We used some shared SegmentVectors, e.g. for drawing raster or background tiles.
In longer running maps, this lead to resource accumulation. By storing the SegmentVectors
and the contained gfx::DrawScope objects, we ensure that resources get released
when the associated render objects vanish.
In cases when cached resource is useable, yet don't have an expiration
timestamp, we provided data to the requester from the cache and the same
data was returned once 304 response was received from the network.
What happened:
The excessive `onSpriteLoaded()` notifications were caused by the trick inside `OnlineFileRequest::completed()` implemenation,
which causes receving of two file source updates pointing to the *same* data in case the network response is `notModified` and
the local storage has the sprite sheet already stored inside.
In the SpriteLoader` implementation, it resulted in 2 extra `parseSprite()` calls and 2 extra `onSpriteLoaded()` notifications.
Then, the excessive `onSpriteLoaded()` notifications affected style images and all the unnecessarily added image dupes (btw,
the amount of these dupes `= 2 * number of style images`) were treated by the `RenderOrchestrator` as *updated* images.
Further, `RenderOrchestrator` called `ImageManager::updateImage()` for the updated images and the `ImageManager` populated the
`updatedImageVersions` map.
Finally, at every frame all the geometry tiles iterated through the `updatedImageVersions` to check whether their uploaded
textures needed patching.
All the mentioned above had a negative performance impact.
The fix:
Now, `SpriteLoader` sends `onSpriteLoaded()` notifications only if the data in the file source response is different comparing
to the existing one.
This change enables attaching images to the style with batches and
avoids massive re-allocations. Thus, it improves UI performance
especially at start-up time.
New setPrefetchZoomDelta(optional<uint8_t> delta) method allow overriding
default tile prefetch setting that is defined by the Map instance. The
method can be moved to generic style specification if found to be useful
for gl-js engine.
