Jump to content

  • Log In with Google      Sign In   
  • Create Account

Banner advertising on our site currently available from just $5!


1. Learn about the promo. 2. Sign up for GDNet+. 3. Set up your advert!


f16tof32 f32tof16 doesn't work correctly


Old topic!
Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

  • You cannot reply to this topic
7 replies to this topic

#1 zhugel   Members   -  Reputation: 118

Like
0Likes
Like

Posted 19 July 2013 - 07:14 PM

Hi,

 

I am trying to read&modify the data from my vertex buffer in the compute shader. the position in the vertex buffer has the format of R16G16B16A16. (there are some other elements in the vertex buffer as well: normal, color, texcoord...)

 

here is the compute shader code to read&write the position value.

 

uint nOffsetPosXY = vDispatchThreadId.x*nStride;
uint nOffsetPosZW = nOffsetPosXY + 4;
uint nXY = gVertexBufferSrcSRV.Load(nOffsetPosXY);
uint nZW = gVertexBufferSrcSRV.Load(nOffsetPosZW);
float4 vInPos;
vInPos.x = f16tof32(nXY);
vInPos.y = f16tof32(nXY>>16);
vInPos.z = f16tof32(nZW);
vInPos.w = f16tof32(nZW>>16);
 
// some modification for the position
vInPos.z = 10; // value doesn't behave correctly
 
// write into another UAV buffer
uint nXYNew = f32tof16(vInPos.x)|(f32tof16(vInPos.y)<<16);
uint nZWNew = f32tof16(vInPos.z)|(f32tof16(vInPos.w)<<16);
gVertexBufferDSTUAV.Store(nOffsetPosXY, nXYNew);
gVertexBufferDSTUAV.Store(nOffsetPosZW, nZWNew);
 
I am sure the offset is correct since if i set x,y,z individually to 0, i can see the value in the corresponding axis is set to 0 visually. but if i set the value other than 0, the value doesn't behave correctly. (although the sign is correct.)
 
My feeling is that the f16tof32 f32tof16 doesn't work correctly. (or maybe i did something stupid. tongue.png )
 
Any help or suggestion would be really appreciated. 
 
By the way, i couldn't find any tool to debug compute shader on PC, PIX & VS2012 graphics debugger don't work. Is there any good tool for debugging the compute shader?
 
Thanks!!!

 


Edited by MJP, 19 July 2013 - 11:08 PM.


Sponsor:

#2 Muzzy A   Members   -  Reputation: 733

Like
0Likes
Like

Posted 19 July 2013 - 09:31 PM

I've never used f32tof16... but I know you can't shift a float or at least if you do you completely mess it up, you wont get the result you were expecting. Unless there's some support for it in shaders that I didn't know of.

 

Binary operators weren't meant for floats

 

I would look up on binary operators if I were you. 1 << 8 will give you 256, but 1.0f << 8 ( assuming it compiles ) will give you something MUCH different.

 

The same goes for every other operator, 2 | 3  gives you 3: 2.0f | 3.0f gives you god only knows what.

 

 

 

and i would say the only reason why it works when you give it 0 is because 0 << anything is always 0.


Edited by Muzzy A, 19 July 2013 - 10:04 PM.


#3 zhugel   Members   -  Reputation: 118

Like
0Likes
Like

Posted 19 July 2013 - 10:25 PM

f32tof16 Converts an input into a float16 type, and the return value is uint: 

uint f32tof16(in  float value);

http://msdn.microsoft.com/en-us/library/windows/desktop/ff471399(v=vs.85).aspx

The shifting is to pack 2 int16s into 1 int32.



#4 Muzzy A   Members   -  Reputation: 733

Like
0Likes
Like

Posted 19 July 2013 - 10:28 PM

Then that function name is misleading, 'f32' to 'f16'.

