图片旋转算法

本文为转载文章，但是希望更多的朋友来优化该算法。

转载地址：http://www.cnblogs.com/ice6/archive/2010/08/19/rotating-an-image-in-silverlight-without-cropping.html

旋转算法如下：

Rotation[degrees counterclockwise]	Subscript Manipulation using Pixels
0	Out[i, j] = In[i, j]
90	Out[j, Right-i-1] = In[i, j]
180	Out[Right-i-1, Bottom-j-1] = In[i, j]
270	Out[Bottom-j-1,i] = In[i, j]

i代表x轴的值，j代表Y轴上的值

  private WriteableBitmap WBRotate(WriteableBitmap wb, int CounterclockwiseAngle)

  {

      int [,] wb_arr = new int [wb.PixelWidth, wb.PixelHeight];

      //导致许多缺页中断的初始化循环

      //for (int r = 0; r < wb.PixelHeight; r++)// r=row    c=column

      //{

      //    for (int c = 0; c < wb.PixelWidth; c++)

      //    {

      //        wb_arr[c, r] = wb.Pixels[wb.PixelWidth * r + c];

      //    }

      //}

      //导致较少缺页中断的初始化循环 对上面代码的简单优化

      for ( int c = 0; c < wb.PixelWidth; c++) // r=row    c=column

      {

          for ( int r = 0; r < wb.PixelHeight; r++)

          {

              wb_arr[c, r] = wb.Pixels[wb.PixelWidth * r + c];

          }

      }

 

      WriteableBitmap wb2;

      int [,] wb_arr_2;

 

      if (CounterclockwiseAngle == 0 || CounterclockwiseAngle == 360 || CounterclockwiseAngle == -360) //0度 360度

      {

          wb2 = new WriteableBitmap(wb.PixelWidth, wb.PixelHeight);

          wb_arr_2 = new int [wb.PixelWidth, wb.PixelHeight];

          wb_arr_2 = wb_arr;

      }

      else if (CounterclockwiseAngle == 90 || CounterclockwiseAngle == -270) //90 -270//Math.Sin(

      {

          wb2 = new WriteableBitmap(wb.PixelHeight, wb.PixelWidth);

          wb_arr_2 = new int [wb.PixelHeight, wb.PixelWidth];

          for ( int c = 0; c < wb_arr.GetLength(0); c++) //width  i

          {

              for ( int r = 0; r < wb_arr.GetLength(1); r++) //height j

              {

                  wb_arr_2[r, wb_arr.GetLength(0) - c - 1] = wb_arr[c, r]; //90 Out[j, Right-i-1] = In[i, j]  Right代表真个宽度

              }

          }

      }

      else if (CounterclockwiseAngle == 180 || CounterclockwiseAngle == -180) //180 -180

      {

          wb2 = new WriteableBitmap(wb.PixelWidth, wb.PixelHeight);

          wb_arr_2 = new int [wb.PixelWidth, wb.PixelHeight];

          for ( int c = 0; c < wb_arr.GetLength(0); c++) //width  i

          {

              for ( int r = 0; r < wb_arr.GetLength(1); r++) //height j

              {

                  wb_arr_2[wb_arr.GetLength(0) - c - 1, wb_arr.GetLength(1) - r - 1] = wb_arr[c, r]; //180 Out[Right-i-1, Bottom-j-1] = In[i, j] 

              }

          }

      }

      else if (CounterclockwiseAngle == 270 || CounterclockwiseAngle == -90) //270 -90

      {

          wb2 = new WriteableBitmap(wb.PixelHeight, wb.PixelWidth);

          wb_arr_2 = new int [wb.PixelHeight, wb.PixelWidth];

          for ( int c = 0; c < wb_arr.GetLength(0); c++) //width  i

          {

              for ( int r = 0; r < wb_arr.GetLength(1); r++) //height j

              {

                  wb_arr_2[wb_arr.GetLength(1) - r - 1, c] = wb_arr[c, r]; //270 Out[Bottom-j-1,i] = In[i, j]

              }

          }

      }

      else

      {

          return null ; //如果是其他角度 就直接返回null

      }

      //将二位数组转换成Pixels

      for ( int r = 0; r < wb_arr_2.GetLength(1); r++) // r=row    c=column

      {

          for ( int c = 0; c < wb_arr_2.GetLength(0); c++)

          {

              wb2.Pixels[wb2.PixelWidth * r + c] = wb_arr_2[c, r];

          }

      }

      return wb2;

  }