Two copies to store values

Question

I have this a piece of code, disassembled DX:

.text:004386D3                 push    ecx
.text:004386D4                 fld1
.text:004386D6                 fstp    [esp+26Ch+var_26C] ;load 1.0 value texture coords
.text:004386D9                 push    ecx
.text:004386DA                 fld1
.text:004386DC                 fstp    [esp+270h+var_270] ;load 1.0 value texture coords
.text:004386DF                 push    ecx
.text:004386E0                 fld     ds:__real@c1700000
.text:004386E6                 fstp    [esp+274h+var_274] ;load -15.0 value x vertex
.text:004386E9                 push    ecx
.text:004386EA                 fld     ds:__real@c1700000
.text:004386F0                 fstp    [esp+278h+var_278] ;load -15.0 value y vertex
.text:004386F3                 push    ecx
.text:004386F4                 fld     ds:__real@c1700000
.text:004386FA                 fstp    [esp+27Ch+var_27C] ;load -15.0 value z vertex
.text:004386FD                 lea     ecx, [ebp+var_22C] ;this pointer
.text:00438703                 call    j_D3DVERTEX__D3DVERTEX ;fills structure with values
.text:00438708                 mov     ecx, [ebp+var_8] ;var_8 pointer returned by Lock() buffer func
.text:0043870B                 mov     edx, [eax]
.text:0043870D                 mov     [ecx], edx
.text:0043870F                 mov     edx, [eax+4]
.text:00438712                 mov     [ecx+4], edx
.text:00438715                 mov     edx, [eax+8]
.text:00438718                 mov     [ecx+8], edx
.text:0043871B                 mov     edx, [eax+0Ch]
.text:0043871E                 mov     [ecx+0Ch], edx
.text:00438721                 mov     eax, [eax+10h]
.text:00438724                 mov     [ecx+10h], eax

This code fills one vertex structure with values:

-15.000000,-15.000000,-15.000000, 1.0,1.0

It seems values is stored into two copies. First copy of this values stored relatively ebp+var_22C and into ecx passed this pointer:

.text:004386FD                 lea     ecx, [ebp+var_22C] ; ecx has pointer this to store values
.text:00438703                 call    j_D3DVERTEX__D3DVERTEX ;fills structure with values

And second copy this values stored relatively ebp+var_8 after calling j_D3DVERTEX__D3DVERTEX:

.text:00438708                 mov     ecx, [ebp+var_8] ;var_8 pointer returned by Lock() buffer func

I.e. completely it's looks like:

.text:004386FD                 lea     ecx, [ebp+var_22C] ; ecx has pointer this to store values
.text:00438703                 call    j_D3DVERTEX__D3DVERTEX ;store values into structure
.text:00438708                 mov     ecx, [ebp+var_8] ;var_8 pointer returned by Lock() buffer func

If I right understood- why need two copy of this vertex values? Maybe it is important the vertex buffer created with D3DPOOL_MANAGED and D3DUSAGE_WRITEONLY parameters.

Answer 1

Inside D3DVERTEX__D3DVERTEX [ebp+var_334] i.e. ecx passed to variable [ebp+var_4] and in end of function [ebp+var_4] passed to eax as return:

.text:00439440 D3DVERTEX__D3DVERTEX proc near          ; CODE XREF: j_D3DVERTEX__D3DVERTEXj
.text:00439440
.text:00439440 var_5C          = dword ptr -5Ch
.text:00439440 var_58          = dword ptr -58h
.text:00439440 var_54          = dword ptr -54h
.text:00439440 var_4           = dword ptr -4
.text:00439440 arg_0           = dword ptr  8
.text:00439440 arg_4           = dword ptr  0Ch
.text:00439440 arg_8           = dword ptr  10h
.text:00439440 arg_C           = dword ptr  14h
.text:00439440 arg_10          = dword ptr  18h
.text:00439440
.text:00439440                 push    ebp
.text:00439441                 mov     ebp, esp
.text:00439443                 sub     esp, 44h
.text:00439446                 push    ebx
.text:00439447                 push    esi
.text:00439448                 push    edi
.text:00439449                 mov     [ebp+var_4], ecx

...........
.text:0043947B                 mov     eax, [ebp+var_4]
.text:0043947E                 pop     edi
.text:0043947F                 pop     esi
.text:00439480                 pop     ebx
.text:00439481                 mov     esp, ebp
.text:00439483                 pop     ebp
.text:00439484                 retn    14h
.text:00439484 D3DVERTEX__D3DVERTEX endp

and after D3DVERTEX__D3DVERTEX this eax used as base bointer to fill memory of vertex buffer with values:

.text:00438703                 call    j_D3DVERTEX__D3DVERTEX
.text:00438708                 mov     ecx, [ebp+var_8] ;pointer to vertex buffer
.text:0043870B                 mov     edx, [eax] ;eax returned by j_D3DVERTEX__D3DVERTEX

Maybe j_D3DVERTEX__D3DVERTEX used to arrange and prepare vertex values to fill vertex memory after calling j_D3DVERTEX__D3DVERTEX?