Hybrid Tiled Renderer

[obiot]

I have this mind for a long time, and seeing again performance issue with large maps that use the pre-rendering flag, I figured it would be good to bring it back on the table.

Basically today we have two different rendering mode :

• preRender true will render the whole layer on a offscreen canvas :that's fast as we only do 1 draw operation at the end, but very memory consuming on large maps (especially when using several layers)
• preRender false will render the visible part of the layer at each draw : slower than the above, as it's 1 draw operation per visible tile, but very memory optimized (no off-screen buffer is used)

Both have their advantages and ultimately we should provide something in between that brings the best of both :

• only render a portion of the map : ideally a "next power of 2" size compared to the viewport size (for performances reason)
• at each frame update, we translate the off-screen canvas by the camera offset and just draw the missing part

we could also make the off-screen size configurable so that we could tweak it for the best performances