Is a static const initialized once or everytime?

uniform float var1;
uniform float var2;
static const float varSum = var1 + var2;

What happens to varSum in this situation?

 

There are three possibilities I can think of:

A) The shader compiler throws an error
B) The shader compiler sets varSum to 0.0
C) The shader compiler ignores the static const and ... magic happens?

Option A would be the most correct in my opinion. Since var1 & var2 don't exist at compile time, there's no way for the value to actually be const. A static const variable should mean it is known at compile time and cannot be changed by the shader.

Option B would be a semi-logical option as var1 and var2 could be considered 0 at compile time. It'd be wrong, but I can see some compiler making this choice.

Option C would mean the compiler sees that you're not using const values as inputs, and just ignores the modifiers you've set and magically turn that line into a macro that just puts (var1 + var2) into your shader whenever you use varSum. This is highly unlikely ... but I wouldn't put it past some shader compiler to do some bullshi...uh bullish magic like that.

 

I think its something like the option c with unity, it does compile and value is correctly set to the sum of uniforms. Probably ignores the static and const or just reinitializes the variable everytime, i dont know.

 

Well, it's the default Microsoft shader compiler likely doing this. I want to try this now and look at the compiled shader because that really shouldn't work.

 

my compiled shader says:

and Microsoft says:

So, it shouldnt work but it does. very strange.