基于GPU的粒子系統(tǒng)的粒子數(shù)目一般等于stream output的圖元數(shù)，而stream output的統(tǒng)計(jì)信息可以通過ID3D10Query接口獲取。步驟如下：
1.創(chuàng)建ID3D10Query查詢對(duì)象
1
ID3D10Query* pQuery;
2D3D10_QUERY_DESC queryDesc;
3queryDesc.Query = D3D10_QUERY_SO_STATISTICS;
4queryDesc.MiscFlags = 0;
5pD3DDevice->CreateQuery( &queryDesc, &pQuery );
2.在用DrawAuto()繪制粒子處設(shè)置查詢的開始和結(jié)束標(biāo)記：
1 pQuery->Begin();
2 pD3DDevice->DrawAuto(); // 繪制粒子
3 pQuery->End();
3. 獲取Stream Output輸出的圖元個(gè)數(shù)：
1 D3D10_QUERY_DATA_SO_STATISTICS streamOutBufferSize;
2 if ( S_OK == pQuery->GetData( &streamOutBufferSize, pQuery->GetDataSize(), 0 ) ) // 錯(cuò)誤產(chǎn)生的原因
3 {
4 mStreamOutParticleSize = (unsigned)streamOutBufferSize.NumPrimitivesWritten;
5 }
可是試驗(yàn)的時(shí)候，發(fā)現(xiàn)獲取的粒子數(shù)目不正確。調(diào)試后發(fā)現(xiàn)
ID3D10Query::GetData()總返回S_FALSE，但極少數(shù)情況下也返回S_OK。參考文獻(xiàn)1后明白，ID3D10Query接口是異步從GPU獲取數(shù)據(jù)的,當(dāng)GPU中繁忙或者查詢的數(shù)據(jù)沒有準(zhǔn)備好，就會(huì)返回S_FALSE。正確的做法是：如果ID3D10Query::GetData()返回失敗，則繼續(xù)查詢，直到成功為止。正確的完整代碼如下：
1 // 創(chuàng)建ID3D10Query查詢對(duì)象
2 ID3D10Query* pQuery;
3 D3D10_QUERY_DESC queryDesc;
4 queryDesc.Query = D3D10_QUERY_SO_STATISTICS;
5 queryDesc.MiscFlags = 0;
6 pD3DDevice->CreateQuery( &queryDesc, &pQuery );
7
8 // 設(shè)置查詢的開始和結(jié)束標(biāo)志
9 pQuery->Begin();
10 pD3DDevice->DrawAuto();
11 pQuery->End();
12
13 // 獲取stream output輸出的圖元個(gè)數(shù)
14 D3D10_QUERY_DATA_SO_STATISTICS streamOutBufferSize;
15 while ( S_OK != pQuery->GetData( &streamOutBufferSize, pQuery->GetDataSize(), 0 ) ); // 不停循環(huán)，直到成功
16 mStreamOutParticleSize = (unsigned)streamOutBufferSize.NumPrimitivesWritten;
參考資料：
1. Get streaming output statistics: http://www.bennychen.cn/2009/07/get-streaming-output-statistics/