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imgui/stb_rect_pack.h

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// stb_rect_pack.h - v0.05 - public domain - rectangle packing
// Sean Barrett 2014
//
// Useful for e.g. packing rectangular textures into an atlas.
// Does not do rotation.
//
// Not necessarily the awesomest packing method, but better than
// the totally naive one in stb_truetype (which is primarily what
// this is meant to replace).
//
// Has only had a few tests run, may have issues.
//
// More docs to come.
//
// No memory allocations; uses qsort() and assert() from stdlib.
//
// This library currently uses the Skyline Bottom-Left algorithm.
//
// Please note: better rectangle packers are welcome! Please
// implement them to the same API, but with a different init
// function.
//
// Version history:
//
// 0.05: added STBRP_ASSERT to allow replacing assert
// 0.04: fixed minor bug in STBRP_LARGE_RECTS support
// 0.01: initial release
//////////////////////////////////////////////////////////////////////////////
//
// INCLUDE SECTION
//
#ifndef STB_INCLUDE_STB_RECT_PACK_H
#define STB_INCLUDE_STB_RECT_PACK_H
#define STB_RECT_PACK_VERSION 1
#ifdef STBRP_STATIC
#define STBRP_DEF static
#else
#define STBRP_DEF extern
#endif
#ifdef __cplusplus
extern "C" {
#endif
typedef struct stbrp_context stbrp_context;
typedef struct stbrp_node stbrp_node;
typedef struct stbrp_rect stbrp_rect;
#ifdef STBRP_LARGE_RECTS
typedef int stbrp_coord;
#else
typedef unsigned short stbrp_coord;
#endif
STBRP_DEF void stbrp_pack_rects (stbrp_context *context, stbrp_rect *rects, int num_rects);
// Assign packed locations to rectangles. The rectangles are of type
// 'stbrp_rect' defined below, stored in the array 'rects', and there
// are 'num_rects' many of them.
//
// Rectangles which are successfully packed have the 'was_packed' flag
// set to a non-zero value and 'x' and 'y' store the minimum location
// on each axis (i.e. bottom-left in cartesian coordinates, top-left
// if you imagine y increasing downwards). Rectangles which do not fit
// have the 'was_packed' flag set to 0.
//
// You should not try to access the 'rects' array from another thread
// while this function is running, as the function temporarily reorders
// the array while it executes.
//
// To pack into another rectangle, you need to call stbrp_init_target
// again. To continue packing into the same rectangle, you can call
// this function again. Calling this multiple times with multiple rect
// arrays will probably produce worse packing results than calling it
// a single time with the full rectangle array, but the option is
// available.
struct stbrp_rect
{
// reserved for your use:
int id;
// input:
stbrp_coord w, h;
// output:
stbrp_coord x, y;
int was_packed; // non-zero if valid packing
}; // 16 bytes, nominally
STBRP_DEF void stbrp_init_target (stbrp_context *context, int width, int height, stbrp_node *nodes, int num_nodes);
// Initialize a rectangle packer to:
// pack a rectangle that is 'width' by 'height' in dimensions
// using temporary storage provided by the array 'nodes', which is 'num_nodes' long
//
// You must call this function every time you start packing into a new target.
//
// There is no "shutdown" function. The 'nodes' memory must stay valid for
// the following stbrp_pack_rects() call (or calls), but can be freed after
// the call (or calls) finish.
//
// Note: to guarantee best results, either:
// 1. make sure 'num_nodes' >= 'width'
// or 2. call stbrp_allow_out_of_mem() defined below with 'allow_out_of_mem = 1'
//
// If you don't do either of the above things, widths will be quantized to multiples
// of small integers to guarantee the algorithm doesn't run out of temporary storage.
//
// If you do #2, then the non-quantized algorithm will be used, but the algorithm
// may run out of temporary storage and be unable to pack some rectangles.
STBRP_DEF void stbrp_setup_allow_out_of_mem (stbrp_context *context, int allow_out_of_mem);
// Optionally call this function after init but before doing any packing to
// change the handling of the out-of-temp-memory scenario, described above.
