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ultimatepp/bazaar/PixRaster/lib/maze.c
micio db3a6a0036 Start of Leptonica library support 
git-svn-id: svn://ultimatepp.org/upp/trunk@1554 f0d560ea-af0d-0410-9eb7-867de7ffcac7
2009-09-06 15:49:56 +00:00

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/*====================================================================*
- Copyright (C) 2001 Leptonica. All rights reserved.
- This software is distributed in the hope that it will be
- useful, but with NO WARRANTY OF ANY KIND.
- No author or distributor accepts responsibility to anyone for the
- consequences of using this software, or for whether it serves any
- particular purpose or works at all, unless he or she says so in
- writing. Everyone is granted permission to copy, modify and
- redistribute this source code, for commercial or non-commercial
- purposes, with the following restrictions: (1) the origin of this
- source code must not be misrepresented; (2) modified versions must
- be plainly marked as such; and (3) this notice may not be removed
- or altered from any source or modified source distribution.
*====================================================================*/
/*
* maze.c
*
* This is a game with a pedagogical slant. A maze is represented
* by a binary image. The ON pixels (fg) are walls. The goal is
* to navigate on OFF pixels (bg), using Manhattan steps
* (N, S, E, W), between arbitrary start and end positions.
* The problem is thus to find the shortest route between two points
* in a binary image that are 4-connected in the bg. This is done
* with a breadth-first search, implemented with a queue.
* We also use a queue of pointers to generate the maze (image).
*
* PIX *generateBinaryMaze()
* static MAZEEL *mazeelCreate()
*
* PIX *pixSearchBinaryMaze()
* static l_int32 localSearchForBackground()
*
* Generalizing a maze to a grayscale image, the search is
* now for the "shortest" or least cost path, for some given
* cost function.
*
* PIX *pixSearchGrayMaze()
*
* Display functions
* PIX *pixDisplayPta()
* PIX *pixDisplayPtaa()
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "allheaders.h"
static const l_int32 MIN_MAZE_WIDTH = 50;
static const l_int32 MIN_MAZE_HEIGHT = 50;
static const l_float32 DEFAULT_WALL_PROBABILITY = 0.65;
static const l_float32 DEFAULT_ANISOTROPY_RATIO = 0.25;
enum { /* direction from parent to newly created element */
START_LOC = 0,
DIR_NORTH = 1,
DIR_SOUTH = 2,
DIR_WEST = 3,
DIR_EAST = 4
};
struct MazeElement {
l_float32 distance;
l_int32 x;
l_int32 y;
l_uint32 val; /* value of maze pixel at this location */
l_int32 dir; /* direction from parent to child */
};
typedef struct MazeElement MAZEEL;
static MAZEEL *mazeelCreate(l_int32 x, l_int32 y, l_int32 dir);
static l_int32 localSearchForBackground(PIX *pix, l_int32 *px,
l_int32 *py, l_int32 maxrad);
#ifndef NO_CONSOLE_IO
#define DEBUG_PATH 0
#define DEBUG_MAZE 0
#endif /* ~NO_CONSOLE_IO */
/*---------------------------------------------------------------------*
* Binary maze generation as cellular automaton *
*---------------------------------------------------------------------*/
/*!
* generateBinaryMaze()
*
* Input: w, h (size of maze)
* xi, yi (initial location)
* wallps (probability that a pixel to the side is ON)
* ranis (ratio of prob that pixel in forward direction
* is a wall to the probability that pixel in
* side directions is a wall)
* Return: pix, or null on error
*
* Notes:
* (1) We have two input probability factors that determine the
* density of walls and average length of straight passages.
* When ranis < 1.0, you are more likely to generate a wall
* to the side than going forward. Enter 0.0 for either if
* you want to use the default values.
* (2) This is a type of percolation problem, and exhibits
* different phases for different parameters wallps and ranis.
* For larger values of these parameters, regions in the maze
* are not explored because the maze generator walls them
* off and cannot get through. The boundary between the
* two phases in this two-dimensional parameter space goes
* near these values:
* wallps ranis
* 0.35 1.00
* 0.40 0.85
* 0.45 0.70
* 0.50 0.50
* 0.55 0.40
* 0.60 0.30
* 0.65 0.25
* 0.70 0.19
* 0.75 0.15
* 0.80 0.11
* (3) Because here is a considerable amount of overhead in calling
* pixGetPixel() and pixSetPixel(), this function can be sped
* up with little effort using raster line pointers and the
* GET_DATA* and SET_DATA* macros.
