6 Replies Latest reply on Sep 2, 2010 12:08 AM by redditisgreat

    help aligning struct for sending array of structs to the GPU


      Hi there

      I have some structures, and I didn't understand how I should align them. 

      On the CPU I have an array of structures (voxel *VoxelList) and I want to send it to the GPU, where I copy the elements into another array which is on the GPU (GPUVoxelList). Then I want to access from the kernel each element with GPUVoxelList.


      here are the structures, organised as good as I could understand:




      typedef struct __attribute__ ((aligned(16))) Raza  


      cl_uint4 pozitie;    ->x

      cl_float4 directie;  ->x + 16

      cl_float dimensiune;  ->x + 32

      cl_float fov; ->x + 36

      cl_uchar4 mediu_parcurs; ->x + 40

      cl_uchar4 mediu_curent; ->x + 44

      cl_ushort2 pixel; ->x + 48

      cl_ushort influenta; ->x + 52

      cl_ushort luminozitate_curenta; ->x + 54

      cl_uchar padd[8]; ->x + 56

      }raza; ->x + 64

      typedef struct Material


      cl_uchar4 culoare; ->x

      cl_char4 normala; ->x + 4

      cl_uchar2 reflexivitate; ->x + 8

      cl_uchar2 transparenta; ->x + 12

      cl_ushort luminozitate; ->x + 16

      cl_uchar densitate; ->x + 18

      }material; ->x + 19

      typedef struct __attribute__ ((aligned(16))) Voxel 


      cl_uint fiu[8]; ->x

      cl_uint parinte; ->x + 32

      material m; ->x + 36

      cl_uchar padd[9]; ->x + 55

      }voxel; ->x + 64


      I am only sending the raza and the voxel structs. The material struct doesn't have to be padded because I padd at the end of the voxel struct and it starts at 36, right?


          • help aligning struct for sending array of structs to the GPU

            I compiled the code, and it doesn't work strangely I get only 0-s. Also changed the aligned(16) with packed.

            maybe because the array of structs on the device isn't aligned? How do I align a cl_mem? and the voxel structure where should start? at a multiple of 4? and the raza structure at a multiple of 16?

              • help aligning struct for sending array of structs to the GPU


                I hope these work: I've tested the 'raza' struct with the pixel field which seams ok, and the voxel struct with the 'parinte' field witch is 99% ok I assume the others are wrong because I did something wrong in the code, not because of the alignments.

                I think the idea was that material should start at a multiple of 16 (because it is aligned to 16) and the paddings help align parinte to 4 (uint=4) and the size of the structure to be multiple of 16 (64). Maybe this helps someone like me


                typedef struct Raza
                uint4 pozitie; //x, y, z
                float4 directie; //i, j, k (cu cat se misca la fiecare pas)
                float dimensiune; //cat de mare e cubul acum
                float fov; //cu cat creste la fiecare pas

                uchar4 mediu_parcurs; //r, g, b -> cat filtreaza din fiecare culoare

                uchar4 mediu_curent; //r, g, b, densitate

                uint pixel; //pixelul care trebuie updatat (w=pixel%width h=pixel/hidth)

                ushort influenta; //cat influenteaza culoarea lui pixelul
                ushort luminozitate_curenta; //luminozitatea mediului curent
                uchar padd[8];
                }__attribute__((aligned(16))) raza;



                typedef struct Material
                uchar4 culoare; //r, g, b ( [0, 255] )

                char4 normala; //x, y, z ( [-1, 1] * 127 )

                uchar2 reflexivitate; //indice reflexie, specularitate ( [0, 255] )
                uchar2 transparenta; //indice transparenta, specularitate ( [0, 255] )

                ushort luminozitate; //( [0, 65535] )

                uchar densitate; //( [0, 255] )
                }__attribute__((aligned(16))) material;

                typedef struct Voxel
                uint fiu[8];

                material m;
                uchar padd1[5];

                uint parinte;

                uchar padd2[4];
                }__attribute__((aligned(16))) voxel;


                and on the host:

                #pragma pack (push, 16)
                struct my_struct
                   ...same fields as the kernel source above...
                #pragma pack(pop)

                  • help aligning struct for sending array of structs to the GPU

                    Sorry for re-popping this thread... I ca't understand where the problem is:

                    the only member which seams not to work is densitate from material:

                    ( voxel.m.densitate, on the host it is anything, on the gpu it sais it is 255)

                    I also tried aligning the material struct to 8 and putting the padd[5] at the end of the material instead in the voxel struct.

                    Can you see any errors? 

                    the culoare, normala, and luminozitate from material are correct, and fiu and parinte from voxel, haven't tested the others. (they are correct for all members in the array, because there is an array of structs like this)

                    thank you