From d6db27e633b1b8850fb093a8e5fad439ac3b0465 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 30 Jan 2021 20:03:47 +0200
Subject: [PATCH] Improve allocation handling in cube map textures

While there isn't enough bits to track all face allocations, tracking
the base level per face is possible.  This allows mipmap generation to
work more sensibly.
---
 source/texturecube.cpp | 27 ++++++++++++++++++++-------
 source/texturecube.h   |  2 ++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/source/texturecube.cpp b/source/texturecube.cpp
index 82447e65..14ddf43d 100644
--- a/source/texturecube.cpp
+++ b/source/texturecube.cpp
@@ -71,7 +71,7 @@ void TextureCube::allocate(unsigned level)
 		throw invalid_operation("TextureCube::allocate");
 	if(level>=levels)
 		throw invalid_argument("TextureCube::allocate");
-	if(allocated&(1<<level))
+	if(allocated&(64<<level))
 		return;
 
 	if(ARB_texture_storage)
@@ -107,13 +107,26 @@ void TextureCube::image(TextureCubeFace face, unsigned level, PixelFormat fmt, D
 		glTexParameteri(target, GL_TEXTURE_MAX_LEVEL, levels-1);
 	glTexImage2D(face, level, ifmt, s, s, 0, get_upload_format(fmt), type, data);
 
-	// XXX Allocation should be tracked per-face, but we'll run out of bits
-	allocated |= 1<<level;
-	if(auto_gen_mipmap && level==0)
+	if(level==0)
 	{
-		// TODO Only do this once all faces are created
-		generate_mipmap();
-		allocated |= (1<<levels)-1;
+		allocated |= 1<<get_face_index(face);
+		if((allocated&63)==63)
+		{
+			allocated |= 64;
+			if(auto_gen_mipmap)
+			{
+				generate_mipmap();
+				allocated |= (64<<levels)-1;
+			}
+		}
+	}
+	else if(!(allocated&(64<<level)))
+	{
+		for(unsigned i=0; i<6; ++i)
+			if(enumerate_faces(i)!=face)
+				glTexImage2D(enumerate_faces(i), level, ifmt, s, s, 0, get_upload_format(fmt), type, 0);
+
+		allocated |= 64<<level;
 	}
 }
 
diff --git a/source/texturecube.h b/source/texturecube.h
index f5a36404..dabf2b88 100644
--- a/source/texturecube.h
+++ b/source/texturecube.h
@@ -51,6 +51,8 @@ public:
 private:
 	unsigned size;
 	unsigned levels;
+	/* Lowest six bits track allocation status of faces on the base level.  Bit
+	seven is set if the entire base level is allocated. */
 	unsigned allocated;
 
 	static TextureCubeFace face_order[6];
-- 
2.43.0