Implement buffer_size overrides

[nyurik]

• implements Configurable tile buffer size override openmaptiles#1345
• partially implements Add support for extendable layer schema #377

Layer file changes

• Added support for an optional min_buffer_size value, which is only used in case of a global override, but if set, it must be less than or equal to buffer_size.
• Layer's buffer_size is now optional if min_buffer_size is set.

layer:
  id: housenumber
  # Only one of these is mandatory
  min_buffer_size: 1
  buffer_size: 8

Tileset file changes

• Added support for an optional overrides section (similar to defaults).
  • Only supports optional overrides.buffer_size int value for now. If set, this value will override the buffer_size set in the layer. If layer has min_buffer_size, the largest of the two will be used.
• Added support for per layer overrides as described in Add support for extendable layer schema #377. Only supports buffer_size and min_buffer_size
• An environment variable TILE_BUFFER_SIZE can be used instead of overrides.buffer_size, and it takes precedence.

This example will load two layers. Mountain peak will be used as is, and house numbers's min buffer zoom is modified. The global override=0 will set mountain peaks buffer to 0 (because it has no min_buffer_size defined inside the layer file), but the house number buffer size will be 5.

tileset:
  layers:
    - mountain_peak/mountain_peak.yaml
    - file: housenumber/housenumber.yaml
      min_buffer_size: 5
  overrides:
    buffer_size: 0

Breaking

• Remove deprecated tileset and layer properties (they have been deprecated for many years, and are not used)

[farfromrefug]

@nyurik this look pretty awesome!

[zstadler]

My understanding is that min_buffer_size is also used with per-layer override.

Suggested change

	min_buffer_size is only used when there is a global buffer size override,
	`min_buffer_size` is only used when there is a `buffer_size` override.

[zstadler]

My understanding of this sentence is that env. variable has higher priority than per-layer min_buffer_size override.

Suggested change

	Per layer overrides have higher priority than global overrides, but less than ENV var.
	Per layer `buffer_size` override has a higher priority than a global override, but less than ENV var.
	Per layer `min_buffer_size` tileset override has a higher priority than the layer's `min_buffer_size`.
	The resulting `min_buffer_size` is used if it is higher that the resulting `buffer_size`.

As far as I understand the code, the final buffer size of a layer is

max(
  first_of(
    TILE_BUFFER_SIZE environment variable,
    layer-specific override of the `buffer_size`,
    global override of the `buffer_size`,
    layer's `buffer_size`,
    layer's min_buffer_size,
    0),
  first_of(
    layer-specific override of min_buffer_size,
    global override of min_buffer_size,
    layer's min_buffer_size )
)

[nyurik]

Not exactly, the overrides follow this logic (or at least it should):

        max(
          first_found_value(
            TILE_BUFFER_SIZE env variable,
            buffer_size set in the tileset yaml file layer's section (per layer override),
            buffer_size set in the tileset yaml file at the top level (global override),
            buffer_size set in the layer yaml file,
            0),
          first_found_value(
            min_buffer_size set in the tileset yaml file layer's section (per layer override),
            min_buffer_size set in the layer yaml file,
            0)
        )

Note that there is no global min_buffer_size override as that has very little value IMO. Also, while there is a fallback to 0 for both, the layer file requires either one to be present. Lastly, both vars are computed independently until the very end.

[nyurik]

tried to cleanup buffer size logic/docs, thx for feedback!

[nyurik]

Not exactly, the overrides follow this logic (or at least it should):

        max(
          first_found_value(
            TILE_BUFFER_SIZE env variable,
            buffer_size set in the tileset yaml file layer's section (per layer override),
            buffer_size set in the tileset yaml file at the top level (global override),
            buffer_size set in the layer yaml file,
            0),
          first_found_value(
            min_buffer_size set in the tileset yaml file layer's section (per layer override),
            min_buffer_size set in the layer yaml file,
            0)
        )

Note that there is no global min_buffer_size override as that has very little value IMO. Also, while there is a fallback to 0 for both, the layer file requires either one to be present. Lastly, both vars are computed independently until the very end.