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clutter/clutter/clutter-bezier.c

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/*
* Clutter.
*
* An OpenGL based 'interactive canvas' library.
*
* Authored By Tomas Frydrych <tf@openedhand.com>
*
* Copyright (C) 2007 OpenedHand
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
#include <glib.h>
#include <string.h>
#include "clutter-bezier.h"
#include "clutter-debug.h"
/*
* We have some experimental code here to allow for constant velocity
* movement of actors along the bezier path, this macro enables it.
*/
#undef CBZ_L2T_INTERPOLATION
/****************************************************************************
* ClutterBezier -- represenation of a cubic bezier curve *
* (private; a building block for the public bspline object) *
****************************************************************************/
/*
* The t parameter of the bezier is from interval <0,1>, so we can use
* 14.18 format and special multiplication functions that preserve
* more of the least significant bits but would overflow if the value
* is > 1
*/
#define CBZ_T_Q 18
#define CBZ_T_ONE (1 << CBZ_T_Q)
#define CBZ_T_MUL(x,y) ((((x) >> 3) * ((y) >> 3)) >> 12)
#define CBZ_T_POW2(x) CBZ_T_MUL (x, x)
#define CBZ_T_POW3(x) CBZ_T_MUL (CBZ_T_POW2 (x), x)
#define CBZ_T_DIV(x,y) ((((x) << 9)/(y)) << 9)
/*
* Constants for sampling of the bezier
*/
#define CBZ_T_SAMPLES 128
#define CBZ_T_STEP (CBZ_T_ONE / CBZ_T_SAMPLES)
#define CBZ_L_STEP (CBZ_T_ONE / CBZ_T_SAMPLES)
typedef gint32 _FixedT;
/*
* This is a private type representing a single cubic bezier
*/
struct _ClutterBezier
{
/*
* bezier coefficients -- these are calculated using multiplication and
* addition from integer input, so these are also integers
*/
gint ax;
gint bx;
gint cx;
gint dx;
gint ay;
gint by;
gint cy;
gint dy;
/* length of the bezier */
guint length;
#ifdef CBZ_L2T_INTERPOLATION
/*
* coefficients for the L -> t bezier; these are calculated from fixed
* point input, and more specifically numbers that have been normalised
* to fit <0,1>, so these are also fixed point, and we can used the
* _FixedT type here.
*/
_FixedT La;
_FixedT Lb;
_FixedT Lc;
/* _FixedT Ld; == 0 */
#endif
};
ClutterBezier *
_clutter_bezier_new (void)
{
return g_slice_new0 (ClutterBezier);
}
void
_clutter_bezier_free (ClutterBezier * b)
{
if (G_LIKELY (b))
{
g_slice_free (ClutterBezier, b);
}
}
ClutterBezier *
_clutter_bezier_clone_and_move (const ClutterBezier *b, gint x, gint y)
{
ClutterBezier * b2 = _clutter_bezier_new ();
memcpy (b2, b, sizeof (ClutterBezier));
b2->dx += x;
b2->dy += y;
return b2;
}
#ifdef CBZ_L2T_INTERPOLATION
/*
* L is relative advance along the bezier curve from interval <0,1>
*/
static _FixedT
_clutter_bezier_L2t (const ClutterBezier *b, _FixedT L)
{
_FixedT t = CBZ_T_MUL (b->La, CBZ_T_POW3(L))
+ CBZ_T_MUL (b->Lb, CBZ_T_POW2(L))
+ CBZ_T_MUL (b->Lc, L);
if (t > CBZ_T_ONE)
t = CBZ_T_ONE;
else if (t < 0)
t = 0;
return t;
}
#endif
static gint
_clutter_bezier_t2x (const ClutterBezier * b, _FixedT t)
{
/*
* NB -- the int coefficients can be at most 8192 for the multiplication
* to work in this fashion due to the limits of the 14.18 fixed.
*/
return ((b->ax*CBZ_T_POW3(t) + b->bx*CBZ_T_POW2(t) + b->cx*t) >> CBZ_T_Q)
+ b->dx;
}
static gint
_clutter_bezier_t2y (const ClutterBezier * b, _FixedT t)
{
/*
* NB -- the int coefficients can be at most 8192 for the multiplication
* to work in this fashion due to the limits of the 14.18 fixed.
