[GitHub] 100pah commented on issue #9171: fix #8009 & #5969, symbol symbolSize and opacity setting for category itemStyle in graph

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100pah commented on issue #9171: fix #8009 & #5969, symbol symbolSize and opacity setting for category itemStyle in graph
URL: https://github.com/apache/incubator-echarts/pull/9171#issuecomment-432201790
 
 
   It is a little complicated about this issue.
   First of all, there is a "programming contract" about when and how to use the properies in option to render a chart in echarts:
   
   Tow cases: 
   
   **(A)** 
   Basically, properties are retrieved from model (essentially, from "option" in model) directly when rendering in xxxView.
   The model cascade mechanism ensure that get the right property.
   The "cascade" means, for example: 
   + itemModel - seriesModel (by default)
   + itemModel - categoryModel - seriesModel (in graph)
   + itemModel - levelModel - seriesModel (in tree, treemap, ...）
   + ... (other cases)
   
   **(B)** 
   If a properties is available to be modified by other components (e.g., `legend`, `visualMap`), 
   it will be retrieved in the "visual encoding stage", and be saved to data 
   (by `data.setVisual() / data.setItemVisual()`). When chart is finally being rendered in xxxView, it will 
   be retrieved from data (by `data.getItemVisual()`). 
   
   ---
   
   The "contract" is a little complicated and a little fuzzy. Why not just 
   trace them all via `data.set/getItemVisual`? I think there is two reasons: 
   (1) A chart needs many properties. If we retrieve them all and save to `data` and finally retrieve from `data` and 
   then render, it brings some redundancy of logic and code.
   (2) Save obj by the unit of `data item` probably cause performance issue (mainly, GC issue) in large data. 
   
   ---
   
   
   In this case, we have these properties to be considered:
   `color`, `opacity`, `symbolSize`, `symbol`, `symbolOffset`, `symbolRotate`, `symbolKeepAspect`.
   
   Probably we have to trade them in different way: 
   
   (1) Follow to the contract (B) above:
   `color` (implemented)
   `opacity` (not implemented yet, can be implemented in `categoryVisual` like this PR did.）
   `symbolSize` (not implemented yet, can be implemented in `categoryVisual` like this PR did.)
   
   (2) Follow to the contract (A) above:
   `symbolOffset` (implemented)
   `symbolRotate` (implemented)
   `symbol` (not implemented yet)
   
   (3) 
   `symbolKeepAspect` (?)
   I am not sure about this property. Currently it has been implemented follow the (A), but
   probably it should not be able to modified by other components I think. What your opinion on it ?
   @Ovilia 

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