Jump to content
  • Advertisement
Sign in to follow this  
Giallanon

DX11 HLSL matrix, colum major

This topic is 1589 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

There's something I don't understand with the way DX11 HLSL parse a constant buffer when it's time to "transform it" in a matrix.
I've declared a constant buffer like this:
 

cbuffer cbPerMesh : register( b1 )
{
   matrix<float,3,4> World;
}

 
The shader is compiled with D3DCOMPILE_PACK_MATRIX_COLUMN_MAJOR.
 
The shader expects to receive matrix in a colum major form, but it's not working as I supposed to.
I'm feeding the shader with this data:
 

f32 temp[12] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
gpuProg.updateConstantBuffer (hCBPerMesh, &temp, sizeof(f32) * 12);

 
To my understanding, the World matrix should be like this:

1 2 3 4
5 6 7 8
9 10 11 12

 ie: 3 rows, 4 columns per row, feeded by an array of 12 floats.

 
By debugging the shader, I'm able to see the following:

Data buffer:
#,Indirizzo,Float4
0,[0x00000000-0x0000000F],{+1, +2, +3, +4}
1,[0x00000010-0x0000001F],{+5, +6, +7, +8}
2,[0x00000020-0x0000002F],{+9, +10, +11, +12}

which is right, and means that I'm transferring the buffer correctly.
 

 

What I don't understand, is that the World matrix, inside the vertex shader, appears like this:
 

World[0] x = 1.000000000, y = 5.000000000, z = 9.000000000, w = 0.000000000 float4
World[1] x = 2.000000000, y = 6.000000000, z = 10.000000000, w = 0.000000000 float4
World[2] x = 3.000000000, y = 7.000000000, z = 11.000000000, w = 8.660300000 float4


I see 2 "errors":
First, my buffer is not taken as a colum major, otherwise World[0] should be like "1, 2, 3, 4"
Second, where are my "4", "8" and "12" left? They are skipped when the compiler parse the buffer into the matrix.
 
 
To fix this, I have to transpose() my buffer, and then declare

row_major float3x4 World;

This way everything works as expected

Share this post


Link to post
Share on other sites
Advertisement
Thank you. After years of working with row major, I've some trouble figuring the Real Memory layout of a column major Matrix. It makes sense, a column of 3 floats it's represented as a 4float register inside hlsl. That explains everything.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!