此函数用于生成GeoMipMap地形算法的索引Buffer，可以生成一个由参数指定的特定Patch的所引数据，生成的几何体为三角形条带，生成三角形中有部分退化三角形，用于三角形条带的连接。生成的三角形是CCW或者CW一致的。
pIndex ：指向索引Buffer当前填充位置
wWidth ：Patch的大小，取值范围9，17，33......
wLevel ：Lod级别，取值范围0，1，2，3......，数字越小细节级越高，0为最高细节级
bUp，bDown，bLeft，bRight：上下左右四个方向是否连接低细节级Patch
返回值 ：返回填充的索引数据个数，由于生成的是三角形条带，实际生成的三角形数目为返回值减2
int GenerateStripIndex(WORD* pIndex, WORD wWidth, WORD wLevel,
bool bUp,
bool bDown,
bool bLeft,
bool bRight)
{
WORD i, j; WORD w1, w2; WORD wPower = 1; for( i=0; i<wLevel; i++ ) wPower *= 2; WORD wGridWdith = (wWidth - 1) / wPower; WORD wPitch = wGridWdith * 2 + 4; WORD *p = pIndex; w1 = 0; for( j=0; j < wGridWdith / 2; j++ )
{
w2 = w1 + wWidth * wPower; for( i=0; i < wGridWdith; i++) {
*p++ = w1; *p++ = w2; w1 += wPower; w2 += wPower;
} *p++ = w1; *p++ = w2, *p++ = w2, *p++ = w2; w1 = w2 + wWidth * wPower; for( i=0; i < wGridWdith; i++) {
*p++ = w1; *p++ = w2; w1 -= wPower; w2 -= wPower; } *p++ = w1; *p++ = w2, *p++ = w1, *p++ = w1; } if( bDown ) {
p = pIndex + 2; for( i=0; i<wGridWdith / 2; i++) {
(*p) -= wPower; p += 4; } } if( bUp ) {
p = pIndex + wPitch * (wGridWdith - 1) + 2; for( i=0; i<wGridWdith / 2; i++) {
(*p) += wPower; p += 4; } } if( bRight ) {
for( i=0; i<wGridWdith / 2; i++) {
p = pIndex + wPitch * 2 * i + wPitch - 3; p[0] += wWidth * wPower; p[1] += wWidth * wPower; p[2] += wWidth * wPower; p[4] += wWidth * wPower; } } if( bLeft ) {
for( i=0; i<wGridWdith / 2; i++) {
p = pIndex + wPitch * 2 * i; p[1] = p[0]; p[wPitch * 2 - 3] -= wWidth * wPower; } } return (wGridWdith * 2 + 4) * wGridWdith - 2;
}