*/
PIX *
generateBinaryMaze(l_int32 w,
l_int32 h,
l_int32 xi,
l_int32 yi,
l_float32 wallps,
l_float32 ranis)
{
l_int32 x, y, dir;
l_uint32 val;
l_float32 frand, wallpf, testp;
MAZEEL *el, *elp;
PIX *pixd; /* the destination maze */
PIX *pixm; /* for bookkeeping, to indicate pixels already visited */
L_QUEUE *lq;
if (w < MIN_MAZE_WIDTH)
w = MIN_MAZE_WIDTH;
if (h < MIN_MAZE_HEIGHT)
h = MIN_MAZE_HEIGHT;
if (xi <= 0 || xi >= w)
xi = w / 6;
if (yi <= 0 || yi >= h)
yi = h / 5;
if (wallps < 0.05 || wallps > 0.95)
wallps = DEFAULT_WALL_PROBABILITY;
if (ranis < 0.05 || ranis > 1.0)
ranis = DEFAULT_ANISOTROPY_RATIO;
wallpf = wallps * ranis;
#if DEBUG_MAZE
fprintf(stderr, "(w, h) = (%d, %d), (xi, yi) = (%d, %d)\n", w, h, xi, yi);
fprintf(stderr, "Using: prob(wall) = %7.4f, anisotropy factor = %7.4f\n",
wallps, ranis);
#endif /* DEBUG_MAZE */
/* these are initialized to OFF */
pixd = pixCreate(w, h, 1);
pixm = pixCreate(w, h, 1);
lq = lqueueCreate(0);
/* prime the queue with the first pixel; it is OFF */
el = mazeelCreate(xi, yi, START_LOC);
pixSetPixel(pixm, xi, yi, 1); /* mark visited */
lqueueAdd(lq, el);
/* while we're at it ... */
while (lqueueGetCount(lq) > 0) {
elp = (MAZEEL *)lqueueRemove(lq);
x = elp->x;
y = elp->y;
dir = elp->dir;
if (x > 0) { /* check west */
pixGetPixel(pixm, x - 1, y, &val);
if (val == 0) { /* not yet visited */
pixSetPixel(pixm, x - 1, y, 1); /* mark visited */
frand = (l_float32)rand() / (l_float32)RAND_MAX;
testp = wallps;
if (dir == DIR_WEST)
testp = wallpf;
if (frand <= testp) { /* make it a wall */
pixSetPixel(pixd, x - 1, y, 1);
}
else { /* not a wall */
el = mazeelCreate(x - 1, y, DIR_WEST);
lqueueAdd(lq, el);
}
}
}
if (y > 0) { /* check north */
pixGetPixel(pixm, x, y - 1, &val);
if (val == 0) { /* not yet visited */
pixSetPixel(pixm, x, y - 1, 1); /* mark visited */
frand = (l_float32)rand() / (l_float32)RAND_MAX;
testp = wallps;
if (dir == DIR_NORTH)
testp = wallpf;
if (frand <= testp) { /* make it a wall */
pixSetPixel(pixd, x, y - 1, 1);
}
else { /* not a wall */
el = mazeelCreate(x, y - 1, DIR_NORTH);
lqueueAdd(lq, el);
}
}
}
if (x < w - 1) { /* check east */
pixGetPixel(pixm, x + 1, y, &val);
if (val == 0) { /* not yet visited */
pixSetPixel(pixm, x + 1, y, 1); /* mark visited */
frand = (l_float32)rand() / (l_float32)RAND_MAX;
testp = wallps;
if (dir == DIR_EAST)
testp = wallpf;
if (frand <= testp) { /* make it a wall */
pixSetPixel(pixd, x + 1, y, 1);
}
else { /* not a wall */
el = mazeelCreate(x + 1, y, DIR_EAST);
lqueueAdd(lq, el);
}
}
}
if (y < h - 1) { /* check south */
pixGetPixel(pixm, x, y + 1, &val);
if (val == 0) { /* not yet visited */
pixSetPixel(pixm, x, y + 1, 1); /* mark visited */
frand = (l_float32)rand() / (l_float32)RAND_MAX;
testp = wallps;
if (dir == DIR_SOUTH)
testp = wallpf;
if (frand <= testp) { /* make it a wall */
pixSetPixel(pixd, x, y + 1, 1);
}
else { /* not a wall */
el = mazeelCreate(x, y + 1, DIR_SOUTH);
lqueueAdd(lq, el);
}
}
}
FREE(elp);
}
lqueueDestroy(&lq, TRUE);
pixDestroy(&pixm);
return pixd;
}
static MAZEEL *
mazeelCreate(l_int32 x,
l_int32 y,
l_int32 dir)
{
MAZEEL *el;
el = (MAZEEL *)CALLOC(1, sizeof(MAZEEL));
el->x = x;
el->y = y;
el->dir = dir;
return el;
}
/*---------------------------------------------------------------------*
* Binary maze search *
*---------------------------------------------------------------------*/
/*!