*/
return ((b->ay*CBZ_T_POW3(t) + b->by*CBZ_T_POW2(t) + b->cy*t) >> CBZ_T_Q)
+ b->dy;
}
/*
* Advances along the bezier to relative length L and returns the coordinances
* in knot
*/
void
_clutter_bezier_advance (const ClutterBezier *b, gint L, ClutterKnot * knot)
{
#ifdef CBZ_L2T_INTERPOLATION
_FixedT t = clutter_bezier_L2t (b, L);
#else
_FixedT t = L;
#endif
knot->x = _clutter_bezier_t2x (b, t);
knot->y = _clutter_bezier_t2y (b, t);
CLUTTER_NOTE (MISC, "advancing to relative pt %f: t %f, {%d,%d}",
(double) L / (double) CBZ_T_ONE,
(double) t / (double) CBZ_T_ONE,
knot->x, knot->y);
}
void
_clutter_bezier_init (ClutterBezier *b,
gint x_0, gint y_0,
gint x_1, gint y_1,
gint x_2, gint y_2,
gint x_3, gint y_3)
{
_FixedT t;
int i;
int xp = x_0;
int yp = y_0;
_FixedT length [CBZ_T_SAMPLES + 1];
#ifdef CBZ_L2T_INTERPOLATION
int j, k;
_FixedT L;
_FixedT t_equalized [CBZ_T_SAMPLES + 1];
#endif
#if 0
g_debug ("Initializing bezier at {{%d,%d},{%d,%d},{%d,%d},{%d,%d}}",
x0, y0, x1, y1, x2, y2, x3, y3);
#endif
b->dx = x_0;
b->dy = y_0;
b->cx = 3 * (x_1 - x_0);
b->cy = 3 * (y_1 - y_0);
b->bx = 3 * (x_2 - x_1) - b->cx;
b->by = 3 * (y_2 - y_1) - b->cy;
b->ax = x_3 - 3 * x_2 + 3 * x_1 - x_0;
b->ay = y_3 - 3 * y_2 + 3 * y_1 - y_0;
#if 0
g_debug ("Cooeficients {{%d,%d},{%d,%d},{%d,%d},{%d,%d}}",
b->ax, b->ay, b->bx, b->by, b->cx, b->cy, b->dx, b->dy);
#endif
/*
* Because of the way we do the multiplication in bezeir_t2x,y
* these coefficients need to be at most 0x1fff; this should be the case,
* I think, but have added this warning to catch any problems -- if it
* triggers, we need to change those two functions a bit.
*/
if (b->ax > 0x1fff || b->bx > 0x1fff || b->cx > 0x1fff)
g_warning ("Calculated coefficents will result in multiplication "
"overflow in clutter_bezier_t2x and clutter_bezier_t2y.");
/*
* Sample the bezier with CBZ_T_SAMPLES and calculate length at
* each point.
*
* We are working with integers here, so we use the fast sqrti function.
*/
length[0] = 0;
for (t = CBZ_T_STEP, i = 1; i <= CBZ_T_SAMPLES; ++i, t += CBZ_T_STEP)
{
int x = _clutter_bezier_t2x (b, t);
int y = _clutter_bezier_t2y (b, t);
guint l = cogl_sqrti ((y - yp)*(y - yp) + (x - xp)*(x - xp));
l += length[i-1];
length[i] = l;
xp = x;
yp = y;
}
b->length = length[CBZ_T_SAMPLES];
#if 0
g_debug ("length %d", b->length);
#endif
#ifdef CBZ_L2T_INTERPOLATION
/*
* Now normalize the length values, converting them into _FixedT
*/
for (i = 0; i <= CBZ_T_SAMPLES; ++i)
{
length[i] = (length[i] << CBZ_T_Q) / b->length;
}
/*
* Now generate a L -> t table such that the L will equidistant
* over <0,1>
*/
t_equalized[0] = 0;
for (i = 1, j = 1, L = CBZ_L_STEP; i < CBZ_T_SAMPLES; ++i, L += CBZ_L_STEP)
{
_FixedT l1, l2;
_FixedT d1, d2, d;
_FixedT t1, t2;
/* find the band for our L */
for (k = j; k < CBZ_T_SAMPLES; ++k)
{
if (L < length[k])
break;
}
/*
* Now we know that L is from (length[k-1],length[k]>
* We remember k-1 in order not to have to iterate over the
* whole length array in the next iteration of the main loop
*/
j = k - 1;
/*
* Now interpolate equlised t as a weighted average
*/
l1 = length[k-1];
l2 = length[k];
d1 = l2 - L;
d2 = L - l1;
d = l2 - l1;
t1 = (k - 1) * CBZ_T_STEP;
t2 = k * CBZ_T_STEP;
t_equalized[i] = (t1*d1 + t2*d2)/d;
if (t_equalized[i] < t_equalized[i-1])
g_debug ("wrong t: L %f, l1 %f, l2 %f, t1 %f, t2 %f",
(double) (L)/(double)CBZ_T_ONE,
(double) (l1)/(double)CBZ_T_ONE,
(double) (l2)/(double)CBZ_T_ONE,
(double) (t1)/(double)CBZ_T_ONE,
(double) (t2)/(double)CBZ_T_ONE);
}
t_equalized[CBZ_T_SAMPLES] = CBZ_T_ONE;
/* We now fit a bezier -- at this stage, do a single fit through our values
* at 0, 1/3, 2/3 and 1
*
* FIXME -- do we need to use a better fitting approach to choose the best
* beziere. The actual curve we acquire this way is not too bad shapwise,
* but (probably due to rounding errors) the resulting curve no longer
* satisfies the necessary condition that for L2 > L1, t2 > t1, which
* causes oscilation.
