xref: /dports/games/shockolate/systemshock-0.8.2-43-ga9eb1b93/src/Libraries/3D/Source/light.c

/*

Copyright (C) 2015-2018 Night Dive Studios, LLC.

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/
//
// $Source: r:/prj/lib/src/3d/RCS/light.asm $
// $Revision: 1.2 $
// $Author: jaemz $
// $Date: 1994/10/13 20:51:49 $
//
// Light routines
//

#include "3d.h"
#include "GlobalV.h"
#include "lg.h"

// prototypes
void check_for_near(void);
void scale_light_vec(void);
void g3_light_obj(g3s_phandle norm, g3s_phandle pos);
fix light_diff_raw(g3s_phandle src, g3s_phandle dest);
fix light_spec_raw(g3s_phandle src, g3s_phandle dest);
fix light_dands_raw(g3s_phandle src, g3s_phandle dest);

// look ma, a zero vector
g3s_phandle tmp1;
g3s_phandle tmp2;
g3s_vector zero_vec = {0, 0, 0};

// sets a light vector in source space directly
// this light vector has to be in user space so we can dot it with
// other vector
// g3_set_light_src(g3s_vector *l)
// takes eax, trashes esi,edi
void g3_set_light_src(g3s_vector *l) { _g3d_light_src = *l; }

// This should be called after a frames' angles and stuff have been
// set, does not need to be done per object
// void g3_eval_vec_light(void)
// Means you should be not near
void g3_eval_vec_light(void) {
    // needs to be rotated through view matrix
    g3_vec_rotate(&_g3d_light_vec, &_g3d_light_src, &_wtoo_matrix);
    scale_light_vec();
}

// should be normalized already
// multiply by _g3d_diff_light
// to set light intensity
void scale_light_vec(void) {
    _g3d_light_vec.gX = fix_mul(_g3d_light_vec.gX, _g3d_diff_light);
    _g3d_light_vec.gY = fix_mul(_g3d_light_vec.gY, _g3d_diff_light);
    _g3d_light_vec.gZ = fix_mul(_g3d_light_vec.gZ, _g3d_diff_light);
}

// transforms local light source into viewer coords in anticipation
// of calling g3_eval_loc_light.  Saves a transformation don't you know
// ideally you'd want to transform the view vec and light vec into
// object coords.  That way you wouldn't have to transform their normals
// at all.  The new 3d should provide inverse transforms.  That way things
// could be lit more cheaply
void g3_trans_loc_light(void) {
    g3s_phandle p;

    p = g3_rotate_point(&_g3d_light_src);
    _g3d_light_trans = *(g3s_vector *)p;
}

// evaluates light point relative to another point, src is in world coords
// and pos is already transformed into eye coords
// void g3_eval_loc_light(eax)//
void g3_eval_loc_light(g3s_phandle pos) {
    fix temp;

    // transform light src point to eye coords

    // take difference with pos, and unscale them
    temp = -(pos->gX - _g3d_light_trans.gX);
    _g3d_light_vec.gX = fix_div(temp, _matrix_scale.gX);

    temp = -(pos->gY - _g3d_light_trans.gY);
    _g3d_light_vec.gY = fix_div(temp, _matrix_scale.gY);

    temp = -(pos->gZ - _g3d_light_trans.gZ);
    _g3d_light_vec.gZ = fix_div(temp, _matrix_scale.gZ);

    // normalize vector
    g3_vec_normalize(&_g3d_light_vec);

    // multiply by diff and divide by scale
    // so dot product just works
    scale_light_vec();
}

// evaluate the view vector relative to a point
// similar to above except src is always 0,0,0
// pos in eax has to be transformed into viewer coords
// eax points to the point in 3d space
void g3_eval_view(g3s_phandle pos) {
    fix temp;

    _g3d_view_vec.gX = pos->gX - _view_position.gX;
    _g3d_view_vec.gY = pos->gY - _view_position.gY;
    _g3d_view_vec.gZ = pos->gZ - _view_position.gZ;

