413 lines
11 KiB
C
413 lines
11 KiB
C
/*
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* Copyright © 2012 Intel Corporation
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice (including the
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* next paragraph) shall be included in all copies or substantial
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* portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include <assert.h>
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#include <float.h>
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#include <math.h>
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#include <string.h>
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#include "shared/helpers.h"
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#include "vertex-clipping.h"
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struct clip_context {
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struct clipper_vertex prev;
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struct clipper_vertex box[2];
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struct clipper_vertex *vertices;
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};
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WESTON_EXPORT_FOR_TESTS float
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clipper_float_difference(float a, float b)
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{
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/* https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/ */
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static const float max_diff = 4.0f * FLT_MIN;
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static const float max_rel_diff = 4.0e-5;
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float diff = a - b;
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float adiff = fabsf(diff);
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if (adiff <= max_diff)
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return 0.0f;
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a = fabsf(a);
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b = fabsf(b);
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if (adiff <= (a > b ? a : b) * max_rel_diff)
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return 0.0f;
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return diff;
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}
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/* A line segment (p1x, p1y)-(p2x, p2y) intersects the line x = x_arg.
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* Compute the y coordinate of the intersection.
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*/
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static float
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clip_intersect_y(float p1x, float p1y, float p2x, float p2y,
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float x_arg)
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{
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float a;
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float diff = clipper_float_difference(p1x, p2x);
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/* Practically vertical line segment, yet the end points have already
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* been determined to be on different sides of the line. Therefore
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* the line segment is part of the line and intersects everywhere.
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* Return the end point, so we use the whole line segment.
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*/
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if (diff == 0.0f)
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return p2y;
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a = (x_arg - p2x) / diff;
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return p2y + (p1y - p2y) * a;
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}
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/* A line segment (p1x, p1y)-(p2x, p2y) intersects the line y = y_arg.
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* Compute the x coordinate of the intersection.
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*/
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static float
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clip_intersect_x(float p1x, float p1y, float p2x, float p2y,
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float y_arg)
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{
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float a;
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float diff = clipper_float_difference(p1y, p2y);
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/* Practically horizontal line segment, yet the end points have already
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* been determined to be on different sides of the line. Therefore
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* the line segment is part of the line and intersects everywhere.
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* Return the end point, so we use the whole line segment.
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*/
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if (diff == 0.0f)
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return p2x;
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a = (y_arg - p2y) / diff;
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return p2x + (p1x - p2x) * a;
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}
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enum path_transition {
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PATH_TRANSITION_OUT_TO_OUT = 0,
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PATH_TRANSITION_OUT_TO_IN = 1,
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PATH_TRANSITION_IN_TO_OUT = 2,
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PATH_TRANSITION_IN_TO_IN = 3,
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};
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static void
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clip_append_vertex(struct clip_context *ctx, float x, float y)
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{
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ctx->vertices->x = x;
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ctx->vertices->y = y;
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ctx->vertices++;
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}
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static enum path_transition
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path_transition_left_edge(struct clip_context *ctx, float x, float y)
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{
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return ((ctx->prev.x >= ctx->box[0].x) << 1) | (x >= ctx->box[0].x);
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}
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static enum path_transition
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path_transition_right_edge(struct clip_context *ctx, float x, float y)
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{
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return ((ctx->prev.x < ctx->box[1].x) << 1) | (x < ctx->box[1].x);
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}
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static enum path_transition
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path_transition_top_edge(struct clip_context *ctx, float x, float y)
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{
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return ((ctx->prev.y >= ctx->box[0].y) << 1) | (y >= ctx->box[0].y);
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}
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static enum path_transition
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path_transition_bottom_edge(struct clip_context *ctx, float x, float y)
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{
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return ((ctx->prev.y < ctx->box[1].y) << 1) | (y < ctx->box[1].y);
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}
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static void
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clip_polygon_leftright(struct clip_context *ctx,
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enum path_transition transition,
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float x, float y, float clip_x)
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{
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float yi;
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switch (transition) {
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case PATH_TRANSITION_IN_TO_IN:
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clip_append_vertex(ctx, x, y);
