Always add first segment when appending coordinates

When we have only a single point, we want to make sure it gets added (fixes #1821).

Because this code doesn't differentiate coordinates that are part of a linestring or linearring from those that are independent points, we always add the first segment (or pair of points).  In addition, coordinates for segments are appended whenever they represent a change in relationship with respect to the extent.  This keeps the code simpler for handling fills and properly capturing intersection points for linestrings.  This could be modified to save a few extra coordinates, but it provides for simpler code at a very minimal cost.

src/ol/render/canvas/canvasreplay.js

@@ -2,6 +2,7 @@
 // FIXME add option to apply snapToPixel to all coordinates?
 // FIXME can eliminate empty set styles and strokes (when all geoms skipped)
 
+goog.provide('ol.render.canvas.Replay');
 goog.provide('ol.render.canvas.ReplayGroup');
 
 goog.require('goog.array');
@@ -166,6 +167,12 @@ ol.render.canvas.Replay.prototype.appendFlatCoordinates =
     lastRel = nextRel;
   }
 
+  // handle case where there is only one point to append
+  if (i === offset + stride) {
+    this.coordinates[myEnd++] = lastCoord[0];
+    this.coordinates[myEnd++] = lastCoord[1];
+  }
+
   if (close) {
     this.coordinates[myEnd++] = flatCoordinates[offset];
     this.coordinates[myEnd++] = flatCoordinates[offset + 1];

test/spec/ol/renderer/canvas/canvasreplay.test.js

@@ -0,0 +1,81 @@
+goog.provide('ol.test.renderer.canvas.Replay');
+
+describe('ol.render.canvas.Replay', function() {
+
+  describe('constructor', function() {
+
+    it('creates a new replay batch', function() {
+      var tolerance = 10;
+      var extent = [-180, -90, 180, 90];
+      var replay = new ol.render.canvas.Replay(tolerance, extent);
+      expect(replay).to.be.a(ol.render.canvas.Replay);
+    });
+
+  });
+
+  describe('#appendFlatCoordinates()', function() {
+
+    var replay;
+    beforeEach(function() {
+      replay = new ol.render.canvas.Replay(1, [-180, -90, 180, 90]);
+    });
+
+    it('appends coordinates that are within the max extent', function() {
+      var flat = [-110, 45, 110, 45, 110, -45, -110, -45];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('works with a single coordinate (inside)', function() {
+      var flat = [-110, 45];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('always appends first point (even if outside)', function() {
+      // this could be changed, but to make the code simpler for properly
+      // closing rings, we always add the first point
+      var flat = [-110, 145];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('appends points when segments cross (top to bottom)', function() {
+      // this means we get a few extra points when coordinates are not
+      // part of a linestring or ring, but only a few extra
+      var flat = [0, 200, 0, -200];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('appends points when segments cross (top to inside)', function() {
+      var flat = [0, 200, 0, 0];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('always appends the first segment (even when outside)', function() {
+      // this could be changed, but to make the code simpler for properly
+      // closing rings, we always add the first segment
+      var flat = [-10, 200, 10, 200];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql(flat);
+    });
+
+    it('eliminates segments outside (and not changing rel)', function() {
+      var flat = [0, 0, 0, 200, 10, 200];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql([0, 0, 0, 200]);
+    });
+
+    it('includes outside segments that change relationship', function() {
+      var flat = [0, 0, 0, 200, 200, 200, 250, 200];
+      replay.appendFlatCoordinates(flat, 0, flat.length, 2, false);
+      expect(replay.coordinates).to.eql([0, 0, 0, 200, 200, 200]);
+    });
+
+  });
+
+});
+
+goog.require('ol.render.canvas.Replay');