[GitHub] [incubator-echarts] 100pah commented on a change in pull request #11684: WIP(axisPointer): snapping logic WIP.

[GitBox <gi...@apache.org>]

100pah commented on a change in pull request #11684: WIP(axisPointer): snapping logic WIP.
URL: https://github.com/apache/incubator-echarts/pull/11684#discussion_r350717249
 
 

 ##########
 File path: src/component/axisPointer/axisTrigger.js
 ##########
 @@ -97,19 +97,92 @@ export default function (payload, ecModel, api) {
 
     // Process for triggered axes.
     each(coordSysAxesInfo.coordSysMap, function (coordSys, coordSysKey) {
+        /**
+         * If both x and y axes are snapping and one and only one of them is
+         * of category type, then the category axis is used as primary
+         * snapping, otherwise the baseAxis is used as primary snapping.
+         * The snapped value of the other axis is calculated from it.
+         *
+         *  4 |                 *
+         *  3 |       *
+         *  2 |            *
+         *  1 |  *     +
+         *    ---------------------
+         *       a    b    c    d
+         *
+         * In the above example, the x axis is in category type, and y axis
+         *     value.
+         * The *'s are data items, + is the mouse position.
+         *
+         * If both x and y axes are using snapping, then:
+         * 1. x axis is used as primary snapping axis because it's the only
+         *     category axis.
+         * 2. The nearest x value to the mouse is 'b', so 'b' is used as
+         *     snapped x value.
+         * 3. The corresponding y value of 'b' is 3, so 3 is used as snapped y
+         *     value.
+         * 4. So the axisPointer should be at ('b', 3).
+         *
+         * If only x is snapping, then the axisPointer should be at ('b', 1).
+         * If only y is snapping, then the axisPointer should be at the
+         *     position of +.
+         */
+
         // If a point given, it must be contained by the coordinate system.
         var coordSysContainsPoint = isIllegalPoint || coordSys.containPoint(point);
 
+        var snapXor; // One and only one of the axes is snapping
+        var snapBoth = true; // Both axes are snapping
+        var primarySnapAxis;
+        each(coordSysAxesInfo.coordSysAxesInfo[coordSysKey], function (axisInfo) {
+            if (snapXor === undefined) {
+                snapXor = axisInfo.snap;
+            }
+            else {
+                snapXor = snapXor && !axisInfo.snap || !snapXor && axisInfo.snap;
+            }
+            snapBoth = snapBoth && axisInfo.snap;
+            axisInfo.snap && (primarySnapAxis = axisInfo.axis);
+        });
+
+        if (!snapBoth && !snapXor) {
+            // Snap none
+            return;
+        }
+
+        if (!snapXor) {
+            // Snap both
+            var coord = coordSys.getCartesians()[0];
 
 Review comment:
   Might no cartesian coord sys. e.g., only polar?

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