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break;
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case PATH_TRANSITION_IN_TO_OUT:
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yi = clip_intersect_y(ctx->prev.x, ctx->prev.y, x, y, clip_x);
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clip_append_vertex(ctx, clip_x, yi);
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break;
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case PATH_TRANSITION_OUT_TO_IN:
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yi = clip_intersect_y(ctx->prev.x, ctx->prev.y, x, y, clip_x);
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clip_append_vertex(ctx, clip_x, yi);
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clip_append_vertex(ctx, x, y);
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break;
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case PATH_TRANSITION_OUT_TO_OUT:
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/* nothing */
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break;
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default:
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assert(0 && "bad enum path_transition");
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}
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ctx->prev.x = x;
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ctx->prev.y = y;
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}
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static void
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clip_polygon_topbottom(struct clip_context *ctx,
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enum path_transition transition,
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float x, float y, float clip_y)
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{
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float xi;
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switch (transition) {
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case PATH_TRANSITION_IN_TO_IN:
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clip_append_vertex(ctx, x, y);
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break;
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case PATH_TRANSITION_IN_TO_OUT:
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xi = clip_intersect_x(ctx->prev.x, ctx->prev.y, x, y, clip_y);
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clip_append_vertex(ctx, xi, clip_y);
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break;
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case PATH_TRANSITION_OUT_TO_IN:
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xi = clip_intersect_x(ctx->prev.x, ctx->prev.y, x, y, clip_y);
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clip_append_vertex(ctx, xi, clip_y);
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clip_append_vertex(ctx, x, y);
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break;
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case PATH_TRANSITION_OUT_TO_OUT:
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/* nothing */
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break;
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default:
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assert(0 && "bad enum path_transition");
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}
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ctx->prev.x = x;
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ctx->prev.y = y;
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}
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struct polygon8 {
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struct clipper_vertex pos[8];
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int n;
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};
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static void
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clip_context_prepare(struct clip_context *ctx, const struct polygon8 *src,
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struct clipper_vertex *dst)
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{
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ctx->prev.x = src->pos[src->n - 1].x;
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ctx->prev.y = src->pos[src->n - 1].y;
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ctx->vertices = dst;
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}
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static int
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clip_polygon_left(struct clip_context *ctx, const struct polygon8 *src,
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struct clipper_vertex *dst)
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{
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enum path_transition trans;
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int i;
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if (src->n < 2)
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return 0;
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clip_context_prepare(ctx, src, dst);
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for (i = 0; i < src->n; i++) {
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trans = path_transition_left_edge(ctx, src->pos[i].x, src->pos[i].y);
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clip_polygon_leftright(ctx, trans, src->pos[i].x, src->pos[i].y,
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ctx->box[0].x);
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}
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return ctx->vertices - dst;
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}
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static int
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clip_polygon_right(struct clip_context *ctx, const struct polygon8 *src,
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struct clipper_vertex *dst)
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{
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enum path_transition trans;
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int i;
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if (src->n < 2)
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return 0;
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clip_context_prepare(ctx, src, dst);
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for (i = 0; i < src->n; i++) {
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trans = path_transition_right_edge(ctx, src->pos[i].x, src->pos[i].y);
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clip_polygon_leftright(ctx, trans, src->pos[i].x, src->pos[i].y,
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ctx->box[1].x);
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}
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return ctx->vertices - dst;
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}
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static int
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clip_polygon_top(struct clip_context *ctx, const struct polygon8 *src,
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struct clipper_vertex *dst)
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{
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enum path_transition trans;
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int i;
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if (src->n < 2)
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return 0;
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clip_context_prepare(ctx, src, dst);
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for (i = 0; i < src->n; i++) {
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trans = path_transition_top_edge(ctx, src->pos[i].x, src->pos[i].y);
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clip_polygon_topbottom(ctx, trans, src->pos[i].x, src->pos[i].y,
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ctx->box[0].y);
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}
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return ctx->vertices - dst;
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}
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static int
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clip_polygon_bottom(struct clip_context *ctx, const struct polygon8 *src,
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struct clipper_vertex *dst)
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{
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enum path_transition trans;
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int i;
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if (src->n < 2)
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return 0;
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clip_context_prepare(ctx, src, dst);
