; ==============================================================================
; EBLAN ENGINE - Math, Fixed-Point Trigonometry & RNG
; ==============================================================================

.data
fAngleDiv       REAL4 256.0
fFixedScale     REAL4 65536.0
fScreenHalfW    REAL4 160.0
fTanHalfFov     REAL4 0.66817864   ; tan(48 * PI / 256) = tan(33.75 deg)
fRadToAngle     REAL4 81.48733     ; 256.0 / PI

.code

; ------------------------------------------------------------------------------
; InitMathTables: Builds 512-entry Sin & Cos tables in 16.16 fixed point,
; and 320-entry tangential ray angle offset table for flat-plane projection.
; ------------------------------------------------------------------------------
InitMathTables PROC uses eax ecx edi
    LOCAL curVal:DWORD

    ; 1. Generate 512-entry Sin/Cos tables
    mov ecx, 0
init_angle_loop:
    mov curVal, ecx

    fldpi
    fimul curVal
    fdiv fAngleDiv              ; st(0) = (angle * PI) / 256

    fsincos                     ; st(0) = cos, st(1) = sin

    ; Process Cosine
    fmul fFixedScale
    fistp DWORD PTR [tableCos + ecx*4]

    ; Process Sine
    fmul fFixedScale
    fistp DWORD PTR [tableSin + ecx*4]

    inc ecx
    cmp ecx, ANGLE_512
    jl init_angle_loop

    ; 2. Generate 320-entry Ray Angle Offset table (tangential perspective correction)
    ; and precomputed cosine table for instant fish-eye correction.
    ; angleOffset = round( atan(((x - 160.0) / 160.0) * tan(FOV/2)) * (256.0 / PI) )
    mov ecx, 0
init_ray_loop:
    mov curVal, ecx

    fild curVal                 ; st(0) = x
    fsub fScreenHalfW           ; st(0) = x - 160.0
    fdiv fScreenHalfW           ; st(0) = (x - 160.0) / 160.0 = cameraX
    fmul fTanHalfFov            ; st(0) = cameraX * tan(FOV/2)
    fld1                        ; st(0) = 1.0, st(1) = cameraX * tan(FOV/2)
    fpatan                      ; st(0) = atan(st(1)/st(0)) = radOffset
    fmul fRadToAngle            ; st(0) = radOffset * (256.0 / PI)
    fistp DWORD PTR [tableRayAngleOffset + ecx*4]

    ; Precompute tableRayCos[ecx] = cos(angleOffset)
    mov eax, DWORD PTR [tableRayAngleOffset + ecx*4]
    and eax, ANGLE_MASK
    mov edx, [tableCos + eax*4]
    mov DWORD PTR [tableRayCos + ecx*4], edx

    inc ecx
    cmp ecx, SCREEN_W
    jl init_ray_loop

    ret
InitMathTables ENDP

; ------------------------------------------------------------------------------
; RandomRange: Generates pseudo-random uint in [0, maxVal-1]
; Input: maxVal (eax)
; Output: eax
; ------------------------------------------------------------------------------
RandomRange PROC uses ecx edx, maxVal:DWORD
    cmp maxVal, 1
    jle rand_zero

    mov eax, rngSeed
    imul eax, 1103515245
    add eax, 12345
    mov rngSeed, eax

    shr eax, 16
    xor edx, edx
    div maxVal
    mov eax, edx
    ret

rand_zero:
    xor eax, eax
    ret
RandomRange ENDP

; ------------------------------------------------------------------------------
; FixedMul: Multiplies two 16.16 fixed-point numbers
; Input: a, b
; Output: eax = (a * b) >> 16
; ------------------------------------------------------------------------------
FixedMul PROC uses edx, valA:DWORD, valB:DWORD
    mov eax, valA
    imul valB
    shrd eax, edx, 16
    ret
FixedMul ENDP

; ------------------------------------------------------------------------------
; FixedDiv: Divides two 16.16 fixed-point numbers
; Input: a, b
; Output: eax = (a << 16) / b
; ------------------------------------------------------------------------------
FixedDiv PROC uses ebx edx, valA:DWORD, valB:DWORD
    mov eax, valA
    mov ebx, valB
    test ebx, ebx
    jz div_zero

    cdq
    shld edx, eax, 16
    shl eax, 16
    idiv ebx
    ret

div_zero:
    mov eax, 7FFFFFFFh          ; Return max int on divide-by-zero
    ret
FixedDiv ENDP

; ------------------------------------------------------------------------------
; ClampInt: Clamps value between minVal and maxVal
; ------------------------------------------------------------------------------
ClampInt PROC val:DWORD, minVal:DWORD, maxVal:DWORD
    mov eax, val
    cmp eax, minVal
    jge @F
    mov eax, minVal
    ret
@@:
    cmp eax, maxVal
    jle @F
    mov eax, maxVal
@@:
    ret
ClampInt ENDP