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Merge pull request #100 from yamt/flood-fill2

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Improve stack usage for flood filling
This commit is contained in:
Daniel Beer 2021-05-12 10:30:49 +12:00 committed by GitHub
commit 5adb7597c1
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GPG key ID: 4AEE18F83AFDEB23
3 changed files with 186 additions and 27 deletions
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167
lib/identify.c
View file

@ -16,6 +16,7 @@
#include <limits.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>
#include <math.h>
#include "quirc_internal.h"
@ -122,21 +123,23 @@ static void perspective_unmap(const double *c,
* Span-based floodfill routine
*/
#define FLOOD_FILL_MAX_DEPTH 4096
typedef void (*span_func_t)(void *user_data, int y, int left, int right);
static void flood_fill_seed(struct quirc *q, int x, int y, int from, int to,
static void flood_fill_line(struct quirc *q, int x, int y,
int from, int to,
span_func_t func, void *user_data,
int depth)
int *leftp, int *rightp)
{
int left = x;
int right = x;
quirc_pixel_t *row;
int left;
int right;
int i;
quirc_pixel_t *row = q->pixels + y * q->w;
if (depth >= FLOOD_FILL_MAX_DEPTH)
return;
row = q->pixels + y * q->w;
QUIRC_ASSERT(row[x] == from);
left = x;
right = x;
while (left > 0 && row[left - 1] == from)
left--;
@ -148,26 +151,132 @@ static void flood_fill_seed(struct quirc *q, int x, int y, int from, int to,
for (i = left; i <= right; i++)
row[i] = to;
/* Return the processed range */
*leftp = left;
*rightp = right;
if (func)
func(user_data, y, left, right);
/* Seed new flood-fills */
if (y > 0) {
row = q->pixels + (y - 1) * q->w;
for (i = left; i <= right; i++)
if (row[i] == from)
flood_fill_seed(q, i, y - 1, from, to,
func, user_data, depth + 1);
}
if (y < q->h - 1) {
row = q->pixels + (y + 1) * q->w;
static struct quirc_flood_fill_vars *flood_fill_call_next(
struct quirc *q,
quirc_pixel_t *row,
int from, int to,
span_func_t func, void *user_data,
struct quirc_flood_fill_vars *vars,
int direction)
{
int *leftp;
for (i = left; i <= right; i++)
if (row[i] == from)
flood_fill_seed(q, i, y + 1, from, to,
func, user_data, depth + 1);
if (direction < 0) {
leftp = &vars->left_up;
} else {
leftp = &vars->left_down;
}
while (*leftp <= vars->right) {
if (row[*leftp] == from) {
struct quirc_flood_fill_vars *next_vars;
int next_left;
/* Set up the next context */
next_vars = vars + 1;
next_vars->y = vars->y + direction;
/* Fill the extent */
flood_fill_line(q,
*leftp,
next_vars->y,
from, to,
func, user_data,
&next_left,
&next_vars->right);
next_vars->left_down = next_left;
next_vars->left_up = next_left;
return next_vars;
}
(*leftp)++;
}
return NULL;
}
static void flood_fill_seed(struct quirc *q,
int x0, int y0,
int from, int to,
span_func_t func, void *user_data)
{
struct quirc_flood_fill_vars *const stack = q->flood_fill_vars;
const size_t stack_size = q->num_flood_fill_vars;
const struct quirc_flood_fill_vars *const last_vars =
&stack[stack_size - 1];
QUIRC_ASSERT(from != to);
QUIRC_ASSERT(q->pixels[y0 * q->w + x0] == from);
struct quirc_flood_fill_vars *next_vars;
int next_left;
/* Set up the first context */
next_vars = stack;
next_vars->y = y0;
/* Fill the extent */
flood_fill_line(q, x0, next_vars->y, from, to,
func, user_data,
&next_left, &next_vars->right);
next_vars->left_down = next_left;
next_vars->left_up = next_left;
while (true) {
struct quirc_flood_fill_vars * const vars = next_vars;
quirc_pixel_t *row;
if (vars == last_vars) {
/*
* "Stack overflow".
* Just stop and return.
* This can be caused by very complex shapes in
* the image, which is not likely a part of
* a valid QR code anyway.
*/
break;
}
/* Seed new flood-fills */
if (vars->y > 0) {
row = q->pixels + (vars->y - 1) * q->w;
next_vars = flood_fill_call_next(q, row,
from, to,
func, user_data,
vars, -1);
if (next_vars != NULL) {
continue;
}
}
if (vars->y < q->h - 1) {
row = q->pixels + (vars->y + 1) * q->w;
next_vars = flood_fill_call_next(q, row,
from, to,
func, user_data,
vars, 1);
if (next_vars != NULL) {
continue;
}
}
if (vars > stack) {
/* Restore the previous context */
next_vars = vars - 1;
continue;
}
/* We've done. */
break;
}
}
@ -260,7 +369,7 @@ static int region_code(struct quirc *q, int x, int y)
box->seed.y = y;
box->capstone = -1;
flood_fill_seed(q, x, y, pixel, region, area_count, box, 0);
flood_fill_seed(q, x, y, pixel, region, area_count, box);
return region;
}
@ -330,7 +439,7 @@ static void find_region_corners(struct quirc *q,
psd.scores[0] = -1;
flood_fill_seed(q, region->seed.x, region->seed.y,
rcode, QUIRC_PIXEL_BLACK,
find_one_corner, &psd, 0);
find_one_corner, &psd);
psd.ref.x = psd.corners[0].x - psd.ref.x;
psd.ref.y = psd.corners[0].y - psd.ref.y;
@ -348,7 +457,7 @@ static void find_region_corners(struct quirc *q,
flood_fill_seed(q, region->seed.x, region->seed.y,
QUIRC_PIXEL_BLACK, rcode,
find_other_corners, &psd, 0);
find_other_corners, &psd);
}
static void record_capstone(struct quirc *q, int ring, int stone)
@ -966,10 +1075,10 @@ static void record_qr_grid(struct quirc *q, int a, int b, int c)
flood_fill_seed(q, reg->seed.x, reg->seed.y,
qr->align_region, QUIRC_PIXEL_BLACK,
NULL, NULL, 0);
NULL, NULL);
flood_fill_seed(q, reg->seed.x, reg->seed.y,
QUIRC_PIXEL_BLACK, qr->align_region,
find_leftmost_to_line, &psd, 0);
find_leftmost_to_line, &psd);
}
}

