烘培代码在 rcBuildHeightfieldLayers
本质上是为每个tile生成高度上的不同layer
算法的关键是三层循环:
for z 轴循环
for x 轴循环
for 高度span 循环
判断span和相邻span的连通性(x/z平面相邻cell)
如果联通, 则标注为同一个layer, 也就是在x/z平面上标注layer, 形成像是互不相交的面包片叠放的样子, 也有有坡度的layer
然后做了一些layer合并处理, 相邻的layer且在x/z平面不重叠且合并后高度差较小的, 可以合并为一个layer
同时layer记录了当前layer的上下高度范围, 边界(坐标系), 边界(体素),
heights记录了layer内每个span相对于layer的体素下边界的高度差(体素单位)
areas记录了layer内每个span的areas
cons记录了layer和span的相邻关系
(注意代码里改了一些变量的命名, 过于简化的变量名不利于新手看懂代码)
(另外, 代码里把y改成了z, recast本身代码里体素遍历都是 x/y平面, 按Unity习惯, 改成了 x/z 平面遍历, y代表高度)
/// See the #rcConfig documentation for more information on the configuration parameters.
///
/// @see rcAllocHeightfieldLayerSet, rcCompactHeightfield, rcHeightfieldLayerSet, rcConfig
bool rcBuildHeightfieldLayers(rcContext* ctx, rcCompactHeightfield& chf,
const int borderSize, const int walkableHeight,
rcHeightfieldLayerSet& lset)
{
rcAssert(ctx);
rcScopedTimer timer(ctx, RC_TIMER_BUILD_LAYERS);
const int w = chf.width;
const int h = chf.height;
rcScopedDelete<unsigned char> srcReg((unsigned char*)rcAlloc(sizeof(unsigned char)*chf.spanCount, RC_ALLOC_TEMP));
if (!srcReg)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'srcReg' (%d).", chf.spanCount);
return false;
}
memset(srcReg,0xff,sizeof(unsigned char)*chf.spanCount);
const int nsweeps = chf.width;
rcScopedDelete<rcLayerSweepSpan> sweeps((rcLayerSweepSpan*)rcAlloc(sizeof(rcLayerSweepSpan)*nsweeps, RC_ALLOC_TEMP));
if (!sweeps)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'sweeps' (%d).", nsweeps);
return false;
}
// Partition walkable area into monotone regions.
int prevCount[256];
unsigned char regId = 0;
//注意这里是三层循环:
// for z 平面
// for x 平面
// for y 平面 (高度)
// 最内层是对每个y平面的处理, 在每个y层面上根据span在x/z的连接性做region分配和合并, 也就是layer的意义: 按高度分层. 像是切片面包.
// 从3d视角看是, 遍历x/z平面的每个cell, 依次检查当前cell与相邻cell在高度上的切片span是否有联通的, 如果有联通就把x/z平面相邻的cell上region赋值为相同id. 让x/z平面形成region.高度上
for (int z = borderSize; z < h-borderSize; ++z)
{
// prevCount 记录的是当前x轴上的sweep和上一轮x循环(-z方向)的region相连的span数量.
memset(prevCount,0,sizeof(int)*regId);
//(按行扫描编号), 这个编号在y的循环体内, 也就是每扫描一行x则重置, 扫描完一行后后面会把sweepId变成regionId, 所以重置没问题.
unsigned char nowSweepId = 0;
for (int x = borderSize; x < w-borderSize; ++x)
{
const rcCompactCell& c = chf.cells[x+z*w];
for (int i = (int)c.index, ni = (int)(c.index+c.count); i < ni; ++i)
{
const rcCompactSpan& s = chf.spans[i];
if (chf.areas[i] == RC_NULL_AREA) continue;
unsigned char sweepId = 0xff;
//(-1, 0)方向如果有连接
// -x
if (rcGetCon(s, 0) != RC_NOT_CONNECTED)
{
const int ax = x + rcGetDirOffsetX(0);
const int ay = z + rcGetDirOffsetY(0);
const int ai = (int)chf.cells[ax+ay*w].index + rcGetCon(s, 0);
//如果连接的不是NULL_AREA且它的sweepId并不是未初始化状态(未设置, 默认值0xff) (sweepId存储在srcReg里)
//那么把自己的sweepId也设置为相邻这个span的sweepId,因为是从左到右遍历, 所以-x是刚刚遍历过的,如果连接(x轴相邻的span)且有srcReg, 则设置为相同srcReg
if (chf.areas[ai] != RC_NULL_AREA && srcReg[ai] != 0xff)
sweepId = srcReg[ai];
}
// 如果和左侧相邻span(-1, 0)没有连接, 或者连接的area是NULL, 或者sweepId无效, 则把自己的sweepId设置为新的id. (新分配一个扫描编号)
if (sweepId == 0xff)
{
sweepId = nowSweepId++;
sweeps[sweepId].nei = 0xff;
sweeps[sweepId].ns = 0;
}
// 检查完-x方向. 再检查之前扫描过的z方向的邻居 (上一轮扫描过的)
// 如果相连且sweepId不是0xff, 则判断是不是刚刚x方向新加的sweepId(还没邻居), 如果是则把z方向的这个邻居设置成自己的邻居
// 如果当前邻居是z方向的这个span, 则把ns++, 把邻居sweepId记录的数量也加1(prevCount[nrSweepId]++)
// 如果当前邻居不是z方向这个span, 说明和-z这一行有两个邻居, 则把邻居置为无效值
// (0, -1) x/z平面的下面 -> -z, 注意源码是 x/y 平面, 这里原本注释写的 -y
if (rcGetCon(s,3) != RC_NOT_CONNECTED)
{
const int ax = x + rcGetDirOffsetX(3);
const int ay = z + rcGetDirOffsetY(3);
const int ai = (int)chf.cells[ax+ay*w].index + rcGetCon(s, 3);
const unsigned char nrRegId = srcReg[ai];
if (nrRegId != 0xff)
{
// Set neighbour when first valid neighbour is encoutered.
if (sweeps[sweepId].ns == 0)
sweeps[sweepId].nei = nrRegId;
if (sweeps[sweepId].nei == nrRegId)
{
// Update existing neighbour
sweeps[sweepId].ns++;
prevCount[nrRegId]++;
}
else
{
// This is hit if there is nore than one neighbour.
