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diff --git a/indra/newview/llworldmipmap.cpp b/indra/newview/llworldmipmap.cpp
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+/** 
+ * @file llworldmipmap.cpp
+ * @brief Data storage for the S3 mipmap of the entire world.
+ *
+ * $LicenseInfo:firstyear=2003&license=viewergpl$
+ * 
+ * Copyright (c) 2003-2009, Linden Research, Inc.
+ * 
+ * Second Life Viewer Source Code
+ * The source code in this file ("Source Code") is provided by Linden Lab
+ * to you under the terms of the GNU General Public License, version 2.0
+ * ("GPL"), unless you have obtained a separate licensing agreement
+ * ("Other License"), formally executed by you and Linden Lab.  Terms of
+ * the GPL can be found in doc/GPL-license.txt in this distribution, or
+ * online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
+ * 
+ * There are special exceptions to the terms and conditions of the GPL as
+ * it is applied to this Source Code. View the full text of the exception
+ * in the file doc/FLOSS-exception.txt in this software distribution, or
+ * online at
+ * http://secondlifegrid.net/programs/open_source/licensing/flossexception
+ * 
+ * By copying, modifying or distributing this software, you acknowledge
+ * that you have read and understood your obligations described above,
+ * and agree to abide by those obligations.
+ * 
+ * ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
+ * WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
+ * COMPLETENESS OR PERFORMANCE.
+ * $/LicenseInfo$
+ */
+
+#include "llviewerprecompiledheaders.h"
+
+#include "llworldmipmap.h"
+
+#include "llviewertexturelist.h"
+#include "math.h"	// log()
+
+// Turn this on to output tile stats in the standard output
+#define DEBUG_TILES_STAT 0
+
+LLWorldMipmap::LLWorldMipmap() :
+	mCurrentLevel(0)
+{
+}
+
+LLWorldMipmap::~LLWorldMipmap()
+{
+	reset();
+}
+
+// Delete all sublevel maps and clean them
+void LLWorldMipmap::reset()
+{
+	for (int level = 0; level < MAP_LEVELS; level++)
+	{
+		mWorldObjectsMipMap[level].clear();
+	}
+}
+
+// This method should be called before each use of the mipmap (typically, before each draw), so that to let
+// the boost level of unused tiles to drop to 0 (BOOST_NONE).
+// Tiles that are accessed have had their boost level pushed to BOOST_MAP_VISIBLE so we can identify them.
+// The result of this strategy is that if a tile is not used during 2 consecutive loops, its boost level drops to 0.
+void LLWorldMipmap::equalizeBoostLevels()
+{
+#if DEBUG_TILES_STAT
+	S32 nb_missing = 0;
+	S32 nb_tiles = 0;
+	S32 nb_visible = 0;
+#endif // DEBUG_TILES_STAT
+	// For each level
+	for (S32 level = 0; level < MAP_LEVELS; level++)
+	{
+		sublevel_tiles_t& level_mipmap = mWorldObjectsMipMap[level];
+		// For each tile
+		for (sublevel_tiles_t::iterator iter = level_mipmap.begin(); iter != level_mipmap.end(); iter++)
+		{
+			LLPointer<LLViewerFetchedTexture> img = iter->second;
+			S32 current_boost_level = img->getBoostLevel();
+			if (current_boost_level == LLViewerTexture::BOOST_MAP_VISIBLE)
+			{
+				// If level was BOOST_MAP_VISIBLE, the tile has been used in the last draw so keep it high
+				img->setBoostLevel(LLViewerTexture::BOOST_MAP);
+			}
+			else
+			{
+				// If level was BOOST_MAP only (or anything else...), the tile wasn't used in the last draw 
+				// so we drop its boost level to BOOST_NONE.
+				img->setBoostLevel(LLViewerTexture::BOOST_NONE);
+			}
+#if DEBUG_TILES_STAT
+			// Increment some stats if compile option on
+			nb_tiles++;
+			if (current_boost_level == LLViewerTexture::BOOST_MAP_VISIBLE)
+			{
+				nb_visible++;
+			}
+			if (img->isMissingAsset())
+			{
+				nb_missing++;
+			}
+#endif // DEBUG_TILES_STAT
+		}
+	}
+#if DEBUG_TILES_STAT
+	LL_INFOS("World Map") << "LLWorldMipmap tile stats : total requested = " << nb_tiles << ", visible = " << nb_visible << ", missing = " << nb_missing << LL_ENDL;
+#endif // DEBUG_TILES_STAT
+}
+
+// This method should be used when the mipmap is not actively used for a while, e.g., the map UI is hidden
+void LLWorldMipmap::dropBoostLevels()
+{
+	// For each level
+	for (S32 level = 0; level < MAP_LEVELS; level++)
+	{
+		sublevel_tiles_t& level_mipmap = mWorldObjectsMipMap[level];
+		// For each tile
+		for (sublevel_tiles_t::iterator iter = level_mipmap.begin(); iter != level_mipmap.end(); iter++)
+		{
+			LLPointer<LLViewerFetchedTexture> img = iter->second;
+			img->setBoostLevel(LLViewerTexture::BOOST_NONE);
+		}
+	}
+}
+
+LLPointer<LLViewerFetchedTexture> LLWorldMipmap::getObjectsTile(U32 grid_x, U32 grid_y, S32 level, bool load)
+{
+	// Check the input data
+	llassert(level <= MAP_LEVELS);
+	llassert(level >= 1);
+
+	// If the *loading* level changed, cleared the new level from "missed" tiles
+	// so that we get a chance to reload them
+	if (load && (level != mCurrentLevel))
+	{
+		cleanMissedTilesFromLevel(level);
+		mCurrentLevel = level;
+	}
+
+	// Build the region handle
+	U64 handle = convertGridToHandle(grid_x, grid_y);
+
+	// Check if the image is around already
+	sublevel_tiles_t& level_mipmap = mWorldObjectsMipMap[level-1];
+	sublevel_tiles_t::iterator found = level_mipmap.find(handle);
+
+	// If not there and load on, go load it
+	if (found == level_mipmap.end())
+	{
+		if (load)
+		{
+			// Load it 
+			LLPointer<LLViewerFetchedTexture> img = loadObjectsTile(grid_x, grid_y, level);
+			// Insert the image in the map
+			level_mipmap.insert(sublevel_tiles_t::value_type( handle, img ));
+			// Find the element again in the map (it's there now...)