35
lib/quirc.c
View file

@ -41,6 +41,7 @@ void quirc_destroy(struct quirc *q)
same size, so we need to be careful here to avoid a double free */
if (!QUIRC_PIXEL_ALIAS_IMAGE)
free(q->pixels);
free(q->flood_fill_vars);
free(q);
}
@ -48,6 +49,9 @@ int quirc_resize(struct quirc *q, int w, int h)
{
uint8_t *image = NULL;
quirc_pixel_t *pixels = NULL;
size_t num_vars;
size_t vars_byte_size;
struct quirc_flood_fill_vars *vars = NULL;
/*
* XXX: w and h should be size_t (or at least unsigned) as negatives
@ -86,6 +90,33 @@ int quirc_resize(struct quirc *q, int w, int h)
goto fail;
}
/*
* alloc the work area for the flood filling logic.
*
* the size was chosen with the following assumptions and observations:
*
* - rings are the regions which requires the biggest work area.
* - they consumes the most when they are rotated by about 45 degree.
* in that case, the necessary depth is about (2 * height_of_the_ring).
* - the maximum height of rings would be about 1/3 of the image height.
*/
if ((size_t)h * 2 / 2 != h) {
goto fail; /* size_t overflow */
}
num_vars = (size_t)h * 2 / 3;
if (num_vars == 0) {
num_vars = 1;
}
vars_byte_size = sizeof(*vars) * num_vars;
if (vars_byte_size / sizeof(*vars) != num_vars) {
goto fail; /* size_t overflow */
}
vars = malloc(vars_byte_size);
if (!vars)
goto fail;
/* alloc succeeded, update `q` with the new size and buffers */
q->w = w;
q->h = h;
@ -95,12 +126,16 @@ int quirc_resize(struct quirc *q, int w, int h)
free(q->pixels);
q->pixels = pixels;
}
free(q->flood_fill_vars);
q->flood_fill_vars = vars;
q->num_flood_fill_vars = num_vars;
return 0;
/* NOTREACHED */
fail:
free(image);
free(pixels);
free(vars);
return -1;
}

15
lib/quirc_internal.h
View file

@ -17,8 +17,13 @@
#ifndef QUIRC_INTERNAL_H_
#define QUIRC_INTERNAL_H_
#include <assert.h>
#include <stdlib.h>
#include "quirc.h"
#define QUIRC_ASSERT(a) assert(a)
#define QUIRC_PIXEL_WHITE 0
#define QUIRC_PIXEL_BLACK 1
#define QUIRC_PIXEL_REGION 2
@ -75,6 +80,13 @@ struct quirc_grid {
double c[QUIRC_PERSPECTIVE_PARAMS];
};
struct quirc_flood_fill_vars {
int y;
int right;
int left_up;
int left_down;
};
struct quirc {
uint8_t *image;
quirc_pixel_t *pixels;
@ -89,6 +101,9 @@ struct quirc {
int num_grids;
struct quirc_grid grids[QUIRC_MAX_GRIDS];
size_t num_flood_fill_vars;
struct quirc_flood_fill_vars *flood_fill_vars;
};
/************************************************************************