Fixed a signed / unsigned error.  The pixel coordinates are scaled verisons of the world coordinates are are allowed to be negative.  The camera is smart enough to write to the correct pixels.
Smaller tile size means faster turnaround.  YES.  This is the step towards interactivity I needed to see progress.  I'd like the UI to control this, but for now it is hardcoded in two places.
Changed argument order to x0,y0 x1,y1.  This makes more sense to me.
Attempt to recenter viewplane for mars, will make next changes in the editor.
Added Gamma correction and fixed odd discontinuities in color across tiles.
My understanding of unique_ptrs has grown.  The Scene is the owner of the pointers and should be passed by value to better reflect that.
Fixed the new bug where tiles that crossed 0 were not being rendered, sheesh
No more image caching.  JS tiling uses MD5 for image urls now, loading a new scene actually works now.