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curve: Add gsk_curve_decompose_curve

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This is mainly useful for decomposing a conic into
cubics. The criterion here for terminating the
subdivision is very improvised.

But it also allows for other use cases, such as
raising the degree of quadratics to cubics.

An auxiliary API introduced here is gsk_curve_elevate.
This commit is contained in:
Matthias Clasen
2020-12-09 17:46:31 -05:00
parent e03585e89f
commit 4a9e4f5f9f
2 changed files with 261 additions and 0 deletions
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247
gsk/gskcurve.c
View File

@@ -52,6 +52,11 @@ struct _GskCurveClass
float tolerance,
GskCurveAddLineFunc add_line_func,
gpointer user_data);
gboolean (* decompose_curve) (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data);
gskpathop (* pathop) (const GskCurve *curve);
const graphene_point_t * (* get_start_point) (const GskCurve *curve);
const graphene_point_t * (* get_end_point) (const GskCurve *curve);
@@ -172,6 +177,18 @@ gsk_line_curve_decompose (const GskCurve *curve,
return add_line_func (&self->points[0], &self->points[1], 0.0f, 1.0f, GSK_CURVE_LINE_REASON_STRAIGHT, user_data);
}
static gboolean
gsk_line_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
const GskLineCurve *self = &curve->line;
return add_curve_func (GSK_PATH_LINE, self->points, 2, 0.f, user_data);
}
static gskpathop
gsk_line_curve_pathop (const GskCurve *curve)
{
@@ -224,6 +241,7 @@ static const GskCurveClass GSK_LINE_CURVE_CLASS = {
gsk_line_curve_split,
gsk_line_curve_segment,
gsk_line_curve_decompose,
gsk_line_curve_decompose_curve,
gsk_line_curve_pathop,
gsk_line_curve_get_start_point,
gsk_line_curve_get_end_point,
@@ -394,6 +412,60 @@ gsk_quad_curve_decompose (const GskCurve *curve,
return gsk_quad_curve_decompose_step (curve, 0.0, 1.0, tolerance, add_line_func, user_data);
}
typedef struct
{
GskCurveAddCurveFunc add_curve;
gpointer user_data;
} AddLineData;
static gboolean
gsk_curve_add_line_cb (const graphene_point_t *from,
const graphene_point_t *to,
float from_progress,
float to_progress,
GskCurveLineReason reason,
gpointer user_data)
{
AddLineData *data = user_data;
graphene_point_t p[2] = { *from, *to };
return data->add_curve (GSK_PATH_LINE, p, 2, 0.f, data->user_data);
}
static gboolean
gsk_quad_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
const GskQuadCurve *self = &curve->quad;
if (flags & GSK_PATH_FOREACH_ALLOW_QUAD)
return add_curve_func (GSK_PATH_QUAD, self->points, 3, 0.f, user_data);
else if (flags & GSK_PATH_FOREACH_ALLOW_CUBIC)
{
GskCurve c;
gsk_curve_elevate (curve, &c);
return add_curve_func (GSK_PATH_CUBIC, c.cubic.points, 4, 0.f, user_data);
}
else if (flags & GSK_PATH_FOREACH_ALLOW_CONIC)
{
GskCurve c;
gsk_curve_init_foreach (&c, GSK_PATH_CONIC, self->points, 3, 1.f);
return add_curve_func (GSK_PATH_CUBIC, c.cubic.points, 4, 0.f, user_data);
}
else
{
return gsk_quad_curve_decompose (curve,
tolerance,
gsk_curve_add_line_cb,
&(AddLineData) { add_curve_func, user_data });
}
}
static gskpathop
gsk_quad_curve_pathop (const GskCurve *curve)
{
@@ -457,6 +529,7 @@ static const GskCurveClass GSK_QUAD_CURVE_CLASS = {
gsk_quad_curve_split,
gsk_quad_curve_segment,
gsk_quad_curve_decompose,
gsk_quad_curve_decompose_curve,
gsk_quad_curve_pathop,
gsk_quad_curve_get_start_point,
gsk_quad_curve_get_end_point,
@@ -638,6 +711,25 @@ gsk_cubic_curve_decompose (const GskCurve *curve,
return gsk_curce_curve_decompose_step (curve, 0.0, 1.0, tolerance, add_line_func, user_data);
}
static gboolean
gsk_cubic_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
const GskCubicCurve *self = &curve->cubic;
if (flags & GSK_PATH_FOREACH_ALLOW_CUBIC)
return add_curve_func (GSK_PATH_CUBIC, self->points, 4, 0.f, user_data);
/* FIXME: Quadratic (or conic?) approximation */
return gsk_cubic_curve_decompose (curve,
tolerance,
gsk_curve_add_line_cb,
&(AddLineData) { add_curve_func, user_data });
}
static gskpathop
gsk_cubic_curve_pathop (const GskCurve *curve)
{
@@ -702,6 +794,7 @@ static const GskCurveClass GSK_CUBIC_CURVE_CLASS = {
gsk_cubic_curve_split,
gsk_cubic_curve_segment,
gsk_cubic_curve_decompose,
gsk_cubic_curve_decompose_curve,
