3D Tiles - ternary functions

[lilleyse]

@Dylan-Brown

Before getting into vector math, there are two more functions to handle. You'll need to add TERNARY to ExpressionNodeType.js. Handling three operators will be similar to here: #4688 except you'll use left, right, and test. The x values below can be passed as the test argument for new Node.

clamp(x, minVal, maxVal) - use CesiumMath.clamp
mix(minVal, maxVal, x) - use CesiumMath.lerp

Even though this is just two functions, use the data-driven approach like before so it is easy to add others.

[Dylan-Brown]

@lilleyse
Sounds good! I'll get working on it.
Also, I noticed in Math.js, where CesiumMath is defined, the grammar in the comment above the definition of clamp is wrong. It says "Constraint a value" where it should be "Constraints a value." Should I fix this in my PR, or should I do it separately in a PR to master, or what?
Also, should I call the function lerp or should I call it mix?

[Dylan-Brown]

Also, here's something else:

CesiumMath.clamp = function(value, min, max)
CesiumMath.lerp = function(p, q, time)

Applying left, right, and test to them using a data driven approach doesn't make sense, since I'm assuming

• for clamp, left=min, right=max, and test=value
• for lerp, left=p, right=q, test = time

and to use a data driven approach, I would write something like

if (defined(ternaryFunctions[value])) {
    return value + '(' + left + ', ' + right + ', ' + test + ')';
}

and so the definitions of the functions, specifically, the ordering of the arguments, doesn't quite work out

[lilleyse]

Should I fix this in my PR, or should I do it separately in a PR to master, or what?

You can do it in this PR

Also, should I call the function lerp or should I call it mix?

We tend to side with the glsl naming, so go with mix.

and so the definitions of the functions, specifically, the ordering of the arguments, doesn't quite work out

Yeah true... I'd be ok if the 1st and 2nd params go to left and right while the 3rd goes to test, regardless of the meaning of the parameters.

[Dylan-Brown]

@lilleyse
I believe this is done, unless there's other work for the ternary functions!

[pjcozzi]

@lilleyse OK to close this?