Assembly code snippets

Details

Title	Angle from delta values
Author	Thomas
Submitted by:	Thomas
Date added:	2002-02-18 15:57:14
Date modified:	2002-02-18 15:57:14

Comments

This proc takes the horizontal and vertical delta values of two points and returns the angle between them in tenths of degrees (range 0-3599). I just converted some C example I found on the web (didn't mention the original author).
Coordinates and angles are defined like this:
positive Y: up, negative Y: down, positive X: right, negative X: left. Angles: up: 0, right: 900, down 1800, left 2700.

Snippet

; Converts horizontal and vertical delta values into
; tenths of degrees (range 0-3599).
; Converted from C example by unkown author.
DeltaToAngle    proc deltaX:DWORD, deltaY:DWORD
LOCAL   temp:DWORD
    .data
    dta_rangeval_000    REAL4 1800.0
    .code
    mov     ecx, deltaX
    mov     edx, deltaY

    or      edx, edx
    jnz     @dta1
    mov     eax, 900
    cmp     ecx, 0
    jg      @F
    mov     eax, 2700
    @@:
    ret
    @dta1:
    xor     eax, eax
    or      ecx, ecx
    jnz     @dta2
    cmp     edx, eax
    jg      @F
    mov     eax, 1800
    @@:
    ret
    ret
    @dta2:

    finit

    fild    deltaY
    fild    deltaX

    fpatan                      ;ST(0)=angle in radians
    fldpi                       ;ST(1)=angle in radians, ST(0)=pi
    fdivp   ST(1),ST(0)         ;ST(0)=angle/pi
    fmul    dta_rangeval_000    ;ST(0)=(angle/pi) * 1800 = angle in degrees (*10)
    fistp   temp                ;temp=ST(0)=angle in degrees (*10)

    mov     eax, 900
    sub     eax, temp

    @@:
    cmp     eax, 0
    jge     @F
    add     eax, 3600
    jmp     @B
    @@:

    @@:
    cmp     eax, 3600
    jle     @F
    sub     eax, 3600
    jmp     @B
    @@:
ret
DeltaToAngle    endp