calculations.qc

Go to the documentation of this file.

#include "calculations.qh"

// =============================
//  Explosion Force Calculation
// =============================

float explosion_calcpush_getmultiplier(vector explosion_v, vector target_v)
{
    float a;
    a  = explosion_v * (explosion_v - target_v);

    if(a <= 0)
        // target is too fast to be hittable by this
        return 0;

    a /= (explosion_v * explosion_v);
        // we know we can divide by this, or above a would be == 0

    return a;
}

#if 0
vector explosion_calcpush(vector explosion_v, float explosion_m, vector target_v, float target_m, float elasticity)
{
    // solution of the equations:
    //    v'                = v + a vp             // central hit
    //    m*v'   + mp*vp'   = m*v + mp*vp          // conservation of momentum
    //    m*v'^2 + mp*vp'^2 = m*v^2 + mp*vp^2      // conservation of energy (ELASTIC hit)
    // -> a = 0                                    // case 1: did not hit
    // -> a = 2*mp*(vp^2 - vp.v) / ((m+mp) * vp^2) // case 2: did hit
    //                                             // non-elastic hits are somewhere between these two

    // this would be physically correct, but we don't do that
    return explosion_v * explosion_calcpush_getmultiplier(explosion_v, target_v) * (
        (1 + elasticity) * (
            explosion_m
        ) / (
            target_m + explosion_m
        )
    ); // note: this factor is at least 0, at most 2
}
#endif

// simplified formula, tuned so that if the target has velocity 0, we get exactly the original force
vector damage_explosion_calcpush(vector explosion_f, vector target_v, float speedfactor)
{
    // if below 1, the formulas make no sense (and would cause superjumps)
    if(speedfactor < 1)
        return explosion_f;

#if 0
    float m;
    // find m so that
    //   speedfactor * (1 + e) * m / (1 + m) == 1
    m = 1 / ((1 + 0) * speedfactor - 1);
    vector v;
    v = explosion_calcpush(explosion_f * speedfactor, m, target_v, 1, 0);
    // the factor we then get is:
    //   1
    LOG_INFOF("MASS: %f\nv: %v -> %v\nENERGY BEFORE == %f + %f = %f\nENERGY AFTER >= %f",
        m,
        target_v, target_v + v,
        target_v * target_v, m * explosion_f * speedfactor * explosion_f * speedfactor, target_v * target_v + m * explosion_f * speedfactor * explosion_f * speedfactor,
        (target_v + v) * (target_v + v));
    return v;
#endif
    return explosion_f * explosion_calcpush_getmultiplier(explosion_f * speedfactor, target_v);
}


// =========================
//  Shot Spread Calculation
// =========================

vector cliptoplane(vector v, vector p)
{
    return v - (v * p) * p;
}

vector solve_cubic_pq(float p, float q)
{
    float D, u, v, a;
    D = q*q/4.0 + p*p*p/27.0;
    if(D < 0)
    {
        // irreducibilis
        a = 1.0/3.0 * acos(-q/2.0 * sqrt(-27.0/(p*p*p)));
        u = sqrt(-4.0/3.0 * p);
        // a in range 0..pi/3
        // cos(a)
        // cos(a + 2pi/3)
        // cos(a + 4pi/3)
        return u * vec3(
            cos(a + 2.0/3.0*M_PI),
            cos(a + 4.0/3.0*M_PI),
            cos(a)
        );
    }
    else if(D == 0)
    {
        // simple
        if(p == 0)
            return '0 0 0';
        u = 3*q/p;
        v = -u/2;
        return (u >= v) ? vec3(v, v, u) : vec3(u, v, v);
    }
    else
    {
        // cardano
        //u = cbrt(-q/2.0 + sqrt(D));
        //v = cbrt(-q/2.0 - sqrt(D));
        a = cbrt(-q/2.0 + sqrt(D)) + cbrt(-q/2.0 - sqrt(D));
        return vec3(a, a, a);
    }
}
vector solve_cubic_abcd(float a, float b, float c, float d)
{
    // y = 3*a*x + b
    // x = (y - b) / 3a
    float p, q;
    vector v;
    p = (9*a*c - 3*b*b);
    q = (27*a*a*d - 9*a*b*c + 2*b*b*b);
    v = solve_cubic_pq(p, q);
    v = (v -  b * '1 1 1') * (1.0 / (3.0 * a));
    if(a < 0)
        v += '1 0 -1' * (v.z - v.x); // swap x, z
    return v;
}

vector findperpendicular(vector v)
{
    return normalize(cliptoplane(vec3(v.z, -v.x, v.y), v));
}

#ifdef SVQC
    int W_GunAlign(entity this, int preferred_align)
    {
        if(this.m_gunalign)
            return this.m_gunalign; // no adjustment needed

        entity own = this.owner;

        if(preferred_align < 1 || preferred_align > 4)
            preferred_align = 3; // default

        for(int j = 4; j > 1; --j) // > 1 as 1 is just center again
        {
            int taken = 0;
            for(int slot = 0; slot < MAX_WEAPONSLOTS; ++slot)
            {
                .entity weaponentity = weaponentities[slot];
                if(own.(weaponentity).m_gunalign == j) // we know it can't be ours thanks to the above check
                    taken |= BIT(j);
                if(own.(weaponentity).m_gunalign == preferred_align)
                    taken |= BIT(preferred_align);
            }

            if(!(taken & BIT(preferred_align)))
                return preferred_align; // prefer the recommended
            if(!(taken & BIT(j)))
                return j; // or fall back if it's not available
        }

        return preferred_align; // return it anyway
    }
#else
    int W_GunAlign(entity this, int preferred_align)
    {
        return this.m_gunalign > 0 ? this.m_gunalign : preferred_align;
    }
#endif