+			found = level_mipmap.find(handle);
+		}
+		else
+		{
+			// Return with NULL if not found and we're not trying to load
+			return NULL;
+		}
+	}
+
+	// Get the image pointer and check if this asset is missing
+	LLPointer<LLViewerFetchedTexture> img = found->second;
+	if (img->isMissingAsset())
+	{
+		// Return NULL if asset missing
+		return NULL;
+	}
+	else
+	{
+		// Boost the tile level so to mark it's in use *if* load on
+		if (load)
+		{
+			img->setBoostLevel(LLViewerTexture::BOOST_MAP_VISIBLE);
+		}
+		return img;
+	}
+}
+
+LLPointer<LLViewerFetchedTexture> LLWorldMipmap::loadObjectsTile(U32 grid_x, U32 grid_y, S32 level)
+{
+	// Get the grid coordinates
+//	std::string imageurl = llformat("http://map.secondlife.com.s3.amazonaws.com/%d/%05d/%05d/map-%d-%d-%d-objects.jpg",
+	std::string imageurl = llformat("http://map.secondlife.com.s3.amazonaws.com/map-%d-%d-%d-objects.jpg",
+									level, grid_x, grid_y, level, grid_x, grid_y);
+
+	// DO NOT COMMIT!! DEBUG ONLY!!!
+	// Use a local jpeg for every tile to test map speed without S3 access
+	//imageurl = "file://C:\\Develop\\mapserver-distribute-3\\indra\\build-vc80\\mapserver\\relwithdebinfo\\regions\\00995\\01001\\region-995-1001-prims.jpg";
+	// END DEBUG
+	//LL_INFOS("World Map") << "LLWorldMipmap::loadObjectsTile(), URL = " << imageurl << LL_ENDL;
+
+	LLPointer<LLViewerFetchedTexture> img = LLViewerTextureManager::getFetchedTextureFromUrl(imageurl, TRUE, FALSE, LLViewerTexture::LOD_TEXTURE);
+	img->setBoostLevel(LLViewerTexture::BOOST_MAP);
+
+	// Return the smart pointer
+	return img;
+}
+
+// This method is used to clean up a level from tiles marked as "missing".
+// The idea is to allow tiles that have been improperly marked missing to be reloaded when retraversing the level again.
+// When zooming in and out rapidly, some tiles are never properly loaded and, eventually marked missing.
+// This creates "blue" areas in a subresolution that never got a chance to reload if we don't clean up the level.
+void LLWorldMipmap::cleanMissedTilesFromLevel(S32 level)
+{
+	// Check the input data
+	llassert(level <= MAP_LEVELS);
+	llassert(level >= 0);
+
+	// This happens when the object is first initialized
+	if (level == 0)
+	{
+		return;
+	}
+
+	// Iterate through the subresolution level and suppress the tiles that are marked as missing
+	// Note: erasing in a map while iterating through it is bug prone. Using a postfix increment is mandatory here.
+	sublevel_tiles_t& level_mipmap = mWorldObjectsMipMap[level-1];
+	sublevel_tiles_t::iterator it = level_mipmap.begin();
+	while (it != level_mipmap.end())
+	{
+		LLPointer<LLViewerFetchedTexture> img = it->second;
+		if (img->isMissingAsset())
+		{
+			level_mipmap.erase(it++);
+		}
+		else
+		{
+			++it;
+		}
+	}
+	return;
+}
+
+// static methods
+// Compute the level in the world mipmap (between 1 and MAP_LEVELS, as in the URL) given the scale (size of a sim in screen pixels)
+S32 LLWorldMipmap::scaleToLevel(F32 scale)
+{
+	// If scale really small, picks up the higest level there is (lowest resolution)
+	if (scale <= F32_MIN)
+		return MAP_LEVELS;
+	// Compute the power of two resolution level knowing the base level
+	S32 level = llfloor((log(REGION_WIDTH_METERS/scale)/log(2.0f)) + 1.0f);
+	// Check bounds and return the value
+	if (level > MAP_LEVELS)
+		return MAP_LEVELS;
+	else if (level < 1)
+		return 1;
+	else
+		return level;
+}
+
+// Convert world coordinates to mipmap grid coordinates at a given level (between 1 and MAP_LEVELS)
+void LLWorldMipmap::globalToMipmap(F64 global_x, F64 global_y, S32 level, U32* grid_x, U32* grid_y)
+{
+	// Check the input data
+	llassert(level <= MAP_LEVELS);
+	llassert(level >= 1);
+
+	// Convert world coordinates into grid coordinates
+	*grid_x = lltrunc(global_x/REGION_WIDTH_METERS);
+	*grid_y = lltrunc(global_y/REGION_WIDTH_METERS);
+	// Compute the valid grid coordinates at that level of the mipmap
+	S32 regions_in_tile = 1 << (level - 1);
+	*grid_x = *grid_x - (*grid_x % regions_in_tile);
+	*grid_y = *grid_y - (*grid_y % regions_in_tile);
+}
+
+