[英]Attempting to implement a C++ library, need some pointers on how to interface with it
我在 C++ 方面相對缺乏經驗,正在嘗試將庫編譯為 DLL 以在 Unity 中使用。 至於生成 DLL 並與之交互,我已經成功地讓我的下面的函數在 Unity 中調用並返回一個虛擬值,不用擔心。
我正在努力解決如何與這個Approximate Nearest Neighbor庫交互,並且可以使用一些指針。 (如果不下載上面鏈接的源代碼並自己查看,這可能是一個很難定義的問題,但我會盡量簡化它)
在 Unity 中,我有一個三維數組(points[] = float[x,y,z])和一個空間中的查詢點(float[x,y,z])。 我希望將這些數據輸入到類似於下面的函數中(我已經從 ann_sample.cpp 中修改了 - 原始鏈接在底部),並將最近的鄰居返回到這一點。
我的功能
int myInit(float x, float y, float z, int numPoints, int maxPoints, int nn)
{
int nPts;
ANNpointArray dataPts;
ANNpoint queryPt;
ANNidxArray nnIdx;
ANNdistArray dists;
ANNkd_tree* kdTree;
int dimension = 3;
queryPt = annAllocPt(dimension , x); //This only expects the dimension, and a coord - I assume this is pre-allocation?
dataPts = annAllocPts(maxPoints, dimension); //Again, this does not expect the coordinate (xyz) data, is pre-allocating the array?
nnIdx = new ANNidx[nn]; // more pre-allocating?
dists = new ANNdist[nn]; // more pre-allocating?
nPts = numPoints;
//Should we be populating the actual queryPt and dataPts here?
//at the moment, these are still empty?
kdTree = new ANNkd_tree( // build search structure
dataPts, // the data points
nPts, // number of points
dimension); // dimension of space
kdTree->annkSearch( // search
queryPt, // query point
nn, // number of near neighbors
nnIdx, // nearest neighbors (returned)
dists, // distance (returned)
eps); // error bound
annClose(); // done with ANN
return nnIdx[0]; //this is the nearest neighbor
}
原始函數(這是一個命令行輸入 - 即 ann_sample [-d dim] [-max mpts] [-nn k] [-e eps] [-df data] [-qf query])
int main(int argc, char **argv)
{
int nPts; // actual number of data points
ANNpointArray dataPts; // data points
ANNpoint queryPt; // query point
ANNidxArray nnIdx; // near neighbor indices
ANNdistArray dists; // near neighbor distances
ANNkd_tree* kdTree; // search structure
getArgs(argc, argv); // read command-line arguments
queryPt = annAllocPt(dim); // allocate query point
dataPts = annAllocPts(maxPts, dim); // allocate data points
nnIdx = new ANNidx[k]; // allocate near neigh indices
dists = new ANNdist[k]; // allocate near neighbor dists
nPts = 0; // read data points
cout << "Data Points:\n";
while (nPts < maxPts && readPt(*dataIn, dataPts[nPts])) {
printPt(cout, dataPts[nPts]);
nPts++;
}
kdTree = new ANNkd_tree( // build search structure
dataPts, // the data points
nPts, // number of points
dim); // dimension of space
while (readPt(*queryIn, queryPt)) { // read query points
cout << "Query point: "; // echo query point
printPt(cout, queryPt);
kdTree->annkSearch( // search
queryPt, // query point
k, // number of near neighbors
nnIdx, // nearest neighbors (returned)
dists, // distance (returned)
eps); // error bound
cout << "\tNN:\tIndex\tDistance\n";
for (int i = 0; i < k; i++) { // print summary
dists[i] = sqrt(dists[i]); // unsquare distance
cout << "\t" << i << "\t" << nnIdx[i] << "\t" << dists[i] << "\n";
}
}
delete [] nnIdx; // clean things up
delete [] dists;
delete kdTree;
annClose(); // done with ANN
return EXIT_SUCCESS;
}
正如您在我的評論中看到的那樣,我無法確定實際輸入數據的位置和方式,即 - 上面提到的我的點數組。
通過使用“istream”類,似乎正在使用以下代碼填充數據(在參考函數中),但我不明白這是如何工作的,或者我將如何模擬它。
while (nPts < maxPts && readPt(*dataIn, dataPts[nPts])) {
printPt(cout, dataPts[nPts]);
nPts++;
}
...
bool readPt(istream &in, ANNpoint p) // read point (false on EOF)
{
for (int i = 0; i < dim; i++) {
if(!(in >> p[i])) return false;
}
return true;
}
更新:
把這一切寫出來顯然是我在正確方向上需要的推動力! 如果它與未來的任何人相關,我與它交互的方式是相當簡單的。
我將一些 2D 數組傳遞到 C++ 插件中,然后將其轉換為 ANNpointArrays。 鑒於它是 C++,我需要首先實例化適當大小的數組,然后填充如下:
float qPoints[][3]
.....
for (int i = 0; i < nQueryPts; i++) {
for (int j = 0; j < dimension; j++)
{
queryPts[i][j] = qPoints[i][j];
}
}
一旦我有了這個,在我的每個查詢點上運行一個 annKSearch 就相對簡單了,返回一個最近鄰的整數數組,並浮動距離。 我需要學習一些關於如何在 C++ 中傳遞和實例化數組的知識,但這比我想象的要容易得多!
並不是說有人在讀它——但這對我來說是一個有用的練習,我把這個問題留了下來,以防其他人試圖用 C# 實現這個庫!
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