#if 0
int W_GetGunAlignment(entity player)
{
    int gunalign = STAT(GUNALIGN, player);
    if(gunalign < 1 || gunalign > 4)
        gunalign = 3; // default value
    --gunalign;

    return gunalign;
}
#endif

vector W_CalculateSpread(vector forward, float spread, float spreadfactor, float spreadstyle)
{
    float sigma;
    vector v1 = '0 0 0', v2;
    float dx, dy, r;
    spread *= spreadfactor; //autocvar_g_weaponspreadfactor;
    if(spread <= 0)
        return forward;

    switch(spreadstyle)
    {
        case 0:
        {
            // this is the baseline for the spread value!
            // standard deviation: sqrt(2/5)
            // density function: sqrt(1-r^2)
            return forward + randomvec() * spread;
        }
        case 1:
        {
            // same thing, basically
            return normalize(forward + cliptoplane(randomvec() * spread, forward));
        }
        case 2:
        {
            // circle spread... has at sigma=1 a standard deviation of sqrt(1/2)
            sigma = spread * 0.89442719099991587855; // match baseline stddev
            v1 = findperpendicular(forward);
            v2 = cross(forward, v1);
            // random point on unit circle
            dx = random() * 2 * M_PI;
            dy = sin(dx);
            dx = cos(dx);
            // radius in our dist function
            r = random();
            r = sqrt(r);
            return normalize(forward + (v1 * dx + v2 * dy) * r * sigma);
        }
        case 3: // gauss 3d
        {
            sigma = spread * 0.44721359549996; // match baseline stddev
            // note: 2D gaussian has sqrt(2) times the stddev of 1D, so this factor is right
            v1 = forward;
            v1_x += gsl_ran_gaussian(sigma);
            v1_y += gsl_ran_gaussian(sigma);
            v1_z += gsl_ran_gaussian(sigma);
            return v1;
        }
        case 4: // gauss 2d
        {
            sigma = spread * 0.44721359549996; // match baseline stddev
            // note: 2D gaussian has sqrt(2) times the stddev of 1D, so this factor is right
            v1_x = gsl_ran_gaussian(sigma);
            v1_y = gsl_ran_gaussian(sigma);
            v1_z = gsl_ran_gaussian(sigma);
            return normalize(forward + cliptoplane(v1, forward));
        }
        case 5: // 1-r
        {
            sigma = spread * 1.154700538379252; // match baseline stddev
            v1 = findperpendicular(forward);
            v2 = cross(forward, v1);
            // random point on unit circle
            dx = random() * 2 * M_PI;
            dy = sin(dx);
            dx = cos(dx);
            // radius in our dist function
            r = random();
            r = solve_cubic_abcd(-2, 3, 0, -r) * '0 1 0';
            return normalize(forward + (v1 * dx + v2 * dy) * r * sigma);
        }
        case 6: // 1-r^2
        {
            sigma = spread * 1.095445115010332; // match baseline stddev
            v1 = findperpendicular(forward);
            v2 = cross(forward, v1);
            // random point on unit circle
            dx = random() * 2 * M_PI;
            dy = sin(dx);
            dx = cos(dx);
            // radius in our dist function
            r = random();
            r = sqrt(1 - r);
            r = sqrt(1 - r);
            return normalize(forward + (v1 * dx + v2 * dy) * r * sigma);
        }
        case 7: // (1-r) (2-r)
        {
            sigma = spread * 1.224744871391589; // match baseline stddev
            v1 = findperpendicular(forward);
            v2 = cross(forward, v1);
            // random point on unit circle
            dx = random() * 2 * M_PI;
            dy = sin(dx);
            dx = cos(dx);
            // radius in our dist function
            r = random();
            r = 1 - sqrt(r);
            r = 1 - sqrt(r);
            return normalize(forward + (v1 * dx + v2 * dy) * r * sigma);
        }
        default:
            error("g_projectiles_spread_style must be 0 (sphere), 1 (flattened sphere), 2 (circle), 3 (gauss 3D), 4 (gauss plane), 5 (linear falloff), 6 (quadratic falloff), 7 (stronger falloff)!");
    }

    return '0 0 0';
    /*
     * how to derive falloff functions:
     * rho(r) := (2-r) * (1-r);
     * a : 0;
     * b : 1;
     * rhor(r) := r * rho(r);
     * cr(t) := integrate(rhor(r), r, a, t);
     * scr(t) := integrate(rhor(r) * r^2, r, a, t);
     * variance : scr(b) / cr(b);
     * solve(cr(r) = rand * cr(b), r), programmmode:false;
     * sqrt(0.4 / variance), numer;
     */
}