Let FSkyboxTexture map to the last defined regular texture of the same name instead of its first face

This is normally a better fallback for the software renderer.

src/r_data/gldefs.cpp

@@ -102,7 +102,10 @@ static void ParseVavoomSkybox()
 			sc.ScriptError("%s: Skybox definition requires 6 faces", sb->GetName().GetChars());
 		}
 		sb->SetSize();
-		if (!error) TexMan.AddTexture(sb);
+		if (!error)
+		{
+			TexMan.AddTexture(sb);
+		}
 	}
 }
 
@@ -964,8 +967,7 @@ class GLDefsParser
 
 		sc.MustGetString();
 
-		FSkyBox * sb = new FSkyBox;
-		sb->Name = sc.String;
+		FSkyBox * sb = new FSkyBox(sc.String);
 		sb->Name.ToUpper();
 		if (sc.CheckString("fliptop"))
 		{

src/textures/skyboxtexture.cpp

@@ -36,8 +36,14 @@
 
 FSkyBox::FSkyBox(const char *name)
 : FTexture(name)
-{ 
-	faces[0]=faces[1]=faces[2]=faces[3]=faces[4]=faces[5]=NULL; 
+{
+	FTextureID texid = TexMan.CheckForTexture(name, ETextureType::Wall);
+	if (texid.isValid())
+	{
+		previous = TexMan.GetTexture(texid);
+		CopySize(previous);
+	}
+	faces[0]=faces[1]=faces[2]=faces[3]=faces[4]=faces[5] = nullptr;
 	UseType = ETextureType::Override;
 	bSkybox = true;
 	fliptop = false;
@@ -51,8 +57,7 @@ FSkyBox::FSkyBox(const char *name)
 
 TArray<uint8_t> FSkyBox::Get8BitPixels(bool alphatex)
 {
-	if (faces[0]) return faces[0]->Get8BitPixels(alphatex);
-	return FTexture::Get8BitPixels(alphatex);
+	return previous->Get8BitPixels(alphatex);
 }
 
 //-----------------------------------------------------------------------------
@@ -63,7 +68,16 @@ TArray<uint8_t> FSkyBox::Get8BitPixels(bool alphatex)
 
 FBitmap FSkyBox::GetBgraBitmap(PalEntry *p, int *trans)
 {
-	if (faces[0]) return faces[0]->GetBgraBitmap(p, trans);
-	return FTexture::GetBgraBitmap(p, trans);
+	return previous->GetBgraBitmap(p, trans);
 }
 
+//-----------------------------------------------------------------------------
+//
+//
+//
+//-----------------------------------------------------------------------------
+
+FImageSource *FSkyBox::GetImage() const
+{
+	return previous->GetImage();
+}

src/textures/skyboxtexture.h

@@ -12,18 +12,22 @@ class FSkyBox : public FTexture
 {
 public:
 
+	FTexture *previous;
 	FTexture * faces[6];
 	bool fliptop;
 
-	FSkyBox(const char *name = nullptr);
+	FSkyBox(const char *name);
 	TArray<uint8_t> Get8BitPixels(bool alphatex);
 	FBitmap GetBgraBitmap(PalEntry *, int *trans) override;
+	FImageSource *GetImage() const override;
+
 
 	void SetSize()
 	{
-		if (faces[0]) 
+		if (!previous && faces[0]) previous = faces[0];
+		if (previous)
 		{
-			CopySize(faces[0]);
+			CopySize(previous);
 		}
 	}
 
@@ -36,9 +40,4 @@ public:
 	{
 		return fliptop;
 	}
-
-	FImageSource *GetImage() const override
-	{
-		return faces[0] ? faces[0]->GetImage() : nullptr;
-	}
 };