fix bug where last contour fill sometimes covered everything

this would only happen if its line rounded away to nothing,
because it only crossed the boundary an infinitesimal amount

Author: alexcjohnson

src/traces/contour/find_all_paths.js

@@ -84,13 +84,15 @@ function makePath(pi, loc, edgeflag) {
         if(equalPts(pts[pts.length - 1], pts[pts.length - 2])) pts.pop();
         locStr = loc.join(',');
 
+        var atEdge = (marchStep[0] && (loc[0] < 0 || loc[0] > n - 2)) ||
+                (marchStep[1] && (loc[1] < 0 || loc[1] > m - 2)),
+            closedLoop = (locStr === startLocStr) && (marchStep.join(',') === startStepStr);
+
+        if(atEdge) pi.foundedge = true;
+
         // have we completed a loop, or reached an edge?
-        if((locStr === startLocStr && marchStep.join(',') === startStepStr) ||
-            (edgeflag && (
-                (marchStep[0] && (loc[0] < 0 || loc[0] > n - 2)) ||
-                (marchStep[1] && (loc[1] < 0 || loc[1] > m - 2))))) {
-            break;
-        }
+        if((closedLoop) || (edgeflag && atEdge)) break;
+
         mi = pi.crossings[locStr];
     }
 

src/traces/contour/plot.js

@@ -93,6 +93,8 @@ function emptyPathinfo(contours, plotinfo, cd0) {
             // all unclosed paths (may have less items than starts,
             // if a path is closed by rounding)
             edgepaths: [],
+            // we found some edges (even if they later got removed due to rounding)
+            foundedge: false,
             // all closed paths
             paths: [],
             // store axes so we can convert to px
@@ -163,7 +165,7 @@ function makeFills(plotgroup, pathinfo, perimeter, contours) {
 }
 
 function joinAllPaths(pi, perimeter) {
-    var fullpath = (pi.edgepaths.length || pi.z[0][0] < pi.level) ?
+    var fullpath = (pi.foundedge || pi.z[0][0] < pi.level) ?
             '' : ('M' + perimeter.join('L') + 'Z'),
         i = 0,
         startsleft = pi.edgepaths.map(function(v, i) { return i; }),

src/traces/contour/style.js

@@ -42,13 +42,18 @@ module.exports = function style(gd) {
                     line.dash);
         });
 
-        c.selectAll('g.contourbg path')
-            .style('fill', colorMap(start - cs / 2));
+        var firstFill;
 
         c.selectAll('g.contourfill path')
-            .style('fill', function(d, i) {
-                return colorMap(start + (i + 0.5) * cs);
+            .style('fill', function(d) {
+                if(firstFill === undefined) firstFill = d.level;
+                return colorMap(d.level + 0.5 * cs);
             });
+
+        if(firstFill === undefined) firstFill = start;
+
+        c.selectAll('g.contourbg path')
+            .style('fill', colorMap(firstFill - 0.5 * cs));
     });
 
     heatmapStyle(gd);