    // normalize
    g3_vec_normalize(&_g3d_view_vec);

    // multiply by spec and negate vector
    // since it currently points at the
    // point instead of the viewer
    // you might think, why not do this
    // afterwards, and you're right.  But only
    // only if this view vec only gets used once

    temp = -_g3d_spec_light;
    _g3d_view_vec.gX = fix_mul(_g3d_view_vec.gX, temp);
    _g3d_view_vec.gY = fix_mul(_g3d_view_vec.gY, temp);
    _g3d_view_vec.gZ = fix_mul(_g3d_view_vec.gZ, temp);
}

// takes the dot product of view and light, for specular light
// assumes both light_vec and view_vec have been evaluated already
// everything is normal and in object space
// void g3_eval_ldotv(void)
void g3_eval_ldotv(void) {
    // multiply and scale once to find true dotproduct.
    // I hate this scaling stuff.  Erg.
    // transforming the light and view vectors into object
    // space would avoid this entirely

    _g3d_ldotv = g3_vec_dotprod(&_g3d_light_vec, &_g3d_view_vec);
}

// Evaluates and sets light vectors as necessary at the start of
// an object.  Does view vec if SPEC is set.  Transforms light
// vector or point depending how LOC_LIGHT is set.  Use this if
// both light and view will be modelled as far.  In fact, make
// sure both are set as far, or you will be sorry.
// Evaluates at the object center.  If necessary, evaluates the
// ldotv for light and view
// void g3_eval_light_obj_cen(void)
// this could be optimized a bit more when both spec
// both spec and diff is true
// this should do eval vec as well, basically everything
void g3_eval_light_obj_cen(void) {
    DEBUG("%s: Call Mark if you see this", __FUNCTION__);

    // MLA - this routine is buggy as far as I can tell, it doesn't work at all
    // edi is never set or just happens to be set right, or it always falls
    // through the first test (non_local)

    /*    ; is local?
        test    _g3d_light_type,LT_LOC_LIGHT or LT_SPEC
        jz     non_local

        ; find center of object, duh, center is at 0,0,0
        ;lea     esi,zero_vec
        ;call    g3_rotate_point; this would be point in viewer space
        ; returns point in edi
        ;mov     tmp1,edi

        ; evaluate local light
        test    _g3d_light_type,LT_LOC_LIGHT
        jz      no_loc
        mov     eax,edi
        call    g3_eval_loc_light
        jmp     test_spec
        no_loc:
        call    g3_eval_vec_light

        ; is spec set?
        test_spec:
        test    _g3d_light_type,LT_SPEC
        jz     spec_done

        ; evaluate view
        ; view vector relative to zero is in _view_position
        ; already
        ;mov     eax,tmp1
        lea     eax,zero_vec    ;in reality should write a diff routine
        call    g3_eval_view

        call    g3_eval_ldotv

        spec_done:
        ;mov     edi,tmp1
        ;freepnt edi
        ret

        non_local:
        ; assumes you've transformed
        ; it already
        jmp    g3_eval_vec_light*/
}

// set your view to be straight ahead, use when using specular,
// and after the light has been evaluated.  This is ultra cheap hack
// to get view vector for a whole scene, just points straight in
void g3_eval_view_ahead(void) {
    // this is in view coords, need in
    // object coords, this won't work
    _g3d_view_vec.gX = 0;
    _g3d_view_vec.gY = 0;
    _g3d_view_vec.gZ = -0x01000;

    // now eval ldotv, hm.
    _g3d_ldotv = -_g3d_light_vec.gZ;
}

// check to see if local stuff has to get set and
// set it if necessary
// takes args in tmp1,tmp2
void check_for_near(void) {
    if (!(_g3d_light_type & (LT_NEAR_VIEW | LT_NEAR_LIGHT)))
        return;

    // if light near, evaluate
    if (_g3d_light_type & LT_NEAR_LIGHT)
        g3_eval_loc_light(tmp2);

    // if view near, eval
    if (_g3d_light_type & LT_NEAR_VIEW)
        g3_eval_view(tmp2);