// If you call init again, this will be reset to the default (false).
STBRP_DEF void stbrp_setup_heuristic (stbrp_context *context, int heuristic);
// Optionally select which packing heuristic the library should use. Different
// heuristics will produce better/worse results for different data sets.
// If you call init again, this will be reset to the default.
enum
{
STBRP_HEURISTIC_Skyline_default=0,
STBRP_HEURISTIC_Skyline_BL_sortHeight = STBRP_HEURISTIC_Skyline_default,
STBRP_HEURISTIC_Skyline_BF_sortHeight
};
//////////////////////////////////////////////////////////////////////////////
//
// the details of the following structures don't matter to you, but they must
// be visible so you can handle the memory allocations for them
struct stbrp_node
{
stbrp_coord x,y;
stbrp_node *next;
};
struct stbrp_context
{
int width;
int height;
int align;
int init_mode;
int heuristic;
int num_nodes;
stbrp_node *active_head;
stbrp_node *free_head;
stbrp_node extra[2]; // we allocate two extra nodes so optimal user-node-count is 'width' not 'width+2'
};
#ifdef __cplusplus
}
#endif
#endif
//////////////////////////////////////////////////////////////////////////////
//
// IMPLEMENTATION SECTION
//
#ifdef STB_RECT_PACK_IMPLEMENTATION
#include <stdlib.h>
#ifndef STBRP_ASSERT
#include <assert.h>
#define STBRP_ASSERT assert
#endif
enum
{
STBRP__INIT_skyline = 1
};
STBRP_DEF void stbrp_setup_heuristic(stbrp_context *context, int heuristic)
{
switch (context->init_mode) {
case STBRP__INIT_skyline:
STBRP_ASSERT(heuristic == STBRP_HEURISTIC_Skyline_BL_sortHeight || heuristic == STBRP_HEURISTIC_Skyline_BF_sortHeight);
context->heuristic = heuristic;
break;
default:
STBRP_ASSERT(0);
}
}
STBRP_DEF void stbrp_setup_allow_out_of_mem(stbrp_context *context, int allow_out_of_mem)
{
if (allow_out_of_mem)
// if it's ok to run out of memory, then don't bother aligning them;
// this gives better packing, but may fail due to OOM (even though
// the rectangles easily fit). @TODO a smarter approach would be to only
// quantize once we've hit OOM, then we could get rid of this parameter.
context->align = 1;
else {
// if it's not ok to run out of memory, then quantize the widths
// so that num_nodes is always enough nodes.
//
// I.e. num_nodes * align >= width
// align >= width / num_nodes
// align = ceil(width/num_nodes)
context->align = (context->width + context->num_nodes-1) / context->num_nodes;
}
}
STBRP_DEF void stbrp_init_target(stbrp_context *context, int width, int height, stbrp_node *nodes, int num_nodes)
{
int i;
#ifndef STBRP_LARGE_RECTS
STBRP_ASSERT(width <= 0xffff && height <= 0xffff);
#endif
for (i=0; i < num_nodes-1; ++i)
nodes[i].next = &nodes[i+1];
nodes[i].next = NULL;
context->init_mode = STBRP__INIT_skyline;
context->heuristic = STBRP_HEURISTIC_Skyline_default;
context->free_head = &nodes[0];
context->active_head = &context->extra[0];
context->width = width;
context->height = height;
context->num_nodes = num_nodes;
stbrp_setup_allow_out_of_mem(context, 0);
// node 0 is the full width, node 1 is the sentinel (lets us not store width explicitly)
context->extra[0].x = 0;
context->extra[0].y = 0;
context->extra[0].next = &context->extra[1];
context->extra[1].x = (stbrp_coord) width;
#ifdef STBRP_LARGE_RECTS
context->extra[1].y = (1<<30);
#else
context->extra[1].y = 65535;
#endif
context->extra[1].next = NULL;
}
// find minimum y position if it starts at x1
static int stbrp__skyline_find_min_y(stbrp_context *c, stbrp_node *first, int x0, int width, int *pwaste)
{
(void)c;
stbrp_node *node = first;
int x1 = x0 + width;
int min_y, visited_width, waste_area;
STBRP_ASSERT(first->x <= x0);
#if 0
// skip in case we're past the node
while (node->next->x <= x0)
++node;
#else
STBRP_ASSERT(node->next->x > x0); // we ended up handling this in the caller for efficiency
#endif
STBRP_ASSERT(node->x <= x0);
min_y = 0;
waste_area = 0;
visited_width = 0;
while (node->x < x1) {
if (node->y > min_y) {
// raise min_y higher.
