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Render empty tiles outside of area of interest

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This commit is contained in:
Tom Russell 2019-02-24 20:07:22 +00:00
parent 2d8b62fb84
commit 5392ad0606
2 changed files with 32 additions and 7 deletions
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2
app/src/tiles/tile.js
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@ -189,4 +189,4 @@ function get_highlight_table_def(geometry_id) {
}
export { get_bbox, get_xyz, render_tile };
export { get_bbox, get_xyz, render_tile, TILE_SIZE };

37
app/src/tiles/tileserver.js
View File

@ -6,9 +6,17 @@ import express from 'express';
import sharp from 'sharp';
import { get, put } from './cache';
import { render_tile, get_bbox, get_xyz } from './tile';
import { render_tile, get_bbox, get_xyz, TILE_SIZE } from './tile';
import { strictParseInt } from '../parse';
// zoom level when we switch from rendering direct from database to instead composing tiles
// from the zoom level below - gets similar effect, with much lower load on Postgres
const STITCH_THRESHOLD = 12
// Hard-code extent so we can short-circuit rendering and return empty/transparent tiles outside the area of interest
// bbox in CRS espg:3957 in form: [w, s, e, n]
const EXTENT_BBOX = [-61149.622628, 6667754.851372, 28128.826409, 6744803.375884]
// tiles router
const router = express.Router()
@ -63,6 +71,9 @@ function handle_tile_request(tileset, req, res) {
}
function load_tile(tileset, z, x, y) {
if (outside_extent(z, x, y)) {
return empty_tile()
}
return new Promise((resolve) => {
get(tileset, z, x, y, (err, im) => {
if (err) {
@ -79,9 +90,7 @@ function load_tile(tileset, z, x, y) {
}
function render_or_stitch_tile(tileset, z, x, y) {
const STITCH_THRESHOLD = 12
if (z <= STITCH_THRESHOLD) {
return stitch_tile(tileset, z, x, y).then(im => {
return new Promise((resolve, reject) => {
put(im, tileset, z, x, y, (err) => {
@ -115,6 +124,22 @@ function render_or_stitch_tile(tileset, z, x, y) {
}
}
function outside_extent(z, x, y) {
const xy = get_xyz(EXTENT_BBOX, z);
return xy.minY > y || xy.maxY < y || xy.minX > x || xy.maxX < x;
}
function empty_tile() {
return sharp({
create: {
width: TILE_SIZE,
height: TILE_SIZE,
channels: 4,
background: { r: 0, g: 0, b: 0, alpha: 0 }
}
}).png().toBuffer()
}
function stitch_tile(tileset, z, x, y) {
const bbox = get_bbox(z, x, y)
const next_z = z + 1
@ -137,8 +162,8 @@ function stitch_tile(tileset, z, x, y) {
// instead of repeatedly creating `sharp` objects, to png, to buffer...
return sharp({
create: {
width: 512,
height: 512,
width: TILE_SIZE * 2,
height: TILE_SIZE * 2,
channels: 4,
background: { r: 0, g: 0, b: 0, alpha: 0 }
}
@ -158,7 +183,7 @@ function stitch_tile(tileset, z, x, y) {
).png().toBuffer()
}).then((buf) => {
return sharp(buf
).resize(256, 256, { fit: 'inside' }
).resize(TILE_SIZE, TILE_SIZE, { fit: 'inside' }
).png().toBuffer()
})
});