Set color conditional

[ggetz]

Added support for color conditionals. They are in the form:

color : {
   conditional : {
      'booleanExpression1` : `colorExpression1',
      'booleanExpression2` : `colorExpression2',
     // etc...
   },
   default : `defaultColorExpression`
}

We check each condition in order, and, if true, evaluate the corresponding color expression.

I added the file ColorConditional.js for the conditionals. It has both an evaluate(feature) and evaluate(feature, result)` function. I think we may only need the latter?

I deleted ColorMapExpression and ColorRampExpression.

I added tests for ColorConditional and for Cesium3DTileStyle and Cesium3DTileset to check if the style is properly applied.

I also updated the Sandcastle example.

I'm having trouble with the Change Style Using ID and Change Style Using Height buttons, because they generate the conditionals depending on the number of colors, and I was having trouble making the conditional JSON expression, because the Boolean expressions have to be strings: (ex. '${height} < 1' : 'color("red")' not ${height < 1 : 'color("red")'). So that part of the Sandcastle example has not yet been updated.

[pjcozzi]

I think we may only need the latter?

I think we need both. We should probably position this as a general "conditional", not specific to colors even if that is where the original use case came from.

[ggetz]

I think we need both. We should probably position this as a general "conditional", not specific to colors even if that is where the original use case came from.

OK, that should be pretty easy, Should I do that in this PR?

[pjcozzi]

Should I do that in this PR?

Yes, let me know if you run into any ideas. I will also do the spec/schema for this tomorrow or Friday.

[pjcozzi]

I was having trouble making the conditional JSON expression, because the Boolean expressions have to be strings

What exactly is the problem? Can't we just generate strings?

[ggetz]

I set up the conditional like this:

var conditional  = {};

Then set up the conditional and color expression strings and use

conditional[conditionalExpression] = colorExpression;

but this outputs { ${height} < 1 : 'color("red")' } not { '${height < 1' : 'color("red")' }. Is there a way to make the "attribute" a string?

[pjcozzi]

I would actually remove this for now until we expose the AST (probably not for the first pull request into 3d-tiles).

Otherwise, this looks like a fast get/set, but it is just as bad as assigning a new style since it forces a recompile.

[pjcozzi]

Looks good, just those comments.

[pjcozzi]

but this outputs { ${height} < 1 : 'color("red")' } not { '${height < 1' : 'color("red")' }. Is there a way to make the "attribute" a string?

I still don't understand; is this with JSON.stringify? The conditional is a string containing strings. Is there an issue escaping them?

[ggetz]

I still don't understand; is this with JSON.stringify? The conditional is a string containing strings. Is there an issue escaping them?

I didn't use JSON.stringify- I will try it with that.

[ggetz]

I think we need both. We should probably position this as a general "conditional", not specific to colors even if that is where the original use case came from.

The default default value is currently the expression color("#ffffff"). Should we not have a default default value since we don't know what type this is supposed to evaluate to since it's being used in a general sense?

[pjcozzi]

Let's remove default from the schema completely since a conditional that is just 'true' at the end is the same thing.

[ggetz]

In the case that someone doesn't provide a 'true' condition, it will evaluate the expressions for any features that don't fall into the other conditionals as undefined. Is that behavior we want?

[pjcozzi]

Is that behavior we want?

Yes.

[ggetz]

OK, I updated the name of the file to ExpressionConditional instead of ColorConditional, removed the default property, updated the tests, and updated the sandcastle example.

[pjcozzi]

Looks great, just one rename request: throughout, rename ExpressionConditional to ConditionalExpression.

[ggetz]

Updated.

[pjcozzi]

👍