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BLI_bitmap_draw_2d: optimize polygon filling

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Existing method was fine for basic polygons but didn't scale well
because its was checking all coordinates for every y-pixel.

Heres an optimized version.
Basic logic remains the same this just maintains an ordered list of intersections,
tracking in-out points, to avoid re-computing every row,
this means sorting is only done once when out of order segments are found,
the segments only need to be re-ordered if they cross each other.

Speedup isn't linear, test with full-screen complex lasso gave 11x speedup.
This commit is contained in:
Campbell Barton 2016-10-26 20:26:32 +11:00
parent 8125271ddb
commit 44522a5b98
1 changed files with 185 additions and 35 deletions
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220
source/blender/blenlib/intern/bitmap_draw_2d.c
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@ -29,14 +29,21 @@
* Utility functions for primitive drawing operations.
*/
#include <limits.h>
#include "MEM_guardedalloc.h"
#include "BLI_bitmap_draw_2d.h"
#include "BLI_math_base.h"
#include "BLI_sort.h"
#include "BLI_utildefines.h"
#include "BLI_strict_flags.h"
/* -------------------------------------------------------------------- */
/* Draw Line */
/**
* Plot a line from \a p1 to \a p2 (inclusive).
*/
@ -107,7 +114,51 @@ void BLI_bitmap_draw_2d_line_v2v2i(
}
}
/* -------------------------------------------------------------------- */
/* Draw Filled Polygon */
/* sort edge-segments on y, then x axis */
static int draw_poly_v2i_n__span_y_sort(const void *a_p, const void *b_p, void *verts_p)
{
const int (*verts)[2] = verts_p;
const int *a = a_p;
const int *b = b_p;
const int *co_a = verts[a[0]];
const int *co_b = verts[b[0]];
if (co_a[1] < co_b[1]) {
return -1;
}
else if (co_a[1] > co_b[1]) {
return 1;
}
else if (co_a[0] < co_b[0]) {
return -1;
}
else if (co_a[0] > co_b[0]) {
return 1;
}
else {
/* co_a & co_b are identical, use the line closest to the x-min */
const int *co = co_a;
co_a = verts[a[1]];
co_b = verts[b[1]];
int ord = (((co_b[0] - co[0]) * (co_a[1] - co[1])) -
((co_a[0] - co[0]) * (co_b[1] - co[1])));
if (ord > 0) {
return -1;
}
if (ord < 0) {
return 1;
}
}
return 0;
}
/**
* Draws a filled polyon with support for self intersections.
*
* \param callback: Takes the x, y coords and x-span (\a x_end is not inclusive),
* note that \a x_end will always be greater than \a x, so we can use:
*
@ -123,59 +174,158 @@ void BLI_bitmap_draw_2d_poly_v2i_n(
void (*callback)(int x, int x_end, int y, void *), void *userData)
{
/* Originally by Darel Rex Finley, 2007.
*/
* Optimized by Campbell Barton, 2016 to track sorted intersections. */
int nodes, pixel_y, i, j, swap;
int *node_x = MEM_mallocN(sizeof(*node_x) * (size_t)(nr + 1), __func__);
int (*span_y)[2] = MEM_mallocN(sizeof(*span_y) * (size_t)nr, __func__);
int span_y_len = 0;
for (int i_curr = 0, i_prev = nr - 1; i_curr < nr; i_prev = i_curr++) {
const int *co_prev = verts[i_prev];
const int *co_curr = verts[i_curr];
if (co_prev[1] != co_curr[1]) {
/* Any segments entirely above or below the area of interest can be skipped. */
if ((min_ii(co_prev[1], co_curr[1]) >= ymax) ||
(max_ii(co_prev[1], co_curr[1]) < ymin))
{
continue;
}
int *s = span_y[span_y_len++];
if (co_prev[1] < co_curr[1]) {
s[0] = i_prev;
s[1] = i_curr;
}
else {
s[0] = i_curr;
s[1] = i_prev;
}
}
}
BLI_qsort_r(span_y, (size_t)span_y_len, sizeof(*span_y), draw_poly_v2i_n__span_y_sort, (void *)verts);
struct NodeX {
int span_y_index;
int x;
} *node_x = MEM_mallocN(sizeof(*node_x) * (size_t)(nr + 1), __func__);
