Tile downsampling

[pkomon-tgm]

The compute pipeline will probably operate on tiles with a high zoom-level, therefore high resolution textures. This means, without any downsampling, the output will also be high resolution textures. Because it is not feasible for rendering to display all tiles on the high zoom levels, we need to downsample the tiles generated by the compute pipeline to generate lower resolution textures that can be used with lower zoom-level tiles.

This step should be done as a second compute pipeline. One problem is determining the tile-ids of the tiles that need to be created by the downsampling step. For now, I suggest we do this on the CPU (use the rectangular region of tiles of high zoom level to generated the set of low zoom-level tiles that fully covers it). Further, for generating even lower resolutions, we need the result of previous downsampling steps. Therefore, our downsampling compute pipeline can only do downsampling by one zoom level and we need multiple pipeline invocations for downsampling over multiple zoomlevels.

[pkomon-tgm]

• downsampling by single zoomlevels implemented in 860d463
• downsampling for multiple zoomlevels implemented in c1eab56