* pixSearchBinaryMaze()
*
* Input: pixs (1 bpp, maze)
* xi, yi (beginning point; use same initial point
* that was used to generate the maze)
* xf, yf (end point, or close to it)
* &ppixd (<optional return> maze with path illustrated, or
* if no path possible, the part of the maze
* that was searched)
* Return: pta (shortest path), or null if either no path
* exists or on error
*
* Note: Because here is a considerable amount of overhead in calling
* pixGetPixel() and pixSetPixel(), this function can be sped
* up with little effort using raster line pointers and the
* GET_DATA* and SET_DATA* macros.
*
* Commentary:
* The goal is to find the shortest path between beginning and
* end points, without going through walls, and there are many
* ways to solve this problem.
*
* We use a queue to implement a breadth-first search. Two auxiliary
* "image" data structures can be used: one to mark the visited
* pixels and one to give the direction to the parent for each
* visited pixels. The first structure is used to avoid putting
* pixels on the queue more than once, and the second is used
* for retracing back to the origin, like the breadcrumbs in
* Hansel and Gretel. Each pixel taken off the queue is destroyed
* after it is used to locate the allowed neighbors. In fact,
* only one distance image is required, if you initialize it
* to some value that signifies "not yet visited." (We use
* a binary image for marking visited pixels because it is clearer.)
* This method for a simple search of a binary maze is implemented in
* searchBinaryMaze().
*
* An alternative method would store the (manhattan) distance from
* the start point with each pixel on the queue. The children
* of each pixel get a distance one larger than the parent. These
* values can be stored in an auxiliary distance map image
* that is constructed simultaneously with the search. Once the
* end point is reached, the distance map is used to backtrack
* along a minimum path. There may be several equal length
* minimum paths, any one of which can be chosen this way.
*
*/
PTA *
pixSearchBinaryMaze(PIX *pixs,
l_int32 xi,
l_int32 yi,
l_int32 xf,
l_int32 yf,
PIX **ppixd)
{
l_int32 i, j, x, y, w, h, d, found;
l_uint32 val, rpixel, gpixel, bpixel;
void **lines1, **linem1, **linep8, **lined32;
MAZEEL *el, *elp;
PIX *pixd; /* the shortest path written on the maze image */
PIX *pixm; /* for bookkeeping, to indicate pixels already visited */
PIX *pixp; /* for bookkeeping, to indicate direction to parent */
L_QUEUE *lq;
PTA *pta;
PROCNAME("pixSearchBinaryMaze");
if (ppixd) *ppixd = NULL;
if (!pixs)
return (PTA *)ERROR_PTR("pixs not defined", procName, NULL);
pixGetDimensions(pixs, &w, &h, &d);
if (d != 1)
return (PTA *)ERROR_PTR("pixs not 1 bpp", procName, NULL);
if (xi <= 0 || xi >= w)
return (PTA *)ERROR_PTR("xi not valid", procName, NULL);
if (yi <= 0 || yi >= h)
return (PTA *)ERROR_PTR("yi not valid", procName, NULL);
pixGetPixel(pixs, xi, yi, &val);
if (val != 0)
return (PTA *)ERROR_PTR("(xi,yi) not bg pixel", procName, NULL);
pixd = NULL;
pta = NULL;
/* find a bg pixel near input point (xf, yf) */
localSearchForBackground(pixs, &xf, &yf, 5);
#if DEBUG_MAZE
fprintf(stderr, "(xi, yi) = (%d, %d), (xf, yf) = (%d, %d)\n",
xi, yi, xf, yf);