// we've accounted for all waste up to min_y,
// but we'll now add more waste for everything we've visted
waste_area += visited_width * (node->y - min_y);
min_y = node->y;
// the first time through, visited_width might be reduced
if (node->x < x0)
visited_width += node->next->x - x0;
else
visited_width += node->next->x - node->x;
} else {
// add waste area
int under_width = node->next->x - node->x;
if (under_width + visited_width > width)
under_width = width - visited_width;
waste_area += under_width * (min_y - node->y);
visited_width += under_width;
}
node = node->next;
}
*pwaste = waste_area;
return min_y;
}
typedef struct
{
int x,y;
stbrp_node **prev_link;
} stbrp__findresult;
static stbrp__findresult stbrp__skyline_find_best_pos(stbrp_context *c, int width, int height)
{
int best_waste = (1<<30), best_x, best_y = (1 << 30);
stbrp__findresult fr;
stbrp_node **prev, *node, *tail, **best = NULL;
// align to multiple of c->align
width = (width + c->align - 1);
width -= width % c->align;
STBRP_ASSERT(width % c->align == 0);
node = c->active_head;
prev = &c->active_head;
while (node->x + width <= c->width) {
int y,waste;
y = stbrp__skyline_find_min_y(c, node, node->x, width, &waste);
if (c->heuristic == STBRP_HEURISTIC_Skyline_BL_sortHeight) { // actually just want to test BL
// bottom left
if (y < best_y) {
best_y = y;
best = prev;
}
} else {
// best-fit
if (y + height <= c->height) {
// can only use it if it first vertically
if (y < best_y || (y == best_y && waste < best_waste)) {
best_y = y;
best_waste = waste;
best = prev;
}
}
}
prev = &node->next;
node = node->next;
}
best_x = (best == NULL) ? 0 : (*best)->x;
// if doing best-fit (BF), we also have to try aligning right edge to each node position
//
// e.g, if fitting
//
// ____________________
// |____________________|
//
// into
//
// | |
// | ____________|
// |____________|
//
// then right-aligned reduces waste, but bottom-left BL is always chooses left-aligned
//
// This makes BF take about 2x the time
if (c->heuristic == STBRP_HEURISTIC_Skyline_BF_sortHeight) {
tail = c->active_head;
node = c->active_head;
prev = &c->active_head;
// find first node that's admissible
while (tail->x < width)
tail = tail->next;
while (tail) {
int xpos = tail->x - width;
int y,waste;
STBRP_ASSERT(xpos >= 0);
// find the left position that matches this
while (node->next->x <= xpos) {
prev = &node->next;
node = node->next;
}
STBRP_ASSERT(node->next->x > xpos && node->x <= xpos);
y = stbrp__skyline_find_min_y(c, node, xpos, width, &waste);
if (y + height < c->height) {
if (y <= best_y) {
if (y < best_y || waste < best_waste || (waste==best_waste && xpos < best_x)) {
best_x = xpos;
STBRP_ASSERT(y <= best_y);
best_y = y;
best_waste = waste;
best = prev;
}
}
}
tail = tail->next;
}
}
fr.prev_link = best;
fr.x = best_x;
fr.y = best_y;
return fr;
}
static stbrp__findresult stbrp__skyline_pack_rectangle(stbrp_context *context, int width, int height)
{
// find best position according to heuristic
stbrp__findresult res = stbrp__skyline_find_best_pos(context, width, height);
stbrp_node *node, *cur;
// bail if:
// 1. it failed
// 2. the best node doesn't fit (we don't always check this)
// 3. we're out of memory
