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Prescan for small deltas before doing proper simplification
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@e-n-f
e-n-f committed Aug 6, 2024
1 parent b329489 commit d1d8238
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Showing 2 changed files with 64 additions and 12 deletions.
24 changes: 15 additions & 9 deletions clip.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -789,14 +789,14 @@ double distance_from_line(long long point_x, long long point_y, long long segA_x
void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, size_t retain, bool prevent_simplify_shared_nodes) {
std::stack<int> recursion_stack;

if (!geom[start + 0].necessary || !geom[start + n - 1].necessary) {
if (!(geom[start + 0].necessary > 0) || !(geom[start + n - 1].necessary > 0)) {
fprintf(stderr, "endpoints not marked necessary\n");
exit(EXIT_IMPOSSIBLE);
}

int prev = 0;
for (int here = 1; here < n; here++) {
if (geom[start + here].necessary) {
if (geom[start + here].necessary > 0) {
recursion_stack.push(prev);
recursion_stack.push(here);
prev = here;
Expand Down Expand Up @@ -829,9 +829,12 @@ void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, siz
if (geom[start + first] < geom[start + second]) {
farthest_element_index = first;
for (i = first + 1; i < second; i++) {
double temp_dist = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + first].x, geom[start + first].y, geom[start + second].x, geom[start + second].y);

double distance = std::fabs(temp_dist);
double distance;
if (geom[start + i].necessary < 0) {
distance = 0;
} else {
distance = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + first].x, geom[start + first].y, geom[start + second].x, geom[start + second].y);
}

if ((distance > e || kept < retain) && (distance > max_distance || (distance == max_distance && geom[start + i] < geom[start + farthest_element_index]))) {
farthest_element_index = i;
Expand All @@ -841,9 +844,12 @@ void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, siz
} else {
farthest_element_index = second;
for (i = second - 1; i > first; i--) {
double temp_dist = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + second].x, geom[start + second].y, geom[start + first].x, geom[start + first].y);

double distance = std::fabs(temp_dist);
double distance;
if (geom[start + i].necessary < 0) {
distance = 0;
} else {
distance = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + second].x, geom[start + second].y, geom[start + first].x, geom[start + first].y);
}

if ((distance > e || kept < retain) && (distance > max_distance || (distance == max_distance && geom[start + i] < geom[start + farthest_element_index]))) {
farthest_element_index = i;
Expand Down Expand Up @@ -917,7 +923,7 @@ static drawvec simplify_lines_basic(drawvec &geom, int z, int detail, double sim

size_t out = 0;
for (size_t i = 0; i < geom.size(); i++) {
if (geom[i].necessary) {
if (geom[i].necessary > 0) {
geom[out++] = geom[i];
}
}
Expand Down
52 changes: 49 additions & 3 deletions geometry.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,48 @@ drawvec impose_tile_boundaries(const drawvec &geom, long long extent) {
return out;
}

static void mark_unnecessary(drawvec &geom, size_t start, size_t end, double e) {
double ee = e * e;

if (geom[start] < geom[end]) {
size_t last = start;
for (size_t i = start + 1; i < end; i++) {
long long dx = geom[i].x - geom[last].x;
long long dy = geom[i].y - geom[last].y;
if (dx * dx + dy * dy < ee) {
geom[i].necessary = -1;
} else {
last = i;
}
}
} else {
size_t last = end;
for (size_t i = end - 1; i > start; i--) {
long long dx = geom[i].x - geom[last].x;
long long dy = geom[i].y - geom[last].y;
if (dx * dx + dy * dy < ee) {
geom[i].necessary = -1;
} else {
last = i;
}
}
}
}

static void mark_unnecessary(drawvec &geom, double e) {
for (size_t i = 0; i < geom.size(); i++) {
if (geom[i].necessary > 0) {
for (size_t j = i + 1; j < geom.size(); j++) {
if (geom[j].necessary > 0) {
mark_unnecessary(geom, i, j, e);
i = j - 1;
break;
}
}
}
}
}

drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool mark_tile_bounds, double simplification, size_t retain, drawvec const &shared_nodes, struct node *shared_nodes_map, size_t nodepos, std::string const &shared_nodes_bloom) {
int res = 1 << (32 - detail - z);
long long area = 1LL << (32 - z);
Expand All @@ -265,7 +307,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma

auto pt = std::lower_bound(shared_nodes.begin(), shared_nodes.end(), geom[i]);
if (pt != shared_nodes.end() && *pt == geom[i]) {
geom[i].necessary = true;
geom[i].necessary = 1;
}

if (nodepos > 0) {
Expand All @@ -284,7 +326,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma

if (shared_nodes_bloom[bloom_ix] & bloom_mask) {
if (bsearch(&n, shared_nodes_map, nodepos / sizeof(node), sizeof(node), nodecmp) != NULL) {
geom[i].necessary = true;
geom[i].necessary = 1;
}
}
}
Expand All @@ -295,6 +337,10 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
geom = impose_tile_boundaries(geom, area);
}

if (!additional[A_VISVALINGAM]) {
mark_unnecessary(geom, res * simplification);
}

for (size_t i = 0; i < geom.size(); i++) {
if (geom[i].op == VT_MOVETO) {
size_t j;
Expand Down Expand Up @@ -327,7 +373,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma

size_t out = 0;
for (size_t i = 0; i < geom.size(); i++) {
if (geom[i].necessary) {
if (geom[i].necessary > 0) {
geom[out++] = geom[i];
}
}
Expand Down

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