#endif /* DEBUG_MAZE */
pixm = pixCreate(w, h, 1); /* initialized to OFF */
pixp = pixCreate(w, h, 8); /* direction to parent stored as enum val */
lines1 = pixGetLinePtrs(pixs, NULL);
linem1 = pixGetLinePtrs(pixm, NULL);
linep8 = pixGetLinePtrs(pixp, NULL);
lq = lqueueCreate(0);
/* prime the queue with the first pixel; it is OFF */
el = mazeelCreate(xi, yi, 0); /* don't need direction here */
pixSetPixel(pixm, xi, yi, 1); /* mark visited */
lqueueAdd(lq, el);
/* fill up the pix storing directions to parents,
* stopping when we hit the point (xf, yf) */
found = FALSE;
while (lqueueGetCount(lq) > 0) {
elp = (MAZEEL *)lqueueRemove(lq);
x = elp->x;
y = elp->y;
if (x == xf && y == yf) {
found = TRUE;
FREE(elp);
break;
}
if (x > 0) { /* check to west */
val = GET_DATA_BIT(linem1[y], x - 1);
if (val == 0) { /* not yet visited */
SET_DATA_BIT(linem1[y], x - 1); /* mark visited */
val = GET_DATA_BIT(lines1[y], x - 1);
if (val == 0) { /* bg, not a wall */
SET_DATA_BYTE(linep8[y], x - 1, DIR_EAST); /* parent E */
el = mazeelCreate(x - 1, y, 0);
lqueueAdd(lq, el);
}
}
}
if (y > 0) { /* check north */
val = GET_DATA_BIT(linem1[y - 1], x);
if (val == 0) { /* not yet visited */
SET_DATA_BIT(linem1[y - 1], x); /* mark visited */
val = GET_DATA_BIT(lines1[y - 1], x);
if (val == 0) { /* bg, not a wall */
SET_DATA_BYTE(linep8[y - 1], x, DIR_SOUTH); /* parent S */
el = mazeelCreate(x, y - 1, 0);
lqueueAdd(lq, el);
}
}
}
if (x < w - 1) { /* check east */
val = GET_DATA_BIT(linem1[y], x + 1);
if (val == 0) { /* not yet visited */
SET_DATA_BIT(linem1[y], x + 1); /* mark visited */
val = GET_DATA_BIT(lines1[y], x + 1);
if (val == 0) { /* bg, not a wall */
SET_DATA_BYTE(linep8[y], x + 1, DIR_WEST); /* parent W */
el = mazeelCreate(x + 1, y, 0);
lqueueAdd(lq, el);
}
}
}
if (y < h - 1) { /* check south */
val = GET_DATA_BIT(linem1[y + 1], x);
if (val == 0) { /* not yet visited */
SET_DATA_BIT(linem1[y + 1], x); /* mark visited */
val = GET_DATA_BIT(lines1[y + 1], x);
if (val == 0) { /* bg, not a wall */
SET_DATA_BYTE(linep8[y + 1], x, DIR_NORTH); /* parent N */
el = mazeelCreate(x, y + 1, 0);
lqueueAdd(lq, el);
}
}
}
FREE(elp);
}
lqueueDestroy(&lq, TRUE);
pixDestroy(&pixm);
FREE(linem1);
if (ppixd) {
pixd = pixUnpackBinary(pixs, 32, 1);
*ppixd = pixd;
}
composeRGBPixel(255, 0, 0, &rpixel); /* start point */
composeRGBPixel(0, 255, 0, &gpixel);
composeRGBPixel(0, 0, 255, &bpixel); /* end point */
if (!found) {
L_INFO(" No path found", procName);
if (pixd) { /* paint all visited locations */
lined32 = pixGetLinePtrs(pixd, NULL);
for (i = 0; i < h; i++) {
for (j = 0; j < w; j++) {
val = GET_DATA_BYTE(linep8[i], j);
if (val != 0 && pixd)
SET_DATA_FOUR_BYTES(lined32[i], j, gpixel);
}
}
FREE(lined32);
}
}
else { /* write path onto pixd */
L_INFO(" Path found", procName);
pta = ptaCreate(0);
x = xf;
y = yf;
while (1) {
ptaAddPt(pta, x, y);
if (x == xi && y == yi)
break;
if (pixd)
pixSetPixel(pixd, x, y, gpixel);
pixGetPixel(pixp, x, y, &val);
if (val == DIR_NORTH)
y--;
else if (val == DIR_SOUTH)
y++;
else if (val == DIR_EAST)
x++;
else if (val == DIR_WEST)
x--;
}
}
if (pixd) {
pixSetPixel(pixd, xi, yi, rpixel);
pixSetPixel(pixd, xf, yf, bpixel);
}
pixDestroy(&pixp);
FREE(lines1);
FREE(linep8);
return pta;
}
/*!
