perf: Add some code paths to reduce transform calls.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # GeoJS Change Log
 
+## Version 1.8.7
+
+### Improvements
+
+- Add some code paths to reduce transform calls ([#1207](../../pull/1207))
+
 ## Version 1.8.6
 
 ### Improvements

src/transform.js

@@ -767,6 +767,21 @@ transform.vincentyDistance = function (pt1, pt2, gcs, baseGcs, ellipsoid, maxIte
   };
 };
 
+/**
+ * Return a boolean indicating if the projections only differ in their y
+ * coordinate.
+ *
+ * @param {string} srcPrj The source projection.
+ * @param {string} tgtPrj The destination projection.
+ * @returns {boolean} truthy if only the y coordinate is different between
+ *    projections.
+ */
+transform.onlyInvertedY = function (srcPrj, tgtPrj) {
+  const smatch = srcPrj.match(axisPattern),
+      tmatch = tgtPrj.match(axisPattern);
+  return smatch && tmatch && smatch[1] === tmatch[1] && smatch[3] === tmatch[3];
+};
+
 /* Expose proj4 to make it easier to debug */
 transform.proj4 = proj4;
 

src/webgl/lineFeature.js

@@ -134,6 +134,9 @@ var webgl_lineFeature = function (arg) {
           strokeOffset: 0, posStrokeOffset: 0, negStrokeOffset: 0
         }],
         v = vert[1],
+        target_gcs = m_this.gcs(),
+        map_gcs = m_this.layer().map().gcs(),
+        simpleInverse = transform.onlyInvertedY(target_gcs, map_gcs),
         pos, posIdx3, firstpos, firstPosIdx3,
         lineFunc = m_this.line(),
         strokeWidthFunc = m_this.style.get('strokeWidth'), strokeWidthVal,
@@ -188,7 +191,7 @@ var webgl_lineFeature = function (arg) {
         for (j = 0; j < lineItem.length; j += 1) {
           pos = posFunc(lineItem[j], j, d, i);
           position.push(pos.x);
-          position.push(pos.y);
+          position.push(simpleInverse ? -pos.y : pos.y);
           position.push(pos.z || 0.0);
           if (!j) {
             firstpos = pos;
@@ -208,8 +211,9 @@ var webgl_lineFeature = function (arg) {
         }
       }
 
-      position = transform.transformCoordinates(
-        m_this.gcs(), m_this.layer().map().gcs(), position, 3);
+      if (!simpleInverse) {
+        position = transform.transformCoordinates(target_gcs, map_gcs, position, 3);
+      }
       m_origin = new Float32Array(m_this.style.get('origin')(position));
       if (m_origin[0] || m_origin[1] || m_origin[2]) {
         for (i = 0; i < position.length; i += 3) {

src/webgl/polygonFeature.js

@@ -82,6 +82,7 @@ var webgl_polygonFeature = function (arg) {
         items = [],
         target_gcs = m_this.gcs(),
         map_gcs = m_this.layer().map().gcs(),
+        simpleInverse = transform.onlyInvertedY(target_gcs, map_gcs),
         numPts = 0,
         geom = m_mapper.geometryData(),
         color, opacity, fill, d, d3, vertices, i, j, k, n,
@@ -117,7 +118,7 @@ var webgl_polygonFeature = function (arg) {
         for (i = d3 = 0; i < outer.length; i += 1, d3 += 3) {
           c = posFunc(outer[i], i, item, itemIndex);
           geometry[d3] = c.x;
-          geometry[d3 + 1] = c.y;
+          geometry[d3 + 1] = simpleInverse ? -c.y : c.y;
           // ignore the z values until we support them
           geometry[d3 + 2] = 0;  // c.z || 0;
         }
@@ -134,20 +135,22 @@ var webgl_polygonFeature = function (arg) {
             for (i = 0; i < hole.length; i += 1, d3 += 3) {
               c = posFunc(hole[i], i, item, itemIndex);
               geometry.vertices[d3] = c.x;
-              geometry.vertices[d3 + 1] = c.y;
+              geometry.vertices[d3 + 1] = simpleInverse ? -c.y : c.y;
               // ignore the z values until we support them
               geometry.vertices[d3 + 2] = 0;  // c.z || 0;
             }
           });
         }
 
         // transform to map gcs
-        geometry.vertices = transform.transformCoordinates(
-          target_gcs,
-          map_gcs,
-          geometry.vertices,
-          geometry.dimensions
-        );
+        if (!simpleInverse) {
+          geometry.vertices = transform.transformCoordinates(
+            target_gcs,
+            map_gcs,
+            geometry.vertices,
+            geometry.dimensions
+          );
+        }
 
         record = {
           // triangulate