[core] - initialise frame_history with an out of range zoom value

[tobrun]

Closes #6667.

This PR initialises previousZoomIndex with -1 instead of 0 in frame_history.cpp. Solves the issue that painter->needsAnimation() keeps on returning true when a map is initialised with the default camera location. This currently results in constantly rerendering the map.

Below you can see it stops using cpu resources vs the before screenshot.

More information in #6667.

Review @kkaefer

[mention-bot]

@tobrun, thanks for your PR! By analyzing the history of the files in this pull request, we identified @ansis, @kkaefer and @brunoabinader to be potential reviewers.

[kkaefer]

There's already a variable called firstFrame. Can we use that to detect the presence of the first frame rendered?

[tobrun]

@kkaefer thank you for 👀 , will attempt to make it work with firstFrame.

[tobrun]

@kkaefer in f2b8339 I proposed an alternative solution. The underlying issue is that the following if check never returns true and thus never setting the previous time.

    if (zoomIndex != previousZoomIndex) {
        previousZoomIndex = zoomIndex;
        previousTime = now;
    }

In f2b8339 I'm setting the previousTime when the firstFrame is going to be rendered. This solves the issue that needsAnimation keeps returning true.

Do you feel this is a better approach?

[tobrun]

closing in favour of #6979