[Marble-devel] [Patch] Add class TileId because int is not sufficient for higher zoom levels

[Torsten Rahn]

On Thursday 24 April 2008 22:17:21 Jens-Michael Hoffmann wrote:

Hi,

I like the approach however I've also done some performance measurement and on 
my computer I get a performance difference between 15.9fps before applying 
the patch and 11.48 fps after applying the patch. That's a performance 
decrease of 28% which unfortunately isn't acceptable. :-/ 

So we've got to find some less expensive solution here.

Looking at the patch I'd bet that the problematic lines are in TileLoader.cpp 
line 183 ff as these get called very often during rendering:

Your new implementation creates a new tileId object each time the method is 
called and searching the hash and the cache requires a lot of overhead by 
introducing a lot more rather expensive comparisons to do: 


    TileId tileId( tileLevel, tilx, tily );


    // If the tile hasn't been loaded into the m_tileHash yet, then do so...
    if ( !d->m_tileHash.contains( tileId ) ) {
        if ( d->m_tileCache.contains( tileId ) ) {
            tile = d->m_tileCache.take( tileId );
            d->m_tileHash[tileId] = tile;

Maybe as a workaround you could compare or lookup tileId's by pointers or by 
a "temporary" Id which just gets assigned to each tile while the tile is 
located in the hash/cache. This would effectively get us back to an int 
comparison and hence remove the speed penalty of this feature.

Best Wishes,

Torsten


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