*/
#if 0
/*
* These are the control points we use to calculate the curve coefficients
* for bezier t(L); these are not needed directly, but are implied in the
* calculations below.
*
* (p0 is 0,0, and p3 is 1,1)
*/
p1 = (18 * t_equalized[CBZ_T_SAMPLES/3] -
9 * t_equalized[2*CBZ_T_SAMPLES/3] +
2 << CBZ_T_Q) / 6;
p2 = (18 * t_equalized[2*CBZ_T_SAMPLES/3] -
9 * t_equalized[CBZ_T_SAMPLES/3] -
(5 << CBZ_T_Q)) / 6;
#endif
b->Lc = (18 * t_equalized[CBZ_T_SAMPLES/3] -
9 * t_equalized[2*CBZ_T_SAMPLES/3] +
(2 << CBZ_T_Q)) >> 1;
b->Lb = (36 * t_equalized[2*CBZ_T_SAMPLES/3] -
45 * t_equalized[CBZ_T_SAMPLES/3] -
(9 << CBZ_T_Q)) >> 1;
b->La = ((27 * (t_equalized[CBZ_T_SAMPLES/3] -
t_equalized[2*CBZ_T_SAMPLES/3]) +
(7 << CBZ_T_Q)) >> 1) + CBZ_T_ONE;
g_debug ("t(1/3) %f, t(2/3) %f",
(double)t_equalized[CBZ_T_SAMPLES/3]/(double)CBZ_T_ONE,
(double)t_equalized[2*CBZ_T_SAMPLES/3]/(double)CBZ_T_ONE);
g_debug ("L -> t coefficients: %f, %f, %f",
(double)b->La/(double)CBZ_T_ONE,
(double)b->Lb/(double)CBZ_T_ONE,
(double)b->Lc/(double)CBZ_T_ONE);
/*
* For debugging, you can load these values into a spreadsheet and graph
* them to see how well the approximation matches the data
*/
for (i = 0; i < CBZ_T_SAMPLES; ++i)
{
g_print ("%f, %f, %f\n",
(double)(i*CBZ_T_STEP)/(double)CBZ_T_ONE,
(double)(t_equalized[i])/(double)CBZ_T_ONE,
(double)(clutter_bezier_L2t(b,i*CBZ_T_STEP))/(double)CBZ_T_ONE);
}
#endif
}
/*
* Moves a control point at indx to location represented by knot
*/
void
_clutter_bezier_adjust (ClutterBezier * b, ClutterKnot * knot, guint indx)
{
guint x[4], y[4];
g_assert (indx < 4);
x[0] = b->dx;
y[0] = b->dy;
x[1] = b->cx / 3 + x[0];
y[1] = b->cy / 3 + y[0];
x[2] = b->bx / 3 + b->cx + x[1];
y[2] = b->by / 3 + b->cy + y[1];
x[3] = b->ax + x[0] + b->cx + b->bx;
y[3] = b->ay + y[0] + b->cy + b->by;
x[indx] = knot->x;
y[indx] = knot->y;
_clutter_bezier_init (b, x[0], y[0], x[1], y[1], x[2], y[2], x[3], y[3]);
}
guint
_clutter_bezier_get_length (const ClutterBezier *b)
{
return b->length;
}
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