    // evaluate ldotv if either was local
    // MLA - this is stupid, the code that tests for whether or not to call
    // g3_eval_ldotv makes no sense, it does a JZ on an undetermined condition
    // code setup.  So I just call it all the time. Look in Light.ASM in the PC 3D
    // code for the original stuff.
    g3_eval_ldotv();
}

// void g3_light_diff(g3s_phandle norm,g3s_phandle pos)//
// takes normal vector transformed, dots with the light vec,
// puts light val in norm,
// takes args in [eax,edx]
void g3_light_diff(g3s_phandle norm, g3s_phandle pos) {
    // push eax if not gouraud, or edx if, so we know
    // whether to light the normal or the point
    // maybe we could make this self modifying based
    // on a light type setter, if this is slow

    // MLA - whatever, I made it normal C code

    tmp1 = norm;
    tmp2 = pos;
    check_for_near();

    if ((_g3d_light_type & LT_GOUR) == 0)
        light_diff_raw(tmp1, norm);
    else
        light_diff_raw(tmp1, pos);
}

// raw version
// dot product with normal
// esi and edi
// ret eax
fix light_diff_raw(g3s_phandle src, g3s_phandle dest) {
    fix temp;

    temp = g3_vec_dotprod(&_g3d_light_vec, (g3s_vector *)src);

    // set lighting value in norm
    // test eax for negativity, zero if negative
    if (temp < 0)
        temp = 0;
    temp += _g3d_amb_light; // add ambient light
    temp >>= 4;             // convert to sfix, consider row 16 normal
    dest->i = temp;
    return (temp);
}

// void g3_light_spec(g3s_phandle norm,g3s_phandle pos)//
// takes norm and point position, lights point
// could both be the same, of course [eax,edx]
void g3_light_spec(g3s_phandle norm, g3s_phandle pos) {
    // push eax if not gouraud, or edx if, so we know
    // whether to light the normal or the point
    // maybe we could make this self modifying based
    // on a light type setter, if this is slow

    // MLA - whatever, I made it normal C code

    // save norm and pos off so we don't push and
    // pop them forever
    tmp1 = norm;
    tmp2 = pos;
    check_for_near();

    if ((_g3d_light_type & LT_GOUR) == 0)
        light_spec_raw(tmp1, norm);
    else
        light_spec_raw(tmp1, pos);
}

// pure specular lighting is equal to
// 2(s.l)(s.v) - (l.v)
// take (s.l)
fix light_spec_raw(g3s_phandle src, g3s_phandle dest) {
    fix temp;

    temp = g3_vec_dotprod(&_g3d_light_vec, (g3s_vector *)src);
    if (temp < 0) {
        dest->i = _g3d_amb_light >> 4;
        return (dest->i);
    }

    _g3d_sdotl = temp;

    // take (s.v), note that this is jnorm, if its been done
    // we can eliminate this step intelligently somehow
    _g3d_sdotv = temp = g3_vec_dotprod(&_g3d_view_vec, (g3s_vector *)tmp1);
    temp <<= 1;                       // multiply (s.v) by 2
    temp = fix_mul(temp, _g3d_sdotl); // mult by (s.l)
    temp -= _g3d_ldotv;               // subtract ldotv, done!

    // test eax for flash point zero if under
    // or better test eax for spec threshhold
    if (temp < _g3d_flash)
        temp = 0;

    // add ambient light
    temp += _g3d_amb_light;

    // check to see if its greater than the max row
    // and truncate if it is
    if (temp >= (LT_TABSIZE << 12))
        ;
    temp = (LT_TABSIZE << 12) - 1; // if its over the max, set it to just under max

    dest->i = temp >> 4; // convert to sfix, consider row 16 normal
    return (temp);
}

// void g3_light_dands(g3s_phandle norm,g3s_phandle pos)//
// lights with both diff and spec
//[eax,edx]
void g3_light_dands(g3s_phandle norm, g3s_phandle pos) {
    // MLA - same stuff as before, changed to C....
    tmp1 = norm;
    tmp2 = pos;
    check_for_near();

    if ((_g3d_light_type & LT_GOUR) == 0)
        light_dands_raw(tmp1, norm);
    else
        light_dands_raw(tmp1, pos);
}

