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/*
* Copyright (C) 2020 - Vito Caputo - <vcaputo@pengaru.com>
*
* This program is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 3 as published
* by the Free Software Foundation.
*
* 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/>.
*/
#include <assert.h>
#include <math.h>
#include <stdlib.h>
#include "puddle.h"
typedef struct puddle_t {
int w, h;
float *a, *b;
float floats[];
} puddle_t;
typedef struct v2f_t {
float x, y;
} v2f_t;
puddle_t * puddle_new(int w, int h)
{
puddle_t *puddle;
puddle = calloc(1, sizeof(puddle_t) + sizeof(float) * w * (h + 2) * 2);
if (!puddle)
return NULL;
puddle->w = w;
puddle->h = h;
puddle->a = &puddle->floats[w];
puddle->b = &puddle->floats[w * 2 + w * h + w];
return puddle;
}
void puddle_free(puddle_t *puddle)
{
free(puddle);
}
/* Run the puddle simulation for a tick, using the supplied viscosity value.
* A good viscosity value is ~.01, YMMV.
*/
void puddle_tick(puddle_t *puddle, float viscosity)
{
float *a, *b;
assert(puddle);
a = puddle->a;
b = puddle->b;
for (int y = 0, i = 0; y < puddle->h; y++) {
for (int x = 0; x < puddle->w; x++, i++) {
float tmp = a[i - puddle->w] +
a[i - 1] +
a[i + 1] +
a[i + puddle->w];
tmp -= b[i] * 2.f;
tmp *= .5f;
tmp -= tmp * viscosity;
b[i] = tmp;
}
}
puddle->b = a;
puddle->a = b;
}
/* Set a specific cell in the puddle to the supplied value */
void puddle_set(puddle_t *puddle, int x, int y, float value)
{
assert(puddle);
assert(x >= 0 && x < puddle->w);
assert(y >= 0 && y < puddle->h);
puddle->a[y * puddle->w + x] = value;
}
static inline float lerp(float a, float b, float t)
{
return (1.0f - t) * a + t * b;
}
/* Sample the supplied puddle field at the specified coordinate.
*
* The puddle field is treated as a unit square mapped to the specified
* dimensions @ create time. the sampled value is linearly interpolated from
* the data.
*/
float puddle_sample(const puddle_t *puddle, const v2f_t *coordinate)
{
int x0, y0, x1, y1;
float x, y, tx, ty;
assert(puddle);
assert(coordinate);
x = .5f + (coordinate->x * .5f + .5f) * (puddle->w - 2);
y = .5f + (coordinate->y * .5f + .5f) * (puddle->h - 2);
x0 = floorf(x);
y0 = floorf(y);
x1 = x0 + 1;
y1 = y0 + 1;
tx = x - (float)x0;
ty = y - (float)y0;
return lerp(lerp(puddle->a[y0 * puddle->w + x0], puddle->a[y0 * puddle->w + x1], tx),
lerp(puddle->a[y1 * puddle->w + x0], puddle->a[y1 * puddle->w + x1], tx),
ty);
}
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