Android 上實現水波特效二--優化
羅朝輝(http://www.shnenglu.com/kesalin)
轉載請注明出處
在上一篇文章《Android 上實現水波特效》中對水波波幅的計算是針對每一個像素的,效率比較低,尤其是在手機上運行,相當緩慢。我們可以利用線性插值進行優化,這樣可以將計算減少一半(MeshSize 為 2)或減少四分之三(MeshSize 為 4),效率得以大大提升,即使是在水機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,表示計算時的移位位數。代碼下載鏈接:http://www.shnenglu.com/Files/kesalin/RippleDemo_opt.zip
線性插值優化之后的水波擴散代碼如下:
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); } } } //交換波能數據緩沖區 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進行更改:
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; } } } } |