// raw version of dands without local checking
fix light_dands_raw(g3s_phandle src, g3s_phandle dest) {
    fix temp;

    // pure specular lighting is equal to
    // 2(s.l)(s.v) - (l.v)
    // take (s.l) if neg, you know you're done, surface HAS to face the light

    temp = g3_vec_dotprod(&_g3d_light_vec, (g3s_vector *)src);
    if (temp < 0) {
        dest->i = _g3d_amb_light >> 4;
        return (dest->i);
    }
    _g3d_sdotl = temp;

    // take (s.v), note that this is jnorm, if its been done
    // we can eliminate this step intelligently somehow
    _g3d_sdotv = temp = g3_vec_dotprod(&_g3d_view_vec, (g3s_vector *)tmp1);
    temp = fix_mul(temp, _g3d_sdotl); // mult by (s.l)
    temp <<= 1;                       // multiply (s.v)(s.l) by 2
    temp -= _g3d_ldotv;               // subtract ldotv, done!

    // test eax for flash point zero if under
    // or better test eax for spec threshhold
    if (temp < _g3d_flash)
        temp = 0;

    // add diffuse component & ambient light
    temp += _g3d_sdotl + _g3d_amb_light;

    // check to see if its greater than the max row
    // and truncate if it is
    if (temp >= (LT_TABSIZE << 12))
        temp = (LT_TABSIZE << 12) - 1; // if its over the max, set it to just under max

    dest->i = temp >> 4; // convert to sfix, consider row 16 normal
    return (temp);
}

// farms out a point based on flags
// void g3_light(g3s_phandle norm,g3s_phandle pos)//
//[eax,edx]
fix g3_light(g3s_phandle norm, g3s_phandle pos) {
    g3s_phandle temp;

    if ((_g3d_light_type & LT_GOUR) == 0)
        temp = norm;
    else
        temp = pos;

    tmp1 = norm;
    tmp2 = pos;

    if ((_g3d_light_type & (LT_NEAR_VIEW | LT_NEAR_LIGHT)) != 0)
        check_for_near();

    // determine which routine to jump to based on flags
    switch (_g3d_light_type) {
    case LT_DIFF:
        return (light_diff_raw(tmp1, temp));
    case LT_SPEC:
        return (light_spec_raw(tmp1, temp));
    default:
        return (light_dands_raw(tmp1, temp));
    }
}

// farms out a point based on flags
// void g3_light_obj(g3s_vector *norm,g3s_vector *pos)//
//[eax,edx]
// norm is set with only 15 bits of fraction, pos is normal
// all vectors are in object space
// though we put these in points, they are in object space,
// not world space
void g3_light_obj(g3s_phandle norm, g3s_phandle pos) {
    g3s_point *norm_point;
    g3s_point *pos_point;
    fix shade;

    tmp1 = norm;
    tmp2 = pos;
    getpnt(norm_point);

    norm_point->gX = norm->gX << 1;
    norm_point->gY = norm->gY << 1;
    norm_point->gZ = norm->gZ << 1;

    // Copy position over to its own point
    getpnt(pos_point);
    *(g3s_vector *)pos_point = *(g3s_vector *)pos;

    shade = g3_light(norm_point, pos_point);

    // set the lighting when non gouraud
    // set fill type to address of shading table
    shade &= 0xffffff00;
    shade += _g3d_light_tab;

    gr_set_fill_parm(shade);

    freepnt(norm_point);
    freepnt(pos_point);
}

// generic list gronker, farms these points out
// call this inside an object or inside a frame
// at any rate, the points need to have been
// transformed
// g3_light_list(int n,g3s_phandle *norm,g3s_phandle *pos)
//  [eax,edx,ebx]
void g3_light_list(int n, g3s_phandle *norm, g3s_phandle *pos) {}