上兩節課都是對一個數組進行處理。這節我們來個有意思的。同樣是旋轉。但我們旋轉的對象是張（２５６*２５６）的圖片。圖片旋轉４５度，旋轉后大小還是２５６*２５６，超出部份進行剪除。

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圖片旋轉處理有個特別的地方。buf_A是存儲源圖數據（R,G,B顏色分量）,buf_B是存儲旋轉后數據。我們不能簡單將buf_A中的數據直接計算旋轉后位置。而是遍歷buf_B每個數據，計算那些數據旋轉后存在這個位置的數據他在buf_A的坐標是多少。為什么呢？不是因為不能直接旋轉。而是因為坐標是整數型。進行旋轉計算后會得出浮點數，有小數。計算精度不同。如果還用直接旋轉計算方法。成出的位圖將會出現斑點。大家可試下。

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我們來看源碼

rotate.cl源碼

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__kernel void rotation(__global int* A, ????????????????????__global int* B, ????????????????????int width, ????????????????????int height, ????????????????????float sinangle, ????????????????????float cosangle) { ????//獲取索引號，這里是二維的，所以可以取兩個 ????//否則另一個永遠是0 ????int col = get_global_id(0); ????int row = get_global_id(1); ????//計算圖形中心點 ????float cx = ((float)width)/2; ????float cy = ((float)height)/2; ????int nx = (int)(cx + cosangle * ((float)col-cx) + sinangle * ((float)row-cy)); ????int ny = (int)(cy + (-1*sinangle) * ((float)col-cx) + cosangle * ((float)row-cy)); ????//邊界檢測 ????if(nx>=0 && nx<width && ny>=0 && ny<height) ????{ ????????B[col*3+0+row*width*3] = A[nx*3+0+ny*width*3]; ????????B[col*3+1+row*width*3] = A[nx*3+1+ny*width*3]; ????????B[col*3+2+row*width*3] = A[nx*3+2+ny*width*3]; ????} }