if (res.prev_link == NULL || res.y + height > context->height || context->free_head == NULL) {
res.prev_link = NULL;
return res;
}
// on success, create new node
node = context->free_head;
node->x = (stbrp_coord) res.x;
node->y = (stbrp_coord) (res.y + height);
context->free_head = node->next;
// insert the new node into the right starting point, and
// let 'cur' point to the remaining nodes needing to be
// stiched back in
cur = *res.prev_link;
if (cur->x < res.x) {
// preserve the existing one, so start testing with the next one
stbrp_node *next = cur->next;
cur->next = node;
cur = next;
} else {
*res.prev_link = node;
}
// from here, traverse cur and free the nodes, until we get to one
// that shouldn't be freed
while (cur->next && cur->next->x <= res.x + width) {
stbrp_node *next = cur->next;
// move the current node to the free list
cur->next = context->free_head;
context->free_head = cur;
cur = next;
}
// stitch the list back in
node->next = cur;
if (cur->x < res.x + width)
cur->x = (stbrp_coord) (res.x + width);
#ifdef _DEBUG
cur = context->active_head;
while (cur->x < context->width) {
STBRP_ASSERT(cur->x < cur->next->x);
cur = cur->next;
}
STBRP_ASSERT(cur->next == NULL);
{
stbrp_node *L1 = NULL, *L2 = NULL;
int count=0;
cur = context->active_head;
while (cur) {
L1 = cur;
cur = cur->next;
++count;
}
cur = context->free_head;
while (cur) {
L2 = cur;
cur = cur->next;
++count;
}
STBRP_ASSERT(count == context->num_nodes+2);
}
#endif
return res;
}
static int rect_height_compare(const void *a, const void *b)
{
stbrp_rect *p = (stbrp_rect *) a;
stbrp_rect *q = (stbrp_rect *) b;
if (p->h > q->h)
return -1;
if (p->h < q->h)
return 1;
return (p->w > q->w) ? -1 : (p->w < q->w);
}
static int rect_width_compare(const void *a, const void *b)
{
stbrp_rect *p = (stbrp_rect *) a;
stbrp_rect *q = (stbrp_rect *) b;
if (p->w > q->w)
return -1;
if (p->w < q->w)
return 1;
return (p->h > q->h) ? -1 : (p->h < q->h);
}
static int rect_original_order(const void *a, const void *b)
{
stbrp_rect *p = (stbrp_rect *) a;
stbrp_rect *q = (stbrp_rect *) b;
return (p->was_packed < q->was_packed) ? -1 : (p->was_packed > q->was_packed);
}
#ifdef STBRP_LARGE_RECTS
#define STBRP__MAXVAL 0xffffffff
#else
#define STBRP__MAXVAL 0xffff
#endif
STBRP_DEF void stbrp_pack_rects(stbrp_context *context, stbrp_rect *rects, int num_rects)
{
int i;
// we use the 'was_packed' field internally to allow sorting/unsorting
for (i=0; i < num_rects; ++i) {
rects[i].was_packed = i;
#ifndef STBRP_LARGE_RECTS
STBRP_ASSERT(rects[i].w <= 0xffff && rects[i].h <= 0xffff);
#endif
}
// sort according to heuristic
qsort(rects, num_rects, sizeof(rects[0]), rect_height_compare);
for (i=0; i < num_rects; ++i) {
stbrp__findresult fr = stbrp__skyline_pack_rectangle(context, rects[i].w, rects[i].h);
if (fr.prev_link) {
rects[i].x = (stbrp_coord) fr.x;
rects[i].y = (stbrp_coord) fr.y;
} else {
rects[i].x = rects[i].y = STBRP__MAXVAL;
}
}
// unsort
qsort(rects, num_rects, sizeof(rects[0]), rect_original_order);
// set was_packed flags
for (i=0; i < num_rects; ++i)
rects[i].was_packed = !(rects[i].x == STBRP__MAXVAL && rects[i].y == STBRP__MAXVAL);
}
#endif
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