hi,
i will be passing timeGetTime values from CPU to a variable
in my shader and based on that possible seed value ,
I want to implement a random number generation function in HLSL , but actually currently have no idea about algorithms
As starting point what would you advise ?
And also what about producing something with same quality with rand() of C/C++ ,
is it a hard job or can it be done with a reasonable effort ?
many thanks in advance...
random number generation based on time in HLSL
Why would you want to do that in HLSL? That's not really HLSL's job, you should pass in those kind of parameters to the shader if you need them.
Author
Because I want to implement main `Update` method of my particle system
in GPU with vertex shaders ( since I am using D3D9 and i cant use geometry shaders ,i still have code in C++ side except `Update` part which is the meat of the job actually)
so that is why I want to have random number generation function in my shader
in current implementation , in CPU side update method of my particle system , I am already passing random numbers to the shader variables , but I want to keep CPU side as low as possible
in GPU with vertex shaders ( since I am using D3D9 and i cant use geometry shaders ,i still have code in C++ side except `Update` part which is the meat of the job actually)
so that is why I want to have random number generation function in my shader
in current implementation , in CPU side update method of my particle system , I am already passing random numbers to the shader variables , but I want to keep CPU side as low as possible
You might be able to leverage noise. Though that's not really suited for that purpose.
Any actually good random number generator is going to burn through too much instruction count to be of any good.
You can also write a bunch of random numbers to a texture and look that up in the shader. That's probably the best answer if you really want random numbers in your shader.
Any actually good random number generator is going to burn through too much instruction count to be of any good.
You can also write a bunch of random numbers to a texture and look that up in the shader. That's probably the best answer if you really want random numbers in your shader.
I guess this is what you're looking for =)
#define RANDOM_IA 16807#define RANDOM_IM 2147483647#define RANDOM_AM (1.0f/float(RANDOM_IM))#define RANDOM_IQ 127773#define RANDOM_IR 2836#define RANDOM_MASK 123459876int random_x;float random (){ int k; float ans; random_x ^= RANDOM_MASK; k = random_x / RANDOM_IQ; random_x = RANDOM_IA * (random_x - k * RANDOM_IQ ) - RANDOM_IR * k; if ( random_x < 0 ) random_x += RANDOM_IM; ans = RANDOM_AM * random_x; random_x ^= RANDOM_MASK; return ans;}float random ( float low, float high ){ float v = random(); return low * ( 1.0f - v ) + high * v;}float2 random ( float2 low, float2 high ){ float2 v = float2( random(), random() ); return low * ( 1.0f - v ) + high * v;}float3 random ( float3 low, float3 high ){ float3 v = float3( random(), random(), random() ); return low * ( 1.0f - v ) + high * v;}void seed ( int value ){ random_x = value; random();}
Author
glSmurf , thanks very much
yeah it seems as what i am looking for :)
just a quick question , by using shader model 1.1 2.0 and 4.0 , i could not compile it because of '^' operator , how can I resolve this issue ?
thanks in advance...
yeah it seems as what i am looking for :)
just a quick question , by using shader model 1.1 2.0 and 4.0 , i could not compile it because of '^' operator , how can I resolve this issue ?
thanks in advance...
From msdn:
"Bitwise operators are defined to operate only on int and uint data types. Attempting to use bitwise operators on float, or struct data types will result in an error."
Maybe you changed 'int random_x' to 'float random_x' ?
"Bitwise operators are defined to operate only on int and uint data types. Attempting to use bitwise operators on float, or struct data types will result in an error."
Maybe you changed 'int random_x' to 'float random_x' ?
@glSmurf: Can you please tell us exactly how you got your code to work (shader model, compile options) and in what context (pixel/vertex shader, software shader even ?) because I have some doubts: One thing I'm concerned is the bitwise operations (only available on SM >= 4), the other that your PRNG uses a global that gets changed. You can't do that with shaders IMHO.
First of all, it's not my own code. I got it from the NVidia DX10 SDK. I've used it in a vertex shader and it works just fine (shader model 4.0).
For more information check out the SDK.
File: ... / NVIDIA Direct3D SDK 10 / Source / Lightning / Lightning.fx
For more information check out the SDK.
File: ... / NVIDIA Direct3D SDK 10 / Source / Lightning / Lightning.fx
Thanks, that clarifies the problem: akhin uses DX9 so only SM 3 (or less) is available, unfortunately.
@akhin: Bear in mind that if you now go for a texture lookup in the vertex shader, this is not possible with SM 2.
@akhin: Bear in mind that if you now go for a texture lookup in the vertex shader, this is not possible with SM 2.
This topic is closed to new replies.
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