main.cpp源碼

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#include <iostream> #include <stdio.h> #include <string.h> #include <string> #include <conio.h> #include <math.h>//數學庫 #include <CL/cl.h>//包含CL的頭文件 //調用freeimage #include <freeimage.h> using namespace std; //8x8數組 const int dim_x = 256; const int dim_y = 256; //45度的弧度 const float angle = 3.1415926f/4.0f; static int buf_A[dim_x*dim_y*3]; static int buf_B[dim_x*dim_y*3]; //加載圖片 //以RGBA格式存儲圖片 static bool LoadImg(const char* fname) { ????//初始化FreeImage ????FreeImage_Initialise(TRUE); ????//定義圖片格式為未知 ????FREE_IMAGE_FORMAT fif = FIF_UNKNOWN; ????//獲取圖片格式 ????fif = FreeImage_GetFileType(fname,0); ????//根據獲取格式讀取圖片數據 ????FIBITMAP* bitmap = FreeImage_Load(fif,fname,0); ????if(!bitmap) ????{ ????????printf("load error!\n"); ????????return false; ????} ????int x,y; ????RGBQUAD m_rgb; ????//獲取圖片長寬 ????int width = (int)FreeImage_GetWidth(bitmap); ????int height = (int)FreeImage_GetHeight(bitmap); ????//獲取圖片數據 ????//按RGBA格式保存到數組中 ????for(y=0;y<height;y++) ????{ ????????for(x=0;x<width;x++) ????????{ ????????????//獲取像素值 ????????????FreeImage_GetPixelColor(bitmap,x,y,&m_rgb); ????????????//將RGB值存入數組 ????????????buf_A[y*width*3+x*3+2] = m_rgb.rgbRed; ????????????buf_A[y*width*3+x*3+1] = m_rgb.rgbGreen; ????????????buf_A[y*width*3+x*3+0] = m_rgb.rgbBlue; ????????} ????} ????FreeImage_Unload(bitmap); ????return true; } static bool SaveImg() { ????//初始化FreeImage ????FreeImage_Initialise(TRUE); ????FIBITMAP* bitmap =FreeImage_Allocate(dim_x,dim_y,32,8,8,8); ????int m,n; ????for(n=0;n<dim_y;n++) ????{ ????????BYTE *bits =FreeImage_GetScanLine(bitmap,n); ????????for(m=0;m<dim_x;m++) ????????{ ????????????bits[0] = buf_B[dim_x*3*n+m*3+0]; ????????????bits[1] = buf_B[dim_x*3*n+m*3+1]; ????????????bits[2] = buf_B[dim_x*3*n+m*3+2]; ????????????bits[3] = 255; ????????????bits+=4; ????????} ????} ????//保存圖片為PNG格式 ????if(false ==FreeImage_Save(FIF_PNG, bitmap,"rotate.png", PNG_DEFAULT)) ????{ ????????printf("save image error\n"); ????} ????FreeImage_Unload(bitmap); ????return true; } //從外部文件獲取cl內核代碼 bool GetFileData(const char* fname,string& str) { ????FILE* fp = fopen(fname,"r"); ????if(fp==NULL) ????{ ????????printf("no found file\n"); ????????return false; ????} ????while(feof(fp)==0) ????{ ????????str += fgetc(fp); ????} ????return true; } int main() { ????if(LoadImg("bk.png")==false) ????{ ????????printf("error load bk.png!\n"); ????????return 0; ????} ????//先讀外部CL核心代碼，如果失敗則退出。 ????//代碼存buf_code里面 ????string code_file; ????if(false == GetFileData("rotate.cl",code_file)) ????{ ????????printf("Open rotate.cl error\n"); ????????return 0; ????} ????char* buf_code = new char[code_file.size()]; ????strcpy(buf_code,code_file.c_str()); ????buf_code[code_file.size()-1] = NULL; ????//聲明CL所需變量。 ????cl_device_id device; ????cl_platform_id platform_id = NULL; ????cl_context context; ????cl_command_queue cmdQueue; ????cl_mem bufferA,bufferB; ????cl_program program; ????cl_kernel kernel = NULL; ????//我們使用的是二維向量 ????//設定向量大小（維數） ????size_t globalWorkSize[2]; ????globalWorkSize[0] = dim_x; ????globalWorkSize[1] = dim_y; ????cl_int err; ????/* ????????定義輸入變量和輸出變量，并設定初值 ????*/ ????size_t datasize = sizeof(int) * dim_x * dim_y * 3; ????//step 1:初始化OpenCL ????err = clGetPlatformIDs(1,&platform_id,NULL); ????if(err!=CL_SUCCESS) ????{ ????????cout<<"clGetPlatformIDs error:"<<err<<endl; ????????return 0; ????} ????//這次我們只用CPU來進行并行運算，當然你也可以該成GPU ????clGetDeviceIDs(platform_id,CL_DEVICE_TYPE_CPU,1,&device,NULL); ????//step 2:創建上下文 ????context = clCreateContext(NULL,1,&device,NULL,NULL,NULL); ????//step 3:創建命令隊列 ????cmdQueue = clCreateCommandQueue(context,device,0,NULL); ????//step 4:創建數據緩沖區 ????bufferA = clCreateBuffer(context, ?????????????????????????????CL_MEM_READ_ONLY, ?????????????????????????????datasize,NULL,NULL); ????bufferB = clCreateBuffer(context, ?????????????????????????????CL_MEM_WRITE_ONLY, ?????????????????????????????datasize,NULL,NULL); ????//step 5:將數據上傳到緩沖區 ????clEnqueueWriteBuffer(cmdQueue, ?????????????????????????bufferA,CL_FALSE, ?????????????????????????0,datasize, ?????????????????????????buf_A,0, ?????????????????????????NULL,NULL); ????//step 6:加載編譯代碼,創建內核調用函數 ????program = clCreateProgramWithSource(context,1, ????????????????????????????????????????(const char**)&buf_code, ????????????????????????????????????????NULL,NULL); ????clBuildProgram(program,1,&device,NULL,NULL,NULL); ????kernel = clCreateKernel(program,"rotation",NULL); ????//step 7:設置參數，執行內核 ????float sinangle = sinf(angle); ????float cosangle = cosf(angle); ????clSetKernelArg(kernel,0,sizeof(cl_mem),&bufferA); ????clSetKernelArg(kernel,1,sizeof(cl_mem),&bufferB); ????clSetKernelArg(kernel,2,sizeof(cl_int),&dim_x); ????clSetKernelArg(kernel,3,sizeof(cl_int),&dim_y); ????clSetKernelArg(kernel,4,sizeof(cl_float),&sinangle); ????clSetKernelArg(kernel,5,sizeof(cl_float),&cosangle); ????//注意這里第三個參數已經改成2，表示二維數據。 ????clEnqueueNDRangeKernel(cmdQueue,kernel, ???????????????????????????2,NULL, ???????????????????????????globalWorkSize, ???????????????????????????NULL,0,NULL,NULL); ????//step 8:取回計算結果 ????clEnqueueReadBuffer(cmdQueue,bufferB,CL_TRUE,0, ????????????????????????datasize,buf_B,0,NULL,NULL); ????SaveImg(); ????//釋放所有調用和內存 ????clReleaseKernel(kernel); ????clReleaseProgram(program); ????clReleaseCommandQueue(cmdQueue); ????clReleaseMemObject(bufferA); ????clReleaseMemObject(bufferB); ????clReleaseContext(context); ????delete buf_code; ????return 0; }

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源圖

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旋轉后圖

總結

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