weston/libweston/vertex-clipping.c

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/*
* Copyright © 2012 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice (including the
* next paragraph) shall be included in all copies or substantial
* portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <assert.h>
#include <float.h>
#include <math.h>
#include "shared/helpers.h"
#include "vertex-clipping.h"
WESTON_EXPORT_FOR_TESTS float
float_difference(float a, float b)
{
/* https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/ */
static const float max_diff = 4.0f * FLT_MIN;
static const float max_rel_diff = 4.0e-5;
float diff = a - b;
float adiff = fabsf(diff);
if (adiff <= max_diff)
return 0.0f;
a = fabsf(a);
b = fabsf(b);
if (adiff <= (a > b ? a : b) * max_rel_diff)
return 0.0f;
return diff;
}
/* A line segment (p1x, p1y)-(p2x, p2y) intersects the line x = x_arg.
* Compute the y coordinate of the intersection.
*/
static float
clip_intersect_y(float p1x, float p1y, float p2x, float p2y,
float x_arg)
{
float a;
float diff = float_difference(p1x, p2x);
/* Practically vertical line segment, yet the end points have already
* been determined to be on different sides of the line. Therefore
* the line segment is part of the line and intersects everywhere.
* Return the end point, so we use the whole line segment.
*/
if (diff == 0.0f)
return p2y;
a = (x_arg - p2x) / diff;
return p2y + (p1y - p2y) * a;
}
/* A line segment (p1x, p1y)-(p2x, p2y) intersects the line y = y_arg.
* Compute the x coordinate of the intersection.
*/
static float
clip_intersect_x(float p1x, float p1y, float p2x, float p2y,
float y_arg)
{
float a;
float diff = float_difference(p1y, p2y);
/* Practically horizontal line segment, yet the end points have already
* been determined to be on different sides of the line. Therefore
* the line segment is part of the line and intersects everywhere.
* Return the end point, so we use the whole line segment.
*/
if (diff == 0.0f)
return p2x;
a = (y_arg - p2y) / diff;
return p2x + (p1x - p2x) * a;
}
enum path_transition {
PATH_TRANSITION_OUT_TO_OUT = 0,
PATH_TRANSITION_OUT_TO_IN = 1,
PATH_TRANSITION_IN_TO_OUT = 2,
PATH_TRANSITION_IN_TO_IN = 3,
};
static void
clip_append_vertex(struct clip_context *ctx, float x, float y)
{
ctx->vertices->x = x;
ctx->vertices->y = y;
ctx->vertices++;
}
static enum path_transition
path_transition_left_edge(struct clip_context *ctx, float x, float y)
{
return ((ctx->prev.x >= ctx->clip.x1) << 1) | (x >= ctx->clip.x1);
}
static enum path_transition
path_transition_right_edge(struct clip_context *ctx, float x, float y)
{
return ((ctx->prev.x < ctx->clip.x2) << 1) | (x < ctx->clip.x2);
}
static enum path_transition
path_transition_top_edge(struct clip_context *ctx, float x, float y)
{
return ((ctx->prev.y >= ctx->clip.y1) << 1) | (y >= ctx->clip.y1);
}
static enum path_transition
path_transition_bottom_edge(struct clip_context *ctx, float x, float y)
{
return ((ctx->prev.y < ctx->clip.y2) << 1) | (y < ctx->clip.y2);
}
static void
clip_polygon_leftright(struct clip_context *ctx,
enum path_transition transition,
float x, float y, float clip_x)
{
float yi;
switch (transition) {
case PATH_TRANSITION_IN_TO_IN:
clip_append_vertex(ctx, x, y);
break;
case PATH_TRANSITION_IN_TO_OUT:
yi = clip_intersect_y(ctx->prev.x, ctx->prev.y, x, y, clip_x);
clip_append_vertex(ctx, clip_x, yi);
break;
case PATH_TRANSITION_OUT_TO_IN:
yi = clip_intersect_y(ctx->prev.x, ctx->prev.y, x, y, clip_x);
clip_append_vertex(ctx, clip_x, yi);
clip_append_vertex(ctx, x, y);
break;
case PATH_TRANSITION_OUT_TO_OUT:
/* nothing */
break;
default:
assert(0 && "bad enum path_transition");
}
ctx->prev.x = x;
ctx->prev.y = y;
}
static void
clip_polygon_topbottom(struct clip_context *ctx,
enum path_transition transition,
float x, float y, float clip_y)
{
float xi;
switch (transition) {
case PATH_TRANSITION_IN_TO_IN:
clip_append_vertex(ctx, x, y);
break;
case PATH_TRANSITION_IN_TO_OUT:
xi = clip_intersect_x(ctx->prev.x, ctx->prev.y, x, y, clip_y);
clip_append_vertex(ctx, xi, clip_y);
break;
case PATH_TRANSITION_OUT_TO_IN:
xi = clip_intersect_x(ctx->prev.x, ctx->prev.y, x, y, clip_y);
clip_append_vertex(ctx, xi, clip_y);
clip_append_vertex(ctx, x, y);
break;
case PATH_TRANSITION_OUT_TO_OUT:
/* nothing */
break;
