Simplify triangle-shifting logic for reprojection

src/ol/reproj/reproj.js

@@ -49,6 +49,7 @@ ol.reproj.calculateSourceResolution = function(sourceProj, targetProj,
  * Renders the source into the canvas based on the triangulation.
  * @param {CanvasRenderingContext2D} context
  * @param {number} sourceResolution
+ * @param {ol.Extent} sourceExtent
  * @param {number} targetResolution
  * @param {ol.Extent} targetExtent
  * @param {ol.reproj.Triangulation} triangulation
@@ -56,9 +57,13 @@ ol.reproj.calculateSourceResolution = function(sourceProj, targetProj,
  *                 image: (HTMLCanvasElement|Image)}>} sources
  */
 ol.reproj.renderTriangles = function(context,
-    sourceResolution, targetResolution, targetExtent, triangulation, sources) {
+    sourceResolution, sourceExtent, targetResolution, targetExtent,
+    triangulation, sources) {
 
-  var shiftDistance = triangulation.shiftDistance;
+  var shiftDistance = !goog.isNull(sourceExtent) ?
+      ol.extent.getWidth(sourceExtent) : null;
+  var shiftThreshold = !goog.isNull(sourceExtent) ?
+      (sourceExtent[0] + sourceExtent[2]) / 2 : null;
   var targetTL = ol.extent.getTopLeft(targetExtent);
 
   goog.array.forEach(triangulation.triangles, function(tri, i, arr) {
@@ -91,10 +96,10 @@ ol.reproj.renderTriangles = function(context,
     var u0 = tgt[0][0] - targetTL[0], v0 = -(tgt[0][1] - targetTL[1]),
         u1 = tgt[1][0] - targetTL[0], v1 = -(tgt[1][1] - targetTL[1]),
         u2 = tgt[2][0] - targetTL[0], v2 = -(tgt[2][1] - targetTL[1]);
-    if (tri.needsShift) {
-      x0 = goog.math.modulo(x0 + shiftDistance, shiftDistance);
-      x1 = goog.math.modulo(x1 + shiftDistance, shiftDistance);
-      x2 = goog.math.modulo(x2 + shiftDistance, shiftDistance);
+    if (tri.needsShift && !goog.isNull(shiftDistance)) {
+      x0 = goog.math.modulo(x0, shiftDistance);
+      x1 = goog.math.modulo(x1, shiftDistance);
+      x2 = goog.math.modulo(x2, shiftDistance);
     }
     var augmentedMatrix = [
       [x0, y0, 1, 0, 0, 0, u0 / targetResolution],
@@ -142,8 +147,9 @@ ol.reproj.renderTriangles = function(context,
       var dataTL = ol.extent.getTopLeft(src.extent);
       context.translate(dataTL[0], dataTL[1]);
       // if the triangle needs to be shifted (because of the dateline wrapping),
-      // shift only the source images that need it
-      if (tri.needsShift && dataTL[0] < 0) {
+      // shift back only the source images that need it
+      if (tri.needsShift && !goog.isNull(shiftDistance) &&
+          dataTL[0] < shiftThreshold) {
         context.translate(shiftDistance, 0);
       }
       context.scale(sourceResolution, -sourceResolution);

src/ol/reproj/tile.js

@@ -114,7 +114,8 @@ ol.reproj.Tile = function(sourceProj, sourceTileGrid,
   }
 
   this.srcZ_ = sourceTileGrid.getZForResolution(sourceResolution);
-  var srcExtent = ol.reproj.triangulation.getSourceExtent(this.triangulation_);
+  var srcExtent = ol.reproj.triangulation.getSourceExtent(
+      this.triangulation_, sourceProj);
 
   var sourceProjExtent = sourceProj.getExtent();
   if (!sourceProj.isGlobal() && sourceProjExtent) {
@@ -238,8 +239,9 @@ ol.reproj.Tile.prototype.reproject_ = function() {
 
