[GitHub] [echarts] jiawulin001 commented on a diff in pull request #16895: fix: all data mapped to one col when zooming in

[GitBox]

jiawulin001 commented on code in PR #16895:
URL: https://github.com/apache/echarts/pull/16895#discussion_r851597412


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src/scale/helper.ts:
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@@ -128,7 +128,12 @@ export function contain(val: number, extent: [number, 
number]): boolean {
 
 export function normalize(val: number, extent: [number, number]): number {
     if (extent[1] === extent[0]) {
-        return 0.5;
+        if (val !== extent[0]) {

Review Comment:
   My apologies I didn't explain enough in the PR and comment. Let me show you 
the dataflow and then the strategy would be clear.
   First, we are zooming in to 'b' category and only 'b' at this chart:
   <img width="437" alt="before#16746" 
src="https://user-images.githubusercontent.com/14244944/163664209-7654625a-2349-41dd-9eea-9531553b9d92.png";>
   Then Echarts tries to determine the location of 'a', 'b' and 'c' column in 
the chart **AFTER ZOOMING**. So the `extent` here is `[1, 1]`:
   
https://github.com/apache/echarts/blob/a5257e38ad7776c766879c83854b1faa2771a454/src/coord/Axis.ts#L122-L133
   At line 125, we enter function `normalize` which returns the **relative 
location** (0~1) of the column according to their location **BEFORE ZOOMING** 
(which is 0, 1, 2 for 'a', 'b', 'c' respectively):
   
https://github.com/apache/echarts/blob/a5257e38ad7776c766879c83854b1faa2771a454/src/scale/helper.ts#L129-L132
   At this moment, remember that `extent` is `[1, 1]`, so no matter what `data` 
is, function `normalize` returns 0.5, which means all the three columns are 
located at the middle of the chart after zooming. 
   To solve this, I add a judgement: `if (val !== extent[0])` which checks 
whether the column is the one we are zooming in at. If it's not, then we return 
a correct relative location of the column. Here for 'a', 'b', 'c', they are 0, 
1, 2 before zooming and then -0.5, 0.5, 1.5 (locate at -50%, 50%, 150%) after 
zooming. 
   
![before#16746](https://user-images.githubusercontent.com/14244944/163665200-004e2945-c010-4332-a7fe-a22c8504951c.png)
   
   Also, another bug is preventing me to distinguish the three columns. At line 
132 we enters function `linearMap`, `subRange` is 0 because r0 = r1 = 320, 
which result in `return (val - d0) / subDomain * subRange + r0` equaling r0 no 
matter what `val` is. That means all three columns still locate at 320 (0.5 * 
640).
   
https://github.com/apache/echarts/blob/a5257e38ad7776c766879c83854b1faa2771a454/src/util/number.ts#L47-L100
   To solve this, I add a check whether `subRange` is 0 and if yes then just 
return `val * 2 * r0`. When `subRange` is 0, `r0` is exactly half length of the 
chart, 0.5*640 = 320. So `val * 2 * r0` = val * chartLength would be the 
absolute location of corresponding relative location.
   
   



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