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            羅朝輝(飄飄白云)

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            Android 上實現(xiàn)水波特效二--優(yōu)化   

            羅朝輝(http://www.shnenglu.com/kesalin

            轉(zhuǎn)載請注明出處

                在上一篇文章《Android 上實現(xiàn)水波特效中對水波波幅的計算是針對每一個像素的,效率比較低,尤其是在手機(jī)上運行,相當(dāng)緩慢。我們可以利用線性插值進(jìn)行優(yōu)化,這樣可以將計算減少一半(MeshSize 2)或減少四分之三(MeshSize 4),效率得以大大提升,即使是在水機(jī)上也能較為流暢地運行。

             

            在下面的代碼中,為了充分使用移位運算替代乘除法,MeshSize 必須為 2 的整次冪,MeshShift 就是其冪數(shù),表示計算時的移位位數(shù)。代碼下載鏈接:http://www.shnenglu.com/Files/kesalin/RippleDemo_opt.zip

             

            線性插值優(yōu)化之后的水波擴(kuò)散代碼如下:

             

            static final int MeshSize = 2;

            static final int MeshShift = 1;  

            int m_meshWidth;

            int m_meshHeight;

            m_meshWidth = m_width / MeshSize + 1;

            m_meshHeight = m_height / MeshSize + 1;;

             

            void rippleSpread()

            {

            m_waveFlag = false;

             

            int i = 0, offset = 0;

            for (int y = 1; y < m_meshHeight - 1; ++y) {

            offset = y * m_meshWidth;

            for (int x = 1; x < m_meshWidth - 1; ++x) {

            i = offset + x;

            m_buf2[i] = (short)(((m_buf1[i - 1] + m_buf1[i + 1]

                                + m_buf1[i - m_meshWidth]

                                + m_buf1[i + m_meshWidth]) >> 1) - m_buf2[i]);

             

                        m_buf2[i] -= (m_buf2[i] >> 5);

                        m_waveFlag |= (m_buf2[i] != 0);

                   }

                }

               

               if (m_waveFlag){

                   m_waveFlag = false;

                  

                   for (int y = 1; y < m_meshHeight - 1; ++y) {

                      offset = y * m_meshWidth;

                      for (int x = 1; x < m_meshWidth - 1; ++x) {

                         i = offset + x;

                         m_bufDiffX[i] = (short)((m_buf2[i + 1] - m_buf2[i - 1]) >> 3);

                         m_bufDiffY[i] = (short)((m_buf2[i + m_meshWidth] - m_buf2[i - m_meshWidth]) >> 3);

                        

                         m_waveFlag |= (m_bufDiffX[i] != 0 || m_bufDiffY[i] != 0);

                      }

                   }

               }

              

               //交換波能數(shù)據(jù)緩沖區(qū)

               short[] temp = m_buf1;

                m_buf1 = m_buf2;

               m_buf2 = temp;

            }

                  

            既然波幅計算使用了線性插值,描繪時的代碼也許相應(yīng)進(jìn)行更改:

             

            Point p1, p2, p3, p4;

            Point pRowStart, pRowEnd, p, rowStartInc, rowEndInc, pInc;

             

            void rippleRender()

            { 

               int px = 0, py = 0, dx = 0, dy = 0;

               int index = 0, offset = 0;

              

               for (int j = 1; j < m_meshHeight; ++j) {

                  offset = j * m_meshWidth;

                  for (int i = 1; i < m_meshWidth; ++i) {    

                     index = offset + i;

                     p1.x = m_bufDiffX[index - m_meshWidth - 1];

                     p1.y = m_bufDiffY[index - m_meshWidth - 1];

                     p2.x = m_bufDiffX[index - m_meshWidth];

                     p2.y = m_bufDiffY[index - m_meshWidth];

                     p3.x = m_bufDiffX[index - 1];

                     p3.y = m_bufDiffY[index - 1];

                     p4.x = m_bufDiffX[index];

                     p4.y = m_bufDiffY[index];

                    

                     pRowStart.x = p1.x << MeshShift;

                     pRowStart.y = p1.y << MeshShift;

                     rowStartInc.x = p3.x - p1.x;

                     rowStartInc.y = p3.y - p1.y;

                    

                     pRowEnd.x = p2.x << MeshShift;

                     pRowEnd.y = p2.y << MeshShift;

                     rowEndInc.x = p4.x - p2.x;

                     rowEndInc.y = p4.y - p2.y;

             

                     py = (j - 1) << MeshShift;

                     for (int y = 0; y < MeshSize; ++y) {

                        p.x = pRowStart.x;

                        p.y = pRowStart.y;

                       

                        // scaled by MeshSize times

                        pInc.x = (pRowEnd.x - pRowStart.x) >> MeshShift;

                        pInc.y = (pRowEnd.y - pRowStart.y) >> MeshShift;

                       

                        px = (i - 1) << MeshShift;

                         for (int x = 0; x < MeshSize; ++x) {

                            dx = px + p.x >> MeshShift;

                            dy = py + p.y >> MeshShift;

                           

                            if ((dx >= 0) && (dy >= 0) && (dx < m_width) && (dy < m_height) ) {

                                m_bitmap2[py * m_width + px] = m_bitmap1[dy * m_width + dx];

                             }

                             else {

                                m_bitmap2[py * m_width + px] = m_bitmap1[py * m_width + px];

                             }

             

                             p.x += pInc.x;

                             p.y += pInc.y;

                             ++px;

                         }

                        

                         pRowStart.x += rowStartInc.x;

                         pRowStart.y += rowStartInc.y;

                         pRowEnd.x += rowEndInc.x;

                         pRowEnd.y += rowEndInc.y;

                         ++py;

                     }

                  }

               }

            }

             

            posted on 2010-09-28 11:49 羅朝輝 閱讀(1418) 評論(0)  編輯 收藏 引用 所屬分類: 計算機(jī)圖形學(xué)移動開發(fā)Algorithms
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