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for (i = 0; i < src->n; i++) {
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trans = path_transition_bottom_edge(ctx, src->pos[i].x, src->pos[i].y);
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clip_polygon_topbottom(ctx, trans, src->pos[i].x, src->pos[i].y,
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ctx->box[1].y);
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}
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return ctx->vertices - dst;
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}
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/* General purpose polygon clipping algorithm based on Sutherland-Hodgman:
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* https://www.codeguru.com/cplusplus/polygon-clipping/
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*/
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WESTON_EXPORT_FOR_TESTS int
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clipper_clip(const struct clipper_vertex *polygon,
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size_t polygon_len,
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const struct clipper_vertex box[2],
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struct clipper_vertex *restrict vertices)
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{
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struct clip_context ctx;
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struct polygon8 p, tmp;
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int i, n;
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if (polygon_len > 8)
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return -1;
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memcpy(ctx.box, box, 2 * sizeof *box);
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memcpy(p.pos, polygon, polygon_len * sizeof *polygon);
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p.n = polygon_len;
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tmp.n = clip_polygon_left(&ctx, &p, tmp.pos);
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p.n = clip_polygon_right(&ctx, &tmp, p.pos);
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tmp.n = clip_polygon_top(&ctx, &p, tmp.pos);
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p.n = clip_polygon_bottom(&ctx, &tmp, p.pos);
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/* Get rid of duplicate vertices */
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vertices[0] = p.pos[0];
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n = 1;
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for (i = 1; i < p.n; i++) {
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if (clipper_float_difference(vertices[n - 1].x, p.pos[i].x) == 0.0f &&
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clipper_float_difference(vertices[n - 1].y, p.pos[i].y) == 0.0f)
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continue;
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vertices[n] = p.pos[i];
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n++;
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}
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if (clipper_float_difference(vertices[n - 1].x, p.pos[0].x) == 0.0f &&
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clipper_float_difference(vertices[n - 1].y, p.pos[0].y) == 0.0f)
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n--;
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return n;
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}
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void
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clipper_quad_init(struct clipper_quad *quad,
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const struct clipper_vertex polygon[4],
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bool axis_aligned)
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{
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int i;
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memcpy(quad->polygon, polygon, 4 * sizeof *polygon);
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quad->axis_aligned = axis_aligned;
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if (axis_aligned)
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return;
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/* Find axis-aligned bounding box. */
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quad->bbox[0].x = quad->bbox[1].x = polygon[0].x;
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quad->bbox[0].y = quad->bbox[1].y = polygon[0].y;
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for (i = 1; i < 4; i++) {
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quad->bbox[0].x = MIN(quad->bbox[0].x, polygon[i].x);
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quad->bbox[1].x = MAX(quad->bbox[1].x, polygon[i].x);
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quad->bbox[0].y = MIN(quad->bbox[0].y, polygon[i].y);
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quad->bbox[1].y = MAX(quad->bbox[1].y, polygon[i].y);
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}
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}
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int
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clipper_quad_clip(struct clipper_quad *quad,
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const struct clipper_vertex box[2],
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struct clipper_vertex *restrict vertices)
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{
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int i, n;
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/* Aligned case: quad edges are parallel to clipping box edges, there
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* will be either four or zero edges. We just need to clamp the quad
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* edges to the clipping box edges and test for non-zero area:
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*/
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if (quad->axis_aligned) {
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for (i = 0; i < 4; i++) {
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vertices[i].x = CLIP(quad->polygon[i].x,
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box[0].x, box[1].x);
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vertices[i].y = CLIP(quad->polygon[i].y,
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box[0].y, box[1].y);
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}
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if ((vertices[0].x != vertices[1].x) &&
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(vertices[0].y != vertices[2].y))
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return 4;
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else
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return 0;
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}
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/* Unaligned case: first, simple bounding box check to discard early a
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* quad that does not intersect with the clipping box:
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*/
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if ((quad->bbox[0].x >= box[1].x) || (quad->bbox[1].x <= box[0].x) ||
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(quad->bbox[0].y >= box[1].y) || (quad->bbox[1].y <= box[0].y))
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return 0;
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/* Then use our general purpose clipping algorithm:
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*/
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n = clipper_clip(quad->polygon, 4, box, vertices);
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if (n < 3)
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return 0;
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return n;
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}
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int
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clipper_quad_clip_box32(struct clipper_quad *quad,
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const struct pixman_box32 *box,
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struct clipper_vertex *restrict vertices)
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{
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struct clipper_vertex box_vertices[2] = {
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{ box->x1, box->y1 },
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{ box->x2, box->y2 }
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};
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return clipper_quad_clip(quad, box_vertices, vertices);
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}
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