   if (sources.length > 0) {
     var targetExtent = this.targetTileGrid_.getTileCoordExtent(tileCoord);
-    ol.reproj.renderTriangles(context, srcResolution, targetResolution,
-                              targetExtent, this.triangulation_, sources);
+    ol.reproj.renderTriangles(context,
+        srcResolution, this.sourceTileGrid_.getExtent(),
+        targetResolution, targetExtent, this.triangulation_, sources);
   }
 
   this.canvas_ = context.canvas;

src/ol/reproj/triangulation.js

@@ -22,8 +22,10 @@ ol.reproj.Triangle;
 
 
 /**
+ * `needsShift` indicates that _any_ of the triangles has to be shifted during
+ *  reprojection. See {@link ol.reproj.Triangle}.
  * @typedef {{triangles: Array.<ol.reproj.Triangle>,
- *            shiftDistance: number}}
+ *            needsShift: boolean}}
  */
 ol.reproj.Triangulation;
 
@@ -101,8 +103,7 @@ ol.reproj.triangulation.addTriangleIfValid_ = function(triangulation, a, b, c,
     needsShift: needsShift
   });
   if (needsShift) {
-    var sourceProjExtent = sourceProj.getExtent();
-    triangulation.shiftDistance = ol.extent.getWidth(sourceProjExtent);
+    triangulation.needsShift = true;
   }
 };
 
@@ -123,7 +124,7 @@ ol.reproj.triangulation.createForExtent = function(extent, sourceProj,
 
   var triangulation = {
     triangles: [],
-    shiftDistance: 0
+    needsShift: false
   };
 
   var tlDst = ol.extent.getTopLeft(extent);
@@ -167,24 +168,32 @@ ol.reproj.triangulation.createForExtent = function(extent, sourceProj,
 
 /**
  * @param {ol.reproj.Triangulation} triangulation
+ * @param {ol.proj.Projection} sourceProj
  * @return {ol.Extent}
  */
-ol.reproj.triangulation.getSourceExtent = function(triangulation) {
+ol.reproj.triangulation.getSourceExtent = function(triangulation, sourceProj) {
   var extent = ol.extent.createEmpty();
 
-  var distance = triangulation.shiftDistance;
-  if (distance > 0) {
+  if (triangulation.needsShift) {
+    // although only some of the triangles are crossing the dateline,
+    // all coordiantes need to be "shifted" to be positive
+    // to properly calculate the extent (and then possibly shifted back)
+
+    var sourceProjExtent = sourceProj.getExtent();
+    var sourceProjWidth = ol.extent.getWidth(sourceProjExtent);
     goog.array.forEach(triangulation.triangles, function(triangle, i, arr) {
       var src = triangle.source;
       ol.extent.extendCoordinate(extent,
-          [goog.math.modulo(src[0][0] + distance, distance), src[0][1]]);
+          [goog.math.modulo(src[0][0], sourceProjWidth), src[0][1]]);
       ol.extent.extendCoordinate(extent,
-          [goog.math.modulo(src[1][0] + distance, distance), src[1][1]]);
+          [goog.math.modulo(src[1][0], sourceProjWidth), src[1][1]]);
       ol.extent.extendCoordinate(extent,
-          [goog.math.modulo(src[2][0] + distance, distance), src[2][1]]);
+          [goog.math.modulo(src[2][0], sourceProjWidth), src[2][1]]);
     });
-    if (extent[0] > distance / 2) extent[0] -= distance;
-    if (extent[2] > distance / 2) extent[2] -= distance;
+
+    var right = sourceProjExtent[2];
+    if (extent[0] > right) extent[0] -= sourceProjWidth;
+    if (extent[2] > right) extent[2] -= sourceProjWidth;
   } else {
     goog.array.forEach(triangulation.triangles, function(triangle, i, arr) {
       var src = triangle.source;