int node_x_len = 0;
int span_y_index = 0;
if (span_y_len != 0 && verts[span_y[0][0]][1] < ymin) {
while ((span_y_index < span_y_len) &&
(verts[span_y[span_y_index][0]][1] < ymin))
{
BLI_assert(verts[span_y[span_y_index][0]][1] <
verts[span_y[span_y_index][1]][1]);
if (verts[span_y[span_y_index][1]][1] >= ymin) {
struct NodeX *n = &node_x[node_x_len++];
n->span_y_index = span_y_index;
}
span_y_index += 1;
}
}
/* Loop through the rows of the image. */
for (pixel_y = ymin; pixel_y < ymax; pixel_y++) {
for (int pixel_y = ymin; pixel_y < ymax; pixel_y++) {
bool is_sorted = true;
bool do_remove = false;
/* Build a list of nodes. */
nodes = 0; j = nr - 1;
for (i = 0; i < nr; i++) {
if ((verts[i][1] < pixel_y && verts[j][1] >= pixel_y) ||
(verts[j][1] < pixel_y && verts[i][1] >= pixel_y))
{
node_x[nodes++] = (int)(verts[i][0] +
((double)(pixel_y - verts[i][1]) / (verts[j][1] - verts[i][1])) *
(verts[j][0] - verts[i][0]));
for (int i = 0, x_ix_prev = INT_MIN; i < node_x_len; i++) {
struct NodeX *n = &node_x[i];
const int *s = span_y[n->span_y_index];
const int *co_prev = verts[s[0]];
const int *co_curr = verts[s[1]];
BLI_assert(co_prev[1] < pixel_y && co_curr[1] >= pixel_y);
const double x = (co_prev[0] - co_curr[0]);
const double y = (co_prev[1] - co_curr[1]);
const double y_px = (pixel_y - co_curr[1]);
const int x_ix = (int)((double)co_curr[0] + ((y_px / y) * x));
n->x = x_ix;
if (is_sorted && (x_ix_prev > x_ix)) {
is_sorted = false;
}
j = i;
if (do_remove == false && co_curr[1] == pixel_y) {
do_remove = true;
}
x_ix_prev = x_ix;
}
/* Sort the nodes, via a simple "Bubble" sort. */
i = 0;
while (i < nodes - 1) {
if (node_x[i] > node_x[i + 1]) {
SWAP_TVAL(swap, node_x[i], node_x[i + 1]);
if (i) i--;
}
else {
i++;
if (is_sorted == false) {
int i = 0;
const int node_x_end = node_x_len - 1;
while (i < node_x_end) {
if (node_x[i].x > node_x[i + 1].x) {
SWAP(struct NodeX, node_x[i], node_x[i + 1]);
if (i != 0) {
i -= 1;
}
}
else {
i += 1;
}
}
}
/* Fill the pixels between node pairs. */
for (i = 0; i < nodes; i += 2) {
if (node_x[i] >= xmax) break;
if (node_x[i + 1] > xmin) {
if (node_x[i ] < xmin) node_x[i ] = xmin;
if (node_x[i + 1] > xmax) node_x[i + 1] = xmax;
for (int i = 0; i < node_x_len; i += 2) {
int x_src = node_x[i].x;
int x_dst = node_x[i + 1].x;
#if 0
/* for many x/y calls */
for (j = node_x[i]; j < node_x[i + 1]; j++) {
callback(j - xmin, pixel_y - ymin, userData);
if (x_src >= xmax) {
break;
}
if (x_dst > xmin) {
if (x_src < xmin) {
x_src = xmin;
}
if (x_dst > xmax) {
x_dst = xmax;
}
#else
/* for single call per x-span */
if (node_x[i] < node_x[i + 1]) {
callback(node_x[i] - xmin, node_x[i + 1] - xmin, pixel_y - ymin, userData);
if (x_src < x_dst) {
callback(x_src - xmin, x_dst - xmin, pixel_y - ymin, userData);
}
#endif
}
}
/* Clear finalized nodes in one pass, only when needed
* (avoids excessive array-resizing). */
if (do_remove == true) {
int i_dst = 0;
for (int i_src = 0; i_src < node_x_len; i_src += 1) {
const int *s = span_y[node_x[i_src].span_y_index];
const int *co = verts[s[1]];
if (co[1] != pixel_y) {
if (i_dst != i_src) {
/* x is initialized for the next pixel_y (no need to adjust here) */
node_x[i_dst].span_y_index = node_x[i_src].span_y_index;
}
i_dst += 1;
}
}
node_x_len = i_dst;
}
/* Scan for new x-nodes */
while ((span_y_index < span_y_len) &&
(verts[span_y[span_y_index][0]][1] == pixel_y))
{
/* note, node_x these are just added at the end,
* not ideal but sorting once will resolve. */
/* x is initialized for the next pixel_y */
struct NodeX *n = &node_x[node_x_len++];
n->span_y_index = span_y_index;
span_y_index += 1;
}
}
MEM_freeN(span_y);
MEM_freeN(node_x);
}