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[core] change approach to stencil clipping to (almost) match JS

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This commit is contained in:
Konstantin Käfer
2019-04-16 17:44:34 +02:00
parent 8f5e1ba20f
commit 08163713e2
27 changed files with 139 additions and 958 deletions
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39
src/mbgl/algorithm/covered_by_children.hpp
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#pragma once
#include <mbgl/tile/tile_id.hpp>
namespace mbgl {
namespace algorithm {
template <typename Iterator>
bool coveredByChildren(const UnwrappedTileID& id, Iterator it, const Iterator& end) {
for (const auto& child : id.children()) {
it = std::lower_bound(it, end, child, [](const auto& a, const auto& b) { return std::get<0>(a) < b; });
// Child is not present, neither its grandchildren.
if (it == end) {
return false;
}
// Child is not present, but its grandchildren are.
if (std::get<0>(*it) != child) {
// This child is not covered by its grandchildren.
if (!coveredByChildren(child, it, end)) {
return false;
}
}
}
// We looked at all four children (recursively) and verified that they're covered.
return true;
}
template <typename Container>
bool coveredByChildren(const UnwrappedTileID& id, const Container& container) {
return coveredByChildren(
id, container.upper_bound(id),
container.lower_bound(UnwrappedTileID{ static_cast<int16_t>(id.wrap + 1), { 0, 0, 0 } }));
}
} // namespace algorithm
} // namespace mbgl

76
src/mbgl/algorithm/generate_clip_ids.cpp
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#include <mbgl/algorithm/generate_clip_ids_impl.hpp>
#include <mbgl/algorithm/covered_by_children.hpp>
#include <mbgl/util/std.hpp>
#include <list>
#include <vector>
#include <bitset>
#include <cassert>
#include <algorithm>
#include <iterator>
namespace mbgl {
namespace algorithm {
ClipIDGenerator::Leaf::Leaf(ClipID& clip_) : clip(clip_) {
}
void ClipIDGenerator::Leaf::add(const CanonicalTileID& p) {
// Ensure that no already present child is a parent of the new p.
for (const auto& child : children) {
if (p.isChildOf(child)) {
return;
}
}
children.emplace(p);
}
bool ClipIDGenerator::Leaf::operator==(const Leaf& other) const {
return children == other.children;
}
std::map<UnwrappedTileID, ClipID> ClipIDGenerator::getClipIDs() const {
std::map<UnwrappedTileID, ClipID> clipIDs;
// Merge everything.
for (auto& pair : pool) {
auto& id = pair.first;
auto& leaf = pair.second;
auto res = clipIDs.emplace(id, leaf.clip);
if (!res.second) {
// Merge with the existing ClipID when there was already an element with the
// same tile ID.
res.first->second |= leaf.clip;
}
}
for (auto it = clipIDs.begin(); it != clipIDs.end(); ++it) {
auto& childId = it->first;
auto& childClip = it->second;
// Loop through all preceding stencils, and find all parents.
for (auto parentIt = std::reverse_iterator<decltype(it)>(it);
parentIt != clipIDs.rend(); ++parentIt) {
auto& parentId = parentIt->first;
if (childId.isChildOf(parentId)) {
// Once we have a parent, we add the bits that this ID hasn't set yet.
const auto& parentClip = parentIt->second;
const auto mask = ~(childClip.mask & parentClip.mask);
childClip.reference |= mask & parentClip.reference;
childClip.mask |= parentClip.mask;
}
}
}
// Remove tiles that are entirely covered by children.
util::erase_if(clipIDs, [&](const auto& stencil) {
return algorithm::coveredByChildren(stencil.first, clipIDs);
});
return clipIDs;
}
} // namespace algorithm
} // namespace mbgl

36
src/mbgl/algorithm/generate_clip_ids.hpp
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@@ -1,36 +0,0 @@
#pragma once
#include <mbgl/tile/tile_id.hpp>
#include <mbgl/util/clip_id.hpp>
#include <set>
#include <vector>
#include <map>
namespace mbgl {
namespace algorithm {
class ClipIDGenerator {
private:
struct Leaf {
Leaf(ClipID&);
void add(const CanonicalTileID &p);
bool operator==(const Leaf &other) const;
std::set<CanonicalTileID> children;
ClipID& clip;
};
uint8_t bit_offset = 0;
std::multimap<UnwrappedTileID, Leaf> pool;
public:
// The given vector must be sorted by id.
template <typename Renderable>
void update(std::vector<std::reference_wrapper<Renderable>> sortedRenderables);
std::map<UnwrappedTileID, ClipID> getClipIDs() const;
};
} // namespace algorithm
} // namespace mbgl

91
src/mbgl/algorithm/generate_clip_ids_impl.hpp
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@@ -1,91 +0,0 @@
#pragma once
#include <mbgl/algorithm/generate_clip_ids.hpp>
#include <mbgl/math/log2.hpp>
#include <mbgl/util/logging.hpp>
namespace mbgl {
namespace algorithm {
template <typename Renderable>
void ClipIDGenerator::update(std::vector<std::reference_wrapper<Renderable>> renderables) {
std::size_t size = 0;
assert(std::is_sorted(renderables.begin(), renderables.end(),
[](const Renderable& a, const Renderable& b) { return a.id < b.id; }));
const auto end = renderables.end();
for (auto it = renderables.begin(); it != end; ++it) {
auto& renderable = it->get();
if (!renderable.used || !renderable.needsClipping) {
continue;
}
renderable.clip = {};
Leaf leaf{ renderable.clip };
// Try to add all remaining ids as children. We sorted the tile list
// by z earlier, so all preceding items cannot be children of the current
// tile. We also compute the lower bound of the next wrap, because items of the next wrap
// can never be children of the current wrap.
auto child_it = std::next(it);
const auto children_end = std::lower_bound(
child_it, end, UnwrappedTileID{ static_cast<int16_t>(renderable.id.wrap + 1), { 0, 0, 0 } },
[](auto& a, auto& b) { return a.get().id < b; });
for (; child_it != children_end; ++child_it) {
auto& childTileID = child_it->get().id;
if (childTileID.isChildOf(it->get().id)) {
leaf.add(childTileID.canonical);
}
}
// Find a leaf with matching children.
for (auto its = pool.equal_range(renderable.id); its.first != its.second; ++its.first) {
auto& existing = its.first->second;
if (existing == leaf) {
leaf.clip = existing.clip;
break;
}
}
if (leaf.clip.reference.none()) {
// We haven't found an existing clip ID
size++;
}
pool.emplace(renderable.id, std::move(leaf));
}
if (size > 0) {
const uint32_t bit_count = util::ceil_log2(size + 1);
const std::bitset<8> mask = uint64_t(((1ul << bit_count) - 1) << bit_offset);
// We are starting our count with 1 since we need at least 1 bit set to distinguish between
// areas without any tiles whatsoever and the current area.
uint8_t count = 1;
for (auto& it : renderables) {
auto& renderable = it.get();
if (!renderable.used || !renderable.needsClipping) {
continue;
}
renderable.clip.mask |= mask;
// Assign only to clip IDs that have no value yet.
if (renderable.clip.reference.none()) {
renderable.clip.reference = uint32_t(count++) << bit_offset;
}
}
bit_offset += bit_count;
}
// Prevent this warning from firing on every frame,
// which can be expensive in some platforms.
static bool warned = false;
if (!warned && bit_offset > 8) {
Log::Error(Event::OpenGL, "stencil mask overflow");
warned = true;
}
}
} // namespace algorithm
} // namespace mbgl