I'm doing a function in responce to WM_MOUSEMOVE to move my camera in opengl application.
The function is to take the STARTING POINT (old lParam from the wm_lbuttondown command)and subtract CURRENT POINT from STARTING POINT, and multiply the result by some floating point coefficient.
class cam
{
int sp; //staring point saved here
float x_coeff;//the addresses of sp and x_coeff are aligned , I can load them both as a quad-word later
}
case WM_LBUTTONDOWN:
cam.sp=lParam;
return 0;
case WM_MOUSEMOVE:
cam.drag_camera(lParam);
return 0;
cam::drag_camera(LPARAM lParam)
{
float step=0.001;
short old_x=sp&0xFFFF;
short old_y=sp>>16;
short current_x=lParam&0xFFFF;
short curretn_y=lParam>>16;
x_move=(old_x-current_x)*step;
.... do something with the step
}
Ok, it works, but I'm trying to practice in using asm and all those nice registers. So here is my code for the same thing but using mmx registers
cam::drag_camera(LPARAM lParam)
{
_asm
{
movd mm0,lParam //MOVE current mouse LPARAM point to mm0 - mm0 = 00:00:cy:cx
movq mm1,[ebx+40h] //MOVE starting mouse point LPARAM to low dword of mm1 and x_coeff in high dword of mm1 - mm1 = x_coeff:sy:sx
psubw mm1,mm0 //SUB current - starting mm1 = x_coeff:(sy-cy):(sx-cx)
punpcklwd mm2,mm1 //PUT packed word result to mm2 double words m2=00:(sy-cy):00:(sx-cx)
psrad mm2,16 //Sign extend both double words of the result m2=(sy-cy):(sx-cx)
cvtpi2ps xmm7,mm2 //MOVE X Y result to XMM7 xmm7 = 0000:0000:sy-cy:sx-cx
psrlq mm1,32 //SHIFT the x_coeff from the high dword to the left m1=00:00:x_coeff
movq2dq xmm6,mm1 //SEND coeff to xmm6 low dword xmm6=0000:0000:0000:x_coeff
shufps xmm6,xmm6,00h //SHUFFLE x_coeff everywhere xmm6=x_coeff:x_coeff:x_coeff:x_coeff
mulps xmm7,xmm6 //MULTIPLY 0:0:Y:X by x_coeff xmm7=0000:0000:(sy-cy)*x_coeff:(sx-cx)*x_coeff
}
}
The question is - is this a quick method of doing such a simple athirmetic or I could choose some other way of doing those things? Thanks