default:
assert(0 && "bad enum path_transition");
}
ctx->prev.x = x;
ctx->prev.y = y;
}
static void
clip_context_prepare(struct clip_context *ctx, const struct polygon8 *src,
struct clip_vertex *dst)
{
ctx->prev.x = src->pos[src->n - 1].x;
ctx->prev.y = src->pos[src->n - 1].y;
ctx->vertices = dst;
}
static int
clip_polygon_left(struct clip_context *ctx, const struct polygon8 *src,
struct clip_vertex *dst)
{
enum path_transition trans;
int i;
if (src->n < 2)
return 0;
clip_context_prepare(ctx, src, dst);
for (i = 0; i < src->n; i++) {
trans = path_transition_left_edge(ctx, src->pos[i].x, src->pos[i].y);
clip_polygon_leftright(ctx, trans, src->pos[i].x, src->pos[i].y,
ctx->clip.x1);
}
return ctx->vertices - dst;
}
static int
clip_polygon_right(struct clip_context *ctx, const struct polygon8 *src,
struct clip_vertex *dst)
{
enum path_transition trans;
int i;
if (src->n < 2)
return 0;
clip_context_prepare(ctx, src, dst);
for (i = 0; i < src->n; i++) {
trans = path_transition_right_edge(ctx, src->pos[i].x, src->pos[i].y);
clip_polygon_leftright(ctx, trans, src->pos[i].x, src->pos[i].y,
ctx->clip.x2);
}
return ctx->vertices - dst;
}
static int
clip_polygon_top(struct clip_context *ctx, const struct polygon8 *src,
struct clip_vertex *dst)
{
enum path_transition trans;
int i;
if (src->n < 2)
return 0;
clip_context_prepare(ctx, src, dst);
for (i = 0; i < src->n; i++) {
trans = path_transition_top_edge(ctx, src->pos[i].x, src->pos[i].y);
clip_polygon_topbottom(ctx, trans, src->pos[i].x, src->pos[i].y,
ctx->clip.y1);
}
return ctx->vertices - dst;
}
static int
clip_polygon_bottom(struct clip_context *ctx, const struct polygon8 *src,
struct clip_vertex *dst)
{
enum path_transition trans;
int i;
if (src->n < 2)
return 0;
clip_context_prepare(ctx, src, dst);
for (i = 0; i < src->n; i++) {
trans = path_transition_bottom_edge(ctx, src->pos[i].x, src->pos[i].y);
clip_polygon_topbottom(ctx, trans, src->pos[i].x, src->pos[i].y,
ctx->clip.y2);
}
return ctx->vertices - dst;
}
WESTON_EXPORT_FOR_TESTS int
clip_simple(struct clip_context *ctx,
struct polygon8 *surf,
struct clip_vertex *restrict vertices)
{
int i;
for (i = 0; i < surf->n; i++) {
vertices[i].x = CLIP(surf->pos[i].x, ctx->clip.x1, ctx->clip.x2);
vertices[i].y = CLIP(surf->pos[i].y, ctx->clip.y1, ctx->clip.y2);
}
return surf->n;
}
WESTON_EXPORT_FOR_TESTS int
clip_transformed(struct clip_context *ctx,
const struct polygon8 *surf,
struct clip_vertex *restrict vertices)
{
struct polygon8 p = *surf, tmp;
int i, n;
tmp.n = clip_polygon_left(ctx, &p, tmp.pos);
p.n = clip_polygon_right(ctx, &tmp, p.pos);
tmp.n = clip_polygon_top(ctx, &p, tmp.pos);
p.n = clip_polygon_bottom(ctx, &tmp, p.pos);
/* Get rid of duplicate vertices */
vertices[0] = p.pos[0];
n = 1;
for (i = 1; i < p.n; i++) {
if (float_difference(vertices[n - 1].x, p.pos[i].x) == 0.0f &&
float_difference(vertices[n - 1].y, p.pos[i].y) == 0.0f)
continue;
vertices[n] = p.pos[i];
n++;
}
if (float_difference(vertices[n - 1].x, p.pos[0].x) == 0.0f &&
float_difference(vertices[n - 1].y, p.pos[0].y) == 0.0f)
n--;
return n;
}
int
clip_quad(struct gl_quad *quad, pixman_box32_t *surf_rect,
struct clip_vertex *vertices)
{
struct clip_context ctx = {
.clip.x1 = surf_rect->x1,
.clip.y1 = surf_rect->y1,
.clip.x2 = surf_rect->x2,
.clip.y2 = surf_rect->y2,
};
int n;
/* Simple case: quad edges are parallel to surface rect edges, there
* will be either four or zero edges. We just need to clip the quad to
* the surface rect bounds and test for non-zero area:
*/
if (quad->axis_aligned) {
clip_simple(&ctx, &quad->vertices, vertices);
if ((vertices[0].x != vertices[1].x) &&
(vertices[0].y != vertices[2].y))
return 4;
else
return 0;
}
/* Transformed case: first, simple bounding box check to discard early a
* quad that does not intersect with the rect:
*/
if ((quad->bbox.x1 >= ctx.clip.x2) || (quad->bbox.x2 <= ctx.clip.x1) ||
(quad->bbox.y1 >= ctx.clip.y2) || (quad->bbox.y2 <= ctx.clip.y1))
return 0;
/* Then, use a general polygon clipping algorithm to clip the quad with
* each side of the surface rect. The algorithm is Sutherland-Hodgman,
* as explained in
* https://www.codeguru.com/cplusplus/polygon-clipping/
* but without looking at any of that code.
*/
n = clip_transformed(&ctx, &quad->vertices, vertices);
if (n < 3)
return 0;
return n;
}