* localSearchForBackground()
*
* Input: &x, &y (starting position for search; return found position)
* maxrad (max distance to search from starting location)
* Return: 0 if bg pixel found; 1 if not found
*/
static l_int32
localSearchForBackground(PIX *pix,
l_int32 *px,
l_int32 *py,
l_int32 maxrad)
{
l_int32 x, y, w, h, r, i, j;
l_uint32 val;
x = *px;
y = *py;
pixGetPixel(pix, x, y, &val);
if (val == 0) return 0;
/* For each value of r, restrict the search to the boundary
* pixels in a square centered on (x,y), clipping to the
* image boundaries if necessary. */
pixGetDimensions(pix, &w, &h, NULL);
for (r = 1; r < maxrad; r++) {
for (i = -r; i <= r; i++) {
if (y + i < 0 || y + i >= h)
continue;
for (j = -r; j <= r; j++) {
if (x + j < 0 || x + j >= w)
continue;
if (L_ABS(i) != r && L_ABS(j) != r) /* not on "r ring" */
continue;
pixGetPixel(pix, x + j, y + i, &val);
if (val == 0) {
*px = x + j;
*py = y + i;
return 0;
}
}
}
}
return 1;
}
/*---------------------------------------------------------------------*
* Gray maze search *
*---------------------------------------------------------------------*/
/*!
* pixSearchGrayMaze()
*
* Input: pixs (1 bpp, maze)
* xi, yi (beginning point; use same initial point
* that was used to generate the maze)
* xf, yf (end point, or close to it)
* &ppixd (<optional return> maze with path illustrated, or
* if no path possible, the part of the maze
* that was searched)
* Return: pta (shortest path), or null if either no path
* exists or on error
*
* Commentary:
* Consider first a slight generalization of the binary maze
* search problem. Suppose that you can go through walls,
* but the cost is higher (say, an increment of 3 to go into
* a wall pixel rather than 1)? You're still trying to find
* the shortest path. One way to do this is with an ordered
* queue, and a simple way to visualize an ordered queue is as
* a set of stacks, each stack being marked with the distance
* of each pixel in the stack from the start. We place the
* start pixel in stack 0, pop it, and process its 4 children.
* Each pixel is given a distance that is incremented from that
* of its parent (0 in this case), depending on if it is a wall
* pixel or not. That value may be recorded on a distance map,
* according to the algorithm below. For children of the first
* pixel, those not on a wall go in stack 1, and wall
* children go in stack 3. Stack 0 being emptied, the process
* then continues with pixels being popped from stack 1.
* Here is the algorithm for each child pixel. The pixel's
* distance value, were it to be placed on a stack, is compared
* with the value for it that is on the distance map. There
* are three possible cases:
* (1) If the pixel has not yet been registered, it is pushed
* on its stack and the distance is written to the map.
* (2) If it has previously been registered with a higher distance,
* the distance on the map is relaxed to that of the
* current pixel, which is then placed on its stack.
* (3) If it has previously been registered with an equal
* or lower value, the pixel is discarded.
* The pixels are popped and processed successively from
* stack 1, and when stack 1 is empty, popping starts on stack 2.
* This continues until the destination pixel is popped off
* a stack. The minimum path is then derived from the distance map,
* going back from the end point as before. This is just Dijkstra's
* algorithm for a directed graph; here, the underlying graph
* (consisting of the pixels and four edges connecting each pixel
* to its 4-neighbor) is a special case of a directed graph, where
* each edge is bi-directional. The implementation of this generalized
* maze search is left as an exercise to the reader.
*
* Let's generalize a bit further. Suppose the "maze" is just
* a grayscale image -- think of it as an elevation map. The cost
* of moving on this surface depends on the height, or the gradient,
* or whatever you want. All that is required is that the cost
* is specified and non-negative on each link between adjacent
* pixels. Now the problem becomes: find the least cost path
* moving on this surface between two specified end points.
* For example, if the cost across an edge between two pixels
* depends on the "gradient", you can use:
* cost = 1 + L_ABS(deltaV)
* where deltaV is the difference in value between two adjacent
* pixels. If the costs are all integers, we can still use an array
* of stacks to avoid ordering the queue (e.g., by using a heap sort.)
* This is a neat problem, because you don't even have to build a
* maze -- you can can use it on any grayscale image!
*
* Rather than using an array of stacks, a more practical
* approach is to implement with a priority queue, which is
* a queue that is sorted so that the elements with the largest
* (or smallest) key values always come off first. The
* priority queue is efficiently implemented as a heap, and
* this is how we do it. Suppose you run the algorithm
* using a priority queue, doing the bookkeeping with an
* auxiliary image data structure that saves the distance of
* each pixel put on the queue as before, according to the method
* described above. We implement it as a 2-way choice by
* initializing the distance array to a large value and putting
* a pixel on the queue if its distance is less than the value
* found on the array. When you finally pop the end pixel from
* the queue, you're done, and you can trace the path backward,
* either always going downhill or using an auxiliary image to
* give you the direction to go at each step. This is implemented
* here in searchGrayMaze().
*
* Do we really have to use a sorted queue? Can we solve this
* generalized maze with an unsorted queue of pixels? (Or even
* an unsorted stack, doing a depth-first search (DFS)?)
