fix one-sided + set width violin axis-expand case

Author: etpinard

Diff for: src/traces/box/cross_trace_calc.js

@@ -128,12 +128,12 @@ function setPositionOffset(traceType, gd, boxList, posAxis) {
         var edgeminus;
 
         if(side === 'positive') {
-            pushplus = dPos / 2;
+            pushplus = dPos * (width ? 1 : 0.5);
             edgeplus = edge;
             pushminus = edgeplus = bPos;
         } else if(side === 'negative') {
             pushplus = edgeplus = bPos;
-            pushminus = dPos / 2;
+            pushminus = dPos * (width ? 1 : 0.5);
             edgeminus = edge;
         } else {
             pushplus = pushminus = dPos;
@@ -193,7 +193,6 @@ function setPositionOffset(traceType, gd, boxList, posAxis) {
                 // (<-) fallback to push value
                 vpadminus = pushminus;
             }
-
         } else {
             vpadplus = pushplus;
             vpadminus = pushminus;

Diff for: test/image/baselines/violin_box_multiple_widths.png

@@ -34,10 +34,25 @@
             "fillcolor": "#c78dd3",
             "opacity": 0.6,
             "y0": 0.2
+        }, {
+            "type": "violin",
+            "width": 0.4,
+            "name": "width: 0.4 (solo)",
+            "x": [0, 5, 7, 8],
+            "side": "positive",
+            "line": {
+                "color": "black"
+            },
+            "fillcolor": "#8dd3c7",
+            "opacity": 0.6,
+            "y0": 0.0,
+            "xaxis": "x2",
+            "yaxis": "y2"
     }],
     "layout": {
-        "title": "Violins/boxes - with multiple widths",
-        "legend": {"x": 0},
+        "grid": {"rows": 1, "columns": 2, "pattern": "independent"},
+        "title": {"text" :"Violins/boxes - with multiple widths", "x": 0, "xref": "paper"},
+        "legend": {"x": 1, "y": 1, "xanchor": "right", "yanchor": "bottom"},
         "xaxis": {"zeroline": false},
         "yaxis": {"dtick": 0.1, "gridcolor": "black"}
     }