Merge pull request #1220 from OpenGeoscience/speed-up-tracks

perf: Speed up track feature.

src/lineFeature.js

@@ -46,9 +46,12 @@ var util = require('./util');
  *   divided by the sine of half the angle between segments, then a bevel join
  *   is used instead.  This is a single value that applies to all lines.  If a
  *   function, it is called with `(data)`.
- * @property {boolean|function} [uniformLine=false] Boolean indicating if each
- *   line has a uniform style (uniform stroke color, opacity, and width).  Can
- *   vary by line.
+ * @property {boolean|string|function} [uniformLine=false] Boolean indicating
+ *   if each line has a uniform style (uniform stroke color, opacity, and
+ *   width).  Can vary by line.  A value of `'drop'` will modify rendered
+ *   vertex order by dropping duplicates and setting later values to zero
+ *   opacity.  This can be faster but makes it so updating the style array
+ *   can no longer be used.
  * @property {number|function} [antialiasing] Antialiasing distance in pixels.
  *   Values must be non-negative.  A value greater than 1 will produce a
  *   visible gradient.  This is a single value that applies to all lines.

src/trackFeature.js

@@ -816,7 +816,9 @@ var trackFeature = function (arg) {
       {
         track: util.identityFunction,
         position: util.identityFunction,
-        time: (d, i) => (d.t !== undefined ? d.t : i)
+        time: (d, i) => (d.t !== undefined ? d.t : i),
+        uniformLine: 'drop',
+        closed: false
       },
       arg.style === undefined ? {} : arg.style
     );

src/webgl/lineFeature.js

@@ -269,6 +269,7 @@ var webgl_lineFeature = function (arg) {
       closedVal = closed[i];
       firstPosIdx3 = posIdx3;
       maxj = lineItem.length + (closedVal === 2 ? 1 : 0);
+      let skipped = 0;
       for (j = 0; j < maxj; j += 1, posIdx3 += 3) {
         lidx = j;
         if (j === lineItem.length) {
@@ -329,9 +330,17 @@ var webgl_lineFeature = function (arg) {
         }
 
         if (j) {
+          if (uniform === 'drop' && j > 1 && position[vert[0].pos] === position[vert[1].pos] && position[vert[0].pos + 1] === position[vert[1].pos + 1]) {
+            skipped += 1;
+            continue;
+          }
           /* zero out the z position.  This can be changed if we handle it in
            * the shader. */
           for (k = 0; k < orderLen; k += 1, dest += 1, dest3 += 3) {
+            if (uniform === 'drop' && vert[0].strokeOpacity <= 0 && vert[1].strokeOpacity <= 0) {
+              strokeOpacityBuf[dest] = -1;
+              continue;
+            }
             orderk0 = order[k][0];
             v1 = vert[orderk0];
             v2 = vert[1 - orderk0];
@@ -370,6 +379,11 @@ var webgl_lineFeature = function (arg) {
           }
         }
       }
+      if (skipped) {
+        for (k = 0; k < skipped * orderLen; k += 1, dest += 1, dest3 += 3) {
+          strokeOpacityBuf[dest] = -1;
+        }
+      }
     }
 
     if (!onlyStyle) {