer/Scene.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2011 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -55,6 +55,9 @@ void SceneCollector::SubmitRecursive(CModelAbstract* model)
 	{
 		Submit(model->ToCModelParticleEmitter()->m_Emitter.get());
 	}
+	else if (model->ToCModelDummy())
+	{
+	}
 	else
 		debug_warn(L"unknown model type");
 }