我有一个glm::vec3
数组count * 3
元素。我有另一个数组,其中包含要复制的元素的int
个索引。一个例子:
thrust::device_vector<glm::vec3> vals(9);
// vals contains 9 vec3, which represent 3 "items"
// vals[0], vals[1], vals[2] are the first "item",
// vals[3], vals[4], vals[5] are the second "item"...
int idcs[] = {0, 2};
// index 0 and 2 should be copied, i.e.
// vals[0..2] and vals[6..8]
我尝试使用置换迭代器,但我无法使用它。我的方法是:
thrust::copy(
thrust::make_permutation_iterator(vals, idcs),
thrust::make_permutation_iterator(vals, idcs + 2),
target.begin()
);
但当然这只会复制vals[0]
和vals[2]
而不是vals[0] vals[1] vals[2]
和vals[6] vals[7] vals[8]
。
是否可以使用Thrust将所需的值从一个缓冲区复制到另一个缓冲区?
答案 0 :(得分:3)
我们可以将strided ranges的想法与您的permutation iterator方法相结合,以实现您想要的目标。
基本思想是使用你的置换迭代器方法来选择要复制的项目的“组”,我们将使用一组3个跨步范围迭代器组合成一个zip迭代器来选择每组中的3个项目。我们需要一个用于输入的zip迭代器和一个用于输出的zip迭代器。以下是一个功能齐全的示例,使用uint3
作为glm::vec3
的代理:
$ cat t484.cu
#include <vector_types.h>
#include <thrust/device_vector.h>
#include <thrust/host_vector.h>
#include <iostream>
#include <thrust/copy.h>
#include <thrust/iterator/permutation_iterator.h>
#include <thrust/iterator/counting_iterator.h>
#include <thrust/iterator/transform_iterator.h>
#include <thrust/functional.h>
#define DSIZE 18
template <typename Iterator>
class strided_range
{
public:
typedef typename thrust::iterator_difference<Iterator>::type difference_type;
struct stride_functor : public thrust::unary_function<difference_type,difference_type>
{
difference_type stride;
stride_functor(difference_type stride)
: stride(stride) {}
__host__ __device__
difference_type operator()(const difference_type& i) const
{
return stride * i;
}
};
typedef typename thrust::counting_iterator<difference_type> CountingIterator;
typedef typename thrust::transform_iterator<stride_functor, CountingIterator> TransformIterator;
typedef typename thrust::permutation_iterator<Iterator,TransformIterator> PermutationIterator;
// type of the strided_range iterator
typedef PermutationIterator iterator;
// construct strided_range for the range [first,last)
strided_range(Iterator first, Iterator last, difference_type stride)
: first(first), last(last), stride(stride) {}
iterator begin(void) const
{
return PermutationIterator(first, TransformIterator(CountingIterator(0), stride_functor(stride)));
}
iterator end(void) const
{
return begin() + ((last - first) + (stride - 1)) / stride;
}
protected:
Iterator first;
Iterator last;
difference_type stride;
};
typedef thrust::device_vector<uint3>::iterator Iter;
int main(){
// set up test data
int idcs[] = {0, 2, 5};
unsigned num_idcs = sizeof(idcs)/sizeof(int);
thrust::host_vector<uint3> h_vals(DSIZE);
for (int i = 0; i < DSIZE; i ++) {
h_vals[i].x = i;
h_vals[i].y = 100+i;
h_vals[i].z = 1000+i;}
thrust::device_vector<uint3> d_target(num_idcs*3);
thrust::host_vector<int> h_idcs(idcs, idcs + num_idcs);
thrust::device_vector<int> d_idcs = h_idcs;
thrust::device_vector<uint3> d_vals = h_vals;
// set up strided ranges for input, output
strided_range<Iter> item_1(d_vals.begin() , d_vals.end(), 3);
strided_range<Iter> item_2(d_vals.begin()+1, d_vals.end(), 3);
strided_range<Iter> item_3(d_vals.begin()+2, d_vals.end(), 3);
// set up strided ranges for output
strided_range<Iter> out_1(d_target.begin() , d_target.end(), 3);
strided_range<Iter> out_2(d_target.begin()+1, d_target.end(), 3);
strided_range<Iter> out_3(d_target.begin()+2, d_target.end(), 3);
// copy from input to output
thrust::copy(thrust::make_permutation_iterator(thrust::make_zip_iterator(thrust::make_tuple(item_1.begin(), item_2.begin(), item_3.begin())), d_idcs.begin()), thrust::make_permutation_iterator(thrust::make_zip_iterator(thrust::make_tuple(item_1.begin(), item_2.begin(), item_3.begin())), d_idcs.end()), thrust::make_zip_iterator(thrust::make_tuple(out_1.begin(), out_2.begin(), out_3.begin())));
// print out results
thrust::host_vector<uint3> h_target = d_target;
for (int i = 0; i < h_target.size(); i++)
std::cout << "index: " << i << " x: " << h_target[i].x << " y: " << h_target[i].y << " z: " << h_target[i].z << std::endl;
return 0;
}
$ nvcc -arch=sm_20 -o t484 t484.cu
$ ./t484
index: 0 x: 0 y: 100 z: 1000
index: 1 x: 1 y: 101 z: 1001
index: 2 x: 2 y: 102 z: 1002
index: 3 x: 6 y: 106 z: 1006
index: 4 x: 7 y: 107 z: 1007
index: 5 x: 8 y: 108 z: 1008
index: 6 x: 15 y: 115 z: 1015
index: 7 x: 16 y: 116 z: 1016
index: 8 x: 17 y: 117 z: 1017
$