gsk_cubic_curve_pathop,
gsk_cubic_curve_get_start_point,
gsk_cubic_curve_get_end_point,
@@ -1067,6 +1160,110 @@ gsk_conic_curve_decompose (const GskCurve *curve,
user_data);
}
/* See Floater, M: An analysis of cubic approximation schemes
* for conic sections
*/
static void
cubic_approximation (const GskCurve *curve,
GskCurve *cubic)
{
const GskConicCurve *self = &curve->conic;
graphene_point_t p[4];
float w = self->points[2].x;
float w2 = w*w;
float lambda;
lambda = 2 * (6*w2 + 1 - sqrt (3*w2 + 1)) / (12*w2 + 3);
p[0] = self->points[0];
p[3] = self->points[3];
graphene_point_interpolate (&self->points[0], &self->points[1], lambda, &p[1]);
graphene_point_interpolate (&self->points[3], &self->points[1], lambda, &p[2]);
gsk_curve_init (cubic, gsk_pathop_encode (GSK_PATH_CUBIC, p));
}
static gboolean
gsk_conic_is_close_to_cubic (const GskCurve *conic,
const GskCurve *cubic,
float tolerance)
{
float t[] = { 0.1, 0.5, 0.9 };
graphene_point_t p0, p1;
for (int i = 0; i < G_N_ELEMENTS (t); i++)
{
gsk_curve_get_point (conic, t[i], &p0);
gsk_curve_get_point (cubic, t[i], &p1);
if (graphene_point_distance (&p0, &p1, NULL, NULL) > tolerance)
return FALSE;
}
return TRUE;
}
static gboolean gsk_conic_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data);
static gboolean
gsk_conic_curve_decompose_or_add (const GskCurve *curve,
const GskCurve *cubic,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
if (gsk_conic_is_close_to_cubic (curve, cubic, tolerance))
return add_curve_func (GSK_PATH_CUBIC, cubic->cubic.points, 4, 0.f, user_data);
else
{
GskCurve c1, c2;
GskCurve cc1, cc2;
gsk_conic_curve_split (curve, 0.5, &c1, &c2);
cubic_approximation (&c1, &cc1);
cubic_approximation (&c2, &cc2);
return gsk_conic_curve_decompose_or_add (&c1, &cc1, tolerance, add_curve_func, user_data) &&
gsk_conic_curve_decompose_or_add (&c2, &cc2, tolerance, add_curve_func, user_data);
}
}
static gboolean
gsk_conic_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
const GskConicCurve *self = &curve->conic;
GskCurve c;
if (flags & GSK_PATH_FOREACH_ALLOW_CONIC)
return add_curve_func (GSK_PATH_CONIC,
(const graphene_point_t[3]) { self->points[0],
self->points[1],
self->points[3] },
3,
self->points[2].x,
user_data);
if (flags & GSK_PATH_FOREACH_ALLOW_CUBIC)
{
cubic_approximation (curve, &c);
return gsk_conic_curve_decompose_or_add (curve, &c, tolerance, add_curve_func, user_data);
}
/* FIXME: Quadratic (or conic?) approximation */
return gsk_conic_curve_decompose (curve,
tolerance,
gsk_curve_add_line_cb,
&(AddLineData) { add_curve_func, user_data });
}
static gskpathop
gsk_conic_curve_pathop (const GskCurve *curve)
{
@@ -1131,6 +1328,7 @@ static const GskCurveClass GSK_CONIC_CURVE_CLASS = {
gsk_conic_curve_split,
gsk_conic_curve_segment,
gsk_conic_curve_decompose,
gsk_conic_curve_decompose_curve,
gsk_conic_curve_pathop,
gsk_conic_curve_get_start_point,
gsk_conic_curve_get_end_point,
@@ -1225,6 +1423,16 @@ gsk_curve_decompose (const GskCurve *curve,
return get_class (curve->op)->decompose (curve, tolerance, add_line_func, user_data);
}
gboolean
gsk_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data)
{
return get_class (curve->op)->decompose_curve (curve, flags, tolerance, add_curve_func, user_data);
}
gskpathop
gsk_curve_pathop (const GskCurve *curve)
{
@@ -1263,3 +1471,42 @@ gsk_curve_reverse (const GskCurve *curve,
{
get_class (curve->op)->reverse (curve, reverse);
}
/* Replace a line by an equivalent quad,
* and a quad by an equivalent cubic.
*/
void
gsk_curve_elevate (const GskCurve *curve,
GskCurve *elevated)
{
if (curve->op == GSK_PATH_LINE)
{
graphene_point_t p[3];
p[0] = curve->line.points[0];
graphene_point_interpolate (&curve->line.points[0],
&curve->line.points[1],
0.5,
&p[1]);
p[2] = curve->line.points[1];
gsk_quad_curve_init_from_points (&elevated->quad, p);
}
else if (curve->op == GSK_PATH_QUAD)
{
graphene_point_t p[4];
p[0] = curve->quad.points[0];
graphene_point_interpolate (&curve->quad.points[0],
&curve->quad.points[1],
2/3.,
&p[1]);
graphene_point_interpolate (&curve->quad.points[2],
&curve->quad.points[1],
2/3.,
&p[2]);
p[3] = curve->quad.points[2];
gsk_cubic_curve_init_from_points (&elevated->cubic, p);
}
else
g_assert_not_reached ();
}