* Consider a different algorithm for this generalized maze, where
* we travel again breadth first, but this time use a single,
* unsorted queue. An auxiliary image is used as before to
* store the distances and to determine if pixels get pushed
* on the stack or dropped. As before, we must allow pixels
* to be revisited, with relaxation of the distance if a shorter
* path arrives later. As a result, we will in general have
* multiple instances of the same pixel on the stack with different
* distances. However, because the queue is not ordered, some of
* these pixels will be popped when another instance with a lower
* distance is still on the stack. Here, we're just popping them
* in the order they go on, rather than setting up a priority
* based on minimum distance. Thus, unlike the priority queue,
* when a pixel is popped we have to check the distance map to
* see if a pixel with a lower distance has been put on the queue,
* and, if so, we discard the pixel we just popped. So the
* "while" loop looks like this:
* - pop a pixel from the queue
* - check its distance against the distance stored in the
* distance map; if larger, discard
* - otherwise, for each of its neighbors:
* - compute its distance from the start pixel
* - compare this distance with that on the distance map:
* - if the distance map value higher, relax the distance
* and push the pixel on the queue
* - if the distance map value is lower, discard the pixel
*
* How does this loop terminate? Before, with an ordered queue,
* it terminates when you pop the end pixel. But with an unordered
* queue (or stack), the first time you hit the end pixel, the
* distance is not guaranteed to be correct, because the pixels
* along the shortest path may not have yet been visited and relaxed.
* Because the shortest path can theoretically go anywhere,
* we must keep going. How do we know when to stop? Dijkstra
* uses an ordered queue to systematically remove nodes from
* further consideration. (Each time a pixel is popped, we're
* done with it; it's "finalized" in the Dijkstra sense because
* we know the shortest path to it.) However, with an unordered
* queue, the brute force answer is: stop when the queue
* (or stack) is empty, because then every pixel in the image
* has been assigned its minimum "distance" from the start pixel.
*
* This is similar to the situation when you use a stack for the
* simpler uniform-step problem: with breadth-first search (BFS)
* the pixels on the queue are automatically ordered, so you are
* done when you locate the end pixel as a neighbor of a popped pixel;
* whereas depth-first search (DFS), using a stack, requires,
* in general, a search of every accessible pixel. Further, if
* a pixel is revisited with a smaller distance, that distance is
* recorded and the pixel is put on the stack again.
*
* But surely, you ask, can't we stop sooner? What if the
* start and end pixels are very close to each other?
* OK, suppose they are, and you have very high walls and a
* long snaking level path that is actually the minimum cost.
* That long path can wind back and forth across the entire
* maze many times before ending up at the end point, which
* could be just over a wall from the start. With the unordered
* queue, you very quickly get a high distance for the end
* pixel, which will be relaxed to the minimum distance only
* after all the pixels of the path have been visited and placed
* on the queue, multiple times for many of them. So that's the
* price for not ordering the queue!
*/
PTA *
pixSearchGrayMaze(PIX *pixs,
l_int32 xi,
l_int32 yi,
l_int32 xf,
l_int32 yf,
PIX **ppixd)
{
l_int32 x, y, w, h, d;
l_uint32 val, valr, vals, rpixel, gpixel, bpixel;
void **lines8, **liner32, **linep8;
l_int32 cost, dist, distparent, sival, sivals;
MAZEEL *el, *elp;
PIX *pixd; /* optionally plot the path on this RGB version of pixs */
PIX *pixr; /* for bookkeeping, to indicate the minimum distance */
/* to pixels already visited */
PIX *pixp; /* for bookkeeping, to indicate direction to parent */
L_HEAP *lh;
PTA *pta;
PROCNAME("pixSearchGrayMaze");
if (ppixd) *ppixd = NULL;
if (!pixs)
return (PTA *)ERROR_PTR("pixs not defined", procName, NULL);
pixGetDimensions(pixs, &w, &h, &d);
if (d != 8)
return (PTA *)ERROR_PTR("pixs not 8 bpp", procName, NULL);
if (xi <= 0 || xi >= w)
return (PTA *)ERROR_PTR("xi not valid", procName, NULL);
