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Variable index

Started by bdubreuil Jan 16, 2012 at 12:33 AM 2 replies 2.7k views

Original Post

Jan 16, 2012 at 12:33 AM

Hi,

I am a beginner with hlsl and I'd like to know if you actually can do something like this, which is setting a global variable's index with another global scalar variable:


 int t = 5;
 float g[t];

If you can't do something like this in hlsl, then can you change the array to a greater or lower number through xna?

Thank you

Thecheeselover

ViperG

Jan 16, 2012 at 1:26 AM

You can do something like this:

#define Global 5;

float g[Global];
int t = Global;
int z = Global;

MJP

Jan 16, 2012 at 4:59 AM

Arrays in HLSL need to have a length that is static at compile time. So in other words..


 // You can do this...
 static const uint ArraySize = 5
 float Array[ArraySize];
 
 // Or you can do this...
 #define ArraySize 5
 float Array[ArraySize];
 
 // But you can't do this
 uint ArraySize = 5; 
 float Array[ArraySize];

Usually what you do, is you define the array to some maximum size and then set another variable to a value representing how many values to actually use from the array. Like this:


 static const uint MaxValues = 5;
 float Values[MaxValues];
 uint NumValuesToUse;

Just be careful...depending on the shader profile you use the compiler's ability to represent loops in shader assembly may be limited.

bdubreuil

Jan 16, 2012 at 12:51 PM

Thank you both!

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