 

 

 

I just wanted to do this to make it more readable :)

 


uint nOffsetPosXY = vDispatchThreadId.x*nStride;
uint nOffsetPosZW = nOffsetPosXY + 4;
uint nXY = gVertexBufferSrcSRV.Load(nOffsetPosXY);
uint nZW = gVertexBufferSrcSRV.Load(nOffsetPosZW);
float4 vInPos;
vInPos.x = f16tof32(nXY);
vInPos.y = f16tof32(nXY>>16);
vInPos.z = f16tof32(nZW);
vInPos.w = f16tof32(nZW>>16);
 
// some modification for the position
vInPos.z = 10; // value doesn't behave correctly
 
// write into another UAV buffer

uint nXYNew = f32tof16(vInPos.x)|(f32tof16(vInPos.y)<<16);
uint nZWNew = f32tof16(vInPos.z)|(f32tof16(vInPos.w)<<16);
gVertexBufferDSTUAV.Store(nOffsetPosXY, nXYNew);
gVertexBufferDSTUAV.Store(nOffsetPosZW, nZWNew);




Edited by Muzzy A, 19 July 2013 - 10:38 PM.


#5 MJP   Moderators   -  Reputation: 13111

Like
1Likes
Like

Posted 19 July 2013 - 11:12 PM

Are you using DXGI_FORMAT_R16G16B16A16_FLOAT for the position element in your vertex buffer? You said the format is R16G16B16A16, but there are several varieties of that format.

For debugging compute shaders the only tools you can use are Nsight (Nvidia) and GPU PerfStudio (AMD). However you don't necessarily need any tools to debug this...you can copy your buffer to a staging buffer that you can MAP on the CPU so that you can print out the values or inspect them in a debugger.


Edited by MJP, 19 July 2013 - 11:13 PM.


#6 Matias Goldberg   Crossbones+   -  Reputation: 4407

Like
0Likes
Like

Posted 19 July 2013 - 11:55 PM

Without taking an in-depth look, I spotted these two:
vInPos.x = f16tof32(nXY);
vInPos.z = f16tof32(nZW);
Which could be wrong. They could be:
vInPos.x = f16tof32(nXY & 0x0000ffff);
vInPos.z = f16tof32(nZW & 0x0000ffff);
You should also check that nStride is correct, and that vDispatchThreadId.x*nStride actually results in what you expect it to be.

#7 zhugel   Members   -  Reputation: 118

Like
0Likes
Like

Posted 20 July 2013 - 08:39 AM

Thanks a lot guys for the relies! smile.png

Muzzy: Thx for cleaning up the code, it is much more readable. smile.png yeah, i agree, the name is a bit misleading.

MJP: Yes, i am using DXGI_FORMAT_R16G16B16A16_FLOAT. Ok, i will give Nsight a try, thx for the suggestion. smile.png Yes, i could map the buffer, but it would be much easier if i could debug the shader directly, even with assembly. ;) I did similar things as you suggested: draw the mesh later and using pix to inspect the vertex buffer, i can see the result is wrong but not sure which step is causing problem. it would be nice to be able to debug step by step. 

Matias: according to the document, f16tof32 Converts the float16 stored in the low-half of the uint to a float. so should be fine. I've indeed tried the one with &0x0000ffff, still the same result. 

to remove the dependency of nStride, i've set the numthreads to [1,1,1] with dispatch(1,1,1), so vDispatchThreadId.x would be always 0, and only the first vertex is touched. so i think the nStride is not the problem. 


Edited by zhugel, 20 July 2013 - 08:49 AM.


#8 zhugel   Members   -  Reputation: 118

Like
1Likes
Like

Posted 20 July 2013 - 02:08 PM

MJP: Actually, you are right! the problem is because the vertex position format is DXGI_FORMAT_R16G16B16A16_SNORM! 

 

So any value outside of the range of [-1, 1] would not work.


Edited by zhugel, 20 July 2013 - 02:28 PM.





Old topic!
Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.



PARTNERS