if (yi <= 0 || yi >= h)
return (PTA *)ERROR_PTR("yi not valid", procName, NULL);
pixd = NULL;
pta = NULL;
pixr = pixCreate(w, h, 32);
pixSetAll(pixr); /* initialize to max value */
pixp = pixCreate(w, h, 8); /* direction to parent stored as enum val */
lines8 = pixGetLinePtrs(pixs, NULL);
linep8 = pixGetLinePtrs(pixp, NULL);
liner32 = pixGetLinePtrs(pixr, NULL);
lh = lheapCreate(0, L_SORT_INCREASING); /* always remove closest pixels */
/* prime the heap with the first pixel */
pixGetPixel(pixs, xi, yi, &val);
el = mazeelCreate(xi, yi, 0); /* don't need direction here */
el->distance = 0;
pixGetPixel(pixs, xi, yi, &val);
el->val = val;
pixSetPixel(pixr, xi, yi, 0); /* distance is 0 */
lheapAdd(lh, el);
/* breadth-first search with priority queue (implemented by
a heap), labeling direction to parents in pixp and minimum
distance to visited pixels in pixr. Stop when we pull
the destination point (xf, yf) off the queue. */
while (lheapGetCount(lh) > 0) {
elp = (MAZEEL *)lheapRemove(lh);
if (!elp)
return (PTA *)ERROR_PTR("heap broken!!", procName, NULL);
x = elp->x;
y = elp->y;
if (x == xf && y == yf) { /* exit condition */
FREE(elp);
break;
}
distparent = (l_int32)elp->distance;
val = elp->val;
sival = val;
if (x > 0) { /* check to west */
vals = GET_DATA_BYTE(lines8[y], x - 1);
valr = GET_DATA_FOUR_BYTES(liner32[y], x - 1);
sivals = (l_int32)vals;
cost = 1 + L_ABS(sivals - sival); /* cost to move to this pixel */
dist = distparent + cost;
if (dist < valr) { /* shortest path so far to this pixel */
SET_DATA_FOUR_BYTES(liner32[y], x - 1, dist); /* new dist */
SET_DATA_BYTE(linep8[y], x - 1, DIR_EAST); /* parent to E */
el = mazeelCreate(x - 1, y, 0);
el->val = vals;
el->distance = dist;
lheapAdd(lh, el);
}
}
if (y > 0) { /* check north */
vals = GET_DATA_BYTE(lines8[y - 1], x);
valr = GET_DATA_FOUR_BYTES(liner32[y - 1], x);
sivals = (l_int32)vals;
cost = 1 + L_ABS(sivals - sival); /* cost to move to this pixel */
dist = distparent + cost;
if (dist < valr) { /* shortest path so far to this pixel */
SET_DATA_FOUR_BYTES(liner32[y - 1], x, dist); /* new dist */
SET_DATA_BYTE(linep8[y - 1], x, DIR_SOUTH); /* parent to S */
el = mazeelCreate(x, y - 1, 0);
el->val = vals;
el->distance = dist;
lheapAdd(lh, el);
}
}
if (x < w - 1) { /* check east */
vals = GET_DATA_BYTE(lines8[y], x + 1);
valr = GET_DATA_FOUR_BYTES(liner32[y], x + 1);
sivals = (l_int32)vals;
cost = 1 + L_ABS(sivals - sival); /* cost to move to this pixel */
dist = distparent + cost;
if (dist < valr) { /* shortest path so far to this pixel */
SET_DATA_FOUR_BYTES(liner32[y], x + 1, dist); /* new dist */
SET_DATA_BYTE(linep8[y], x + 1, DIR_WEST); /* parent to W */
el = mazeelCreate(x + 1, y, 0);
el->val = vals;
el->distance = dist;
lheapAdd(lh, el);
}
}
if (y < h - 1) { /* check south */
vals = GET_DATA_BYTE(lines8[y + 1], x);
valr = GET_DATA_FOUR_BYTES(liner32[y + 1], x);
sivals = (l_int32)vals;
cost = 1 + L_ABS(sivals - sival); /* cost to move to this pixel */
dist = distparent + cost;
if (dist < valr) { /* shortest path so far to this pixel */
SET_DATA_FOUR_BYTES(liner32[y + 1], x, dist); /* new dist */
SET_DATA_BYTE(linep8[y + 1], x, DIR_NORTH); /* parent to N */
el = mazeelCreate(x, y + 1, 0);
el->val = vals;
el->distance = dist;
lheapAdd(lh, el);
}
}
FREE(elp);
}
lheapDestroy(&lh, TRUE);
if (ppixd) {
pixd = pixConvert8To32(pixs);
*ppixd = pixd;
}
composeRGBPixel(255, 0, 0, &rpixel); /* start point */
composeRGBPixel(0, 255, 0, &gpixel);
composeRGBPixel(0, 0, 255, &bpixel); /* end point */
x = xf;
y = yf;
pta = ptaCreate(0);
while (1) { /* write path onto pixd */
ptaAddPt(pta, x, y);
if (x == xi && y == yi)
break;
if (pixd)
pixSetPixel(pixd, x, y, gpixel);
pixGetPixel(pixp, x, y, &val);
if (val == DIR_NORTH)
y--;
else if (val == DIR_SOUTH)
y++;
else if (val == DIR_EAST)
x++;
else if (val == DIR_WEST)
x--;
pixGetPixel(pixr, x, y, &val);
#if DEBUG_PATH
fprintf(stderr, "(x,y) = (%d, %d); dist = %d\n", x, y, val);
#endif /* DEBUG_PATH */
}
if (pixd) {
pixSetPixel(pixd, xi, yi, rpixel);
pixSetPixel(pixd, xf, yf, bpixel);
}
pixDestroy(&pixp);
pixDestroy(&pixr);
FREE(lines8);
FREE(linep8);
FREE(liner32);
return pta;
}
/*---------------------------------------------------------------------*
* Display Path(s) *
*---------------------------------------------------------------------*/
/*!
