Add "bits" parameter to "loadGeometry" (#2858)

* Add "bits" parameter to "loadGeometry"

* Eliminate magic numbers

* Simplify loadGeometry bounds lookup

js/data/bucket/line_bucket.js

@@ -28,15 +28,15 @@ var COS_HALF_SHARP_CORNER = Math.cos(75 / 2 * (Math.PI / 180));
 var SHARP_CORNER_OFFSET = 15;
 
 // The number of bits that is used to store the line distance in the buffer.
-var LINE_DISTANCE_BUFFER_BITS = 14;
+var LINE_DISTANCE_BUFFER_BITS = 15;
 
 // We don't have enough bits for the line distance as we'd like to have, so
 // use this value to scale the line distance (in tile units) down to a smaller
 // value. This lets us store longer distances while sacrificing precision.
 var LINE_DISTANCE_SCALE = 1 / 2;
 
 // The maximum line distance, in tile units, that fits in the buffer.
-var MAX_LINE_DISTANCE = Math.pow(2, LINE_DISTANCE_BUFFER_BITS) / LINE_DISTANCE_SCALE;
+var MAX_LINE_DISTANCE = Math.pow(2, LINE_DISTANCE_BUFFER_BITS - 1) / LINE_DISTANCE_SCALE;
 
 
 module.exports = LineBucket;
@@ -86,7 +86,7 @@ LineBucket.prototype.programInterfaces = {
 };
 
 LineBucket.prototype.addFeature = function(feature) {
-    var lines = loadGeometry(feature);
+    var lines = loadGeometry(feature, LINE_DISTANCE_BUFFER_BITS);
     for (var i = 0; i < lines.length; i++) {
         this.addLine(
             lines[i],

js/data/load_geometry.js

@@ -1,17 +1,39 @@
 'use strict';
 
 var util = require('../util/util');
-
 var EXTENT = require('./bucket').EXTENT;
-var EXTENT_MIN = EXTENT * -2;
-var EXTENT_MAX = (EXTENT * 2) - 1;
+var assert = require('assert');
+
+
+// These bounds define the minimum and maximum supported coordinate values.
+// While visible coordinates are within [0, EXTENT], tiles may theoretically
+// contain cordinates within [-Infinity, Infinity]. Our range is limited by the
+// number of bits used to represent the coordinate.
+function createBounds(bits) {
+    return {
+        min: -1 * Math.pow(2, bits - 1),
+        max: Math.pow(2, bits - 1) - 1
+    };
+}
+
+var boundsLookup = {
+    15: createBounds(15),
+    16: createBounds(16)
+};
 
 /**
  * Loads a geometry from a VectorTileFeature and scales it to the common extent
  * used internally.
+ * @param {VectorTileFeature} feature
+ * @param {number} [bits=16] The number of signed integer bits available to store
+ *   each coordinate. A warning will be issued if any coordinate will not fits
+ *   in the specified number of bits.
  * @private
  */
-module.exports = function loadGeometry(feature) {
+module.exports = function loadGeometry(feature, bits) {
+    var bounds = boundsLookup[bits || 16];
+    assert(bounds);
+
     var scale = EXTENT / feature.extent;
     var geometry = feature.loadGeometry();
     for (var r = 0; r < geometry.length; r++) {
@@ -22,11 +44,8 @@ module.exports = function loadGeometry(feature) {
             // points and we need to do the same to avoid renering differences.
             point.x = Math.round(point.x * scale);
             point.y = Math.round(point.y * scale);
-            if (
-                point.x < EXTENT_MIN ||
-                point.x > EXTENT_MAX ||
-                point.y < EXTENT_MIN ||
-                point.y > EXTENT_MAX) {
+
+            if (point.x < bounds.min || point.x > bounds.max || point.y < bounds.min || point.y > bounds.max) {
                 util.warnOnce('Geometry exceeds allowed extent, reduce your vector tile buffer size');
             }
         }

test/js/data/load_geometry.test.js

@@ -33,7 +33,7 @@ test('loadGeometry extent error', function(t) {
         }
     };
 
-    loadGeometry(feature);
+    loadGeometry(feature, 15);
 
     t.equal(numWarnings, 1);
 
@@ -42,4 +42,3 @@ test('loadGeometry extent error', function(t) {
 
     t.end();
 });
-