// __stdcall means that the called function must clear the arguments from the stack before return
// __cdecl is the opposite, the caller function clears the stack
// its easier to use __stdcall now
void __stdcall CChat__Draw(void* this){
    
}

void __declspec(naked) HOOKCChat__Draw(){
    /*
    .text:1000EA60 000                 push    0FFFFFFFFh
    .text:1000EA62 004                 push    offset SEH_1000EA60
    .text:1000EA67 008                 mov     eax, large fs:0
    .text:1000EA6D 008                 push    eax
    */
    _asm {
        push ecx // ecx contains the this ptr for a __thiscall, save it on stack
        
        push ecx // push this ptr again on the stack, first parameter of CChat__Draw
        call CChat__Draw
        
        pop ecx // restore ecx register from stack
        
        // first two instructions replaced by the jump
        push 0xffffffff
        mov eax,vcmpaddr // push offset +0xEA60, need to recalculate
        add eax,0xBADFB
        
        // jump back
        mov eax,vcmpaddr
        add eax,0xEA67 // calculate return address, third instruction
        jmp eax
    }
}

hook:
MakeJump(vcmpaddr+0xea60, 7, HOOKCChat__Draw);