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#pragma once
#include "glArrays.h"
#include <iterator>
#include <span>
#include <special_members.hpp>
#include <utility>
#include <vector>
template<typename T> class InstanceVertices {
public:
InstanceVertices(size_t initialSize = 16) : data {allocBuffer(buffer, initialSize)}, next {} { }
~InstanceVertices()
{
glUnmapNamedBuffer(buffer);
}
class InstanceProxy {
public:
InstanceProxy(InstanceVertices * iv, std::size_t idx) : instances {iv}, index {idx} { }
InstanceProxy(InstanceProxy && other) : instances {std::exchange(other.instances, nullptr)}, index {other.index}
{
}
NO_COPY(InstanceProxy);
~InstanceProxy()
{
if (instances) {
instances->release(*this);
}
}
InstanceProxy &
operator=(InstanceProxy && other)
{
instances = std::exchange(other.instances, nullptr);
index = other.index;
}
operator T &()
{
return *get();
}
operator const T &() const
{
return *get();
}
template<typename U>
T &
operator=(U && v)
{
return instances->data[index] = std::forward<U>(v);
}
T *
get()
{
return &instances->data[index];
}
const T *
get() const
{
return &instances->data[index];
}
T *
operator->()
{
return get();
}
const T *
operator->() const
{
return get();
}
T &
operator*()
{
return *get();
}
const T &
operator*() const
{
return *get();
}
private:
friend InstanceVertices;
InstanceVertices<T> * instances;
std::size_t index;
};
template<typename... Params>
InstanceProxy
acquire(Params &&... params)
{
if (!unused.empty()) {
auto idx = unused.back();
unused.pop_back();
new (&data[idx]) T(std::forward<Params>(params)...);
return InstanceProxy {this, idx};
}
if (next >= data.size()) {
resize(data.size() * 2);
}
new (&data[next]) T(std::forward<Params>(params)...);
return InstanceProxy {this, next++};
}
void
release(const InstanceProxy & p)
{
data[p.index].~T();
unused.push_back(p.index);
}
protected:
friend InstanceProxy;
static std::span<T>
allocBuffer(const glBuffer & buffer, std::size_t count)
{
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, static_cast<GLsizeiptr>(sizeof(T) * count), nullptr, GL_DYNAMIC_DRAW);
auto data = static_cast<T *>(glMapNamedBuffer(buffer, GL_READ_WRITE));
glBindBuffer(GL_ARRAY_BUFFER, 0);
return {data, count};
}
void
resize(size_t newCapacity)
{
const auto maintain = std::min(newCapacity, data.size());
const auto maintaind = static_cast<typename decltype(data)::difference_type>(maintain);
std::vector<T> existing;
existing.reserve(maintain);
std::move(data.begin(), data.begin() + maintaind, std::back_inserter(existing));
data = allocBuffer(buffer, newCapacity);
std::move(existing.begin(), existing.begin() + maintaind, data.begin());
}
glBuffer buffer;
std::span<T> data;
std::size_t next;
std::vector<size_t> unused;
};
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