14
gsk/gskcurveprivate.h
View File

@@ -22,6 +22,7 @@
#define __GSK_CURVE_PRIVATE_H__
#include "gskpathopprivate.h"
#include "gskpath.h"
G_BEGIN_DECLS
@@ -101,6 +102,12 @@ typedef gboolean (* GskCurveAddLineFunc) (const graphene_point_t *from,
GskCurveLineReason reason,
gpointer user_data);
typedef gboolean (* GskCurveAddCurveFunc) (GskPathOperation op,
const graphene_point_t *pts,
gsize n_pts,
float weight,
gpointer user_data);
void gsk_curve_init (GskCurve *curve,
gskpathop op);
void gsk_curve_init_foreach (GskCurve *curve,
@@ -127,6 +134,11 @@ gboolean gsk_curve_decompose (const GskCurve
float tolerance,
GskCurveAddLineFunc add_line_func,
gpointer user_data);
gboolean gsk_curve_decompose_curve (const GskCurve *curve,
GskPathForeachFlags flags,
float tolerance,
GskCurveAddCurveFunc add_curve_func,
gpointer user_data);
gskpathop gsk_curve_pathop (const GskCurve *curve);
#define gsk_curve_builder_to(curve, builder) gsk_path_builder_pathop_to ((builder), gsk_curve_pathop (curve))
const graphene_point_t *gsk_curve_get_start_point (const GskCurve *curve);
@@ -137,6 +149,8 @@ void gsk_curve_get_end_tangent (const GskCurve
graphene_vec2_t *tangent);
void gsk_curve_reverse (const GskCurve *curve,
GskCurve *reverse);
void gsk_curve_elevate (const GskCurve *curve,
GskCurve *elevated);
G_END_DECLS