* pixDisplayPta()
*
* Input: pixs (1, 2, 4, 8, 16 or 32 bpp)
* pta (of path to be plotted)
* Return: pixd (32 bpp RGB version of pixs, with path in green),
* or null on error
*/
PIX *
pixDisplayPta(PIX *pixs,
PTA *pta)
{
l_int32 i, n, x, y;
l_uint32 rpixel, gpixel, bpixel;
PIX *pixd;
PROCNAME("pixDisplayPta");
if (!pixs)
return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
if (!pta)
return (PIX *)ERROR_PTR("pta not defined", procName, NULL);
if ((pixd = pixConvertTo32(pixs)) == NULL)
return (PIX *)ERROR_PTR("pixd not made", procName, NULL);
composeRGBPixel(255, 0, 0, &rpixel); /* start point */
composeRGBPixel(0, 255, 0, &gpixel);
composeRGBPixel(0, 0, 255, &bpixel); /* end point */
n = ptaGetCount(pta);
for (i = 0; i < n; i++) {
ptaGetIPt(pta, i, &x, &y);
if (i == 0)
pixSetPixel(pixd, x, y, rpixel);
else if (i < n - 1)
pixSetPixel(pixd, x, y, gpixel);
else
pixSetPixel(pixd, x, y, bpixel);
}
return pixd;
}
/*!
* pixDisplayPtaa()
*
* Input: pixs (1, 2, 4, 8, 16 or 32 bpp)
* ptaa (array of paths to be plotted)
* Return: pixd (32 bpp RGB version of pixs, with paths plotted
* in different colors), or null on error
*/
PIX *
pixDisplayPtaa(PIX *pixs,
PTAA *ptaa)
{
l_int32 i, j, npta, npt, x, y;
l_int32 rv, gv, bv;
l_uint32 *pixela;
PIX *pixd;
PTA *pta;
PROCNAME("pixDisplayPtaa");
if (!pixs)
return (PIX *)ERROR_PTR("pixs not defined", procName, NULL);
if (!ptaa)
return (PIX *)ERROR_PTR("ptaa not defined", procName, NULL);
npta = ptaaGetCount(ptaa);
if (npta == 0)
return (PIX *)ERROR_PTR("no pta", procName, NULL);
if ((pixd = pixConvertTo32(pixs)) == NULL)
return (PIX *)ERROR_PTR("pixd not made", procName, NULL);
/* make a colormap for the paths; this one approximates
* three functions that are linear for each color over
* half the number of paths. */
pixela = (l_uint32 *)CALLOC(npta, sizeof(l_uint32));
for (i = 0; i < npta; i++) {
rv = L_MAX(0, 255 - 255 * (2 * i) / (npta + 1));
bv = L_MIN(255, L_MAX(0, (255 * (3 + 2 * i - npta) / (npta + 1))));
if (i < npta / 2)
gv = L_MIN(255, (255 * 2 * i) / (npta + 1));
else
gv = L_MIN(255, L_MAX(0, 255 - 255 * (2 * i - npta) / npta));
/* fprintf(stderr, "rv = %d, gv = %d, bv = %d\n", rv, gv, bv); */
composeRGBPixel(rv, gv, bv, &pixela[i]);
}
for (i = 0; i < npta; i++) {
pta = ptaaGetPta(ptaa, i, L_CLONE);
npt = ptaGetCount(pta);
for (j = 0; j < npt; j++) {
ptaGetIPt(pta, j, &x, &y);
pixSetPixel(pixd, x, y, pixela[i]);
}
ptaDestroy(&pta);
}
FREE(pixela);
return pixd;
}
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