// Invalidate the neighbour.
sweeps[sweepId].nei = 0xff;
}
}
}
srcReg[i] = sweepId;
}
}
// Create unique ID.
for (int i = 0; i < nowSweepId; ++i)
{
/// 如果邻居设置了, 而且邻居连接我的数量和我数量相同则说明我们是完全相临的, 可以合并, 否则意味着我的邻居可能还有其他sweepId和他相连.
/// 类似下面, A先扫描完, 形成了一个完整连续的region=1, 再遍历B时, prevCount[1] = 4, (A行3个1和1个2), 但是sweeps[1] = 3, (B行3个1)
/// 所以此时B行里的1和A行里的1不能合并了. 要给B行的1分配新的regionId
///
/// <--- -x方向(左)
/// |
/// B: [1] [1] [1] [2] | -> 此处的1, 2都还是sweepId, 代表从左到右的扫描分割序号.
/// A: [1] [1] [1] [1] [1] | -> 此时的1已经是regionId了.
/// -z方向(下)
///
///
/// B: [1] [1] |
/// A: [1] [1] [1] | -> 这种情况可以合并, prevCount[A1].nei = 2, sweeps[B1].ns = 2
///
/// B: [1] [1] [1] [1] |
/// A: [1] [1] [1] | -> 这种情况也可以合并, prevCount[A1].nei = 3, sweeps[B1].ns = 3, (B第四个[1]因为和下面无连接, 所以两边都不计数)
///
/// If the neighbour is set and there is only one continuous connection to it,
/// the sweep will be merged with the previous one, else new region is created.
if (sweeps[i].nei != 0xff && prevCount[sweeps[i].nei] == (int)sweeps[i].ns)
{
sweeps[i].id = sweeps[i].nei;
}
else
{
if (regId == 255)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Region ID overflow.");
return false;
}
sweeps[i].id = regId++;
}
}
// 之前srcReg里记录的是sweepId, 现在改回regionId
// Remap local sweep ids to region ids.
for (int x = borderSize; x < w-borderSize; ++x)
{
const rcCompactCell& c = chf.cells[x+z*w];
for (int i = (int)c.index, ni = (int)(c.index+c.count); i < ni; ++i)
{
if (srcReg[i] != 0xff)
srcReg[i] = sweeps[srcReg[i]].id;
}
}
}
// Allocate and init layer regions.
const int nregs = (int)regId;
rcScopedDelete<rcLayerRegion> regs((rcLayerRegion*)rcAlloc(sizeof(rcLayerRegion)*nregs, RC_ALLOC_TEMP));
if (!regs)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'regs' (%d).", nregs);
return false;
}
memset(regs, 0, sizeof(rcLayerRegion)*nregs);
for (int i = 0; i < nregs; ++i)
{
regs[i].layerId = 0xff;
regs[i].ymin = 0xffff;
regs[i].ymax = 0;
}
// Find region neighbours and overlapping regions.
for (int z = 0; z < h; ++z) //遍历 z
{
for (int x = 0; x < w; ++x) //遍历 x/z 平面
{
const rcCompactCell& c = chf.cells[x+z*w];
//记录y方向的区域id和数量
unsigned char lregs[RC_MAX_LAYERS];
int nlregs = 0;
for (int i = (int)c.index, ni = (int)(c.index+c.count); i < ni; ++i) //遍历 y 方向 span
{
const rcCompactSpan& s = chf.spans[i];
const unsigned char regionId = srcReg[i];
if (regionId == 0xff) continue; //跳过没有区域的span
regs[regionId].ymin = rcMin(regs[regionId].ymin, s.y);
regs[regionId].ymax = rcMax(regs[regionId].ymax, s.y);
// Collect all region layers.
if (nlregs < RC_MAX_LAYERS)
lregs[nlregs++] = regionId;
// Update neighbours
// 遍历4个方向, 记录邻居区域信息 (和自己不同区域)
for (int dir = 0; dir < 4; ++dir)
{
if (rcGetCon(s, dir) != RC_NOT_CONNECTED)
{
const int ax = x + rcGetDirOffsetX(dir);
const int ay = z + rcGetDirOffsetY(dir);
const int ai = (int)chf.cells[ax+ay*w].index + rcGetCon(s, dir);
const unsigned char nrReg = srcReg[ai];
if (nrReg != 0xff && nrReg != regionId) //邻居的region 和 自己不一样
{
// Don't check return value -- if we cannot add the neighbor
// it will just cause a few more regions to be created, which
// is fine.
addUnique(regs[regionId].neis, regs[regionId].nneis, RC_MAX_NEIS, nrReg);
}
}
}
}
// 两层遍历高度(y)方向的区域 (两两检查),
// Update overlapping regions.
for (int i = 0; i < nlregs-1; ++i)
{
for (int j = i+1; j < nlregs; ++j)
{
if (lregs[i] != lregs[j])
{
rcLayerRegion& ri = regs[lregs[i]];
rcLayerRegion& rj = regs[lregs[j]];
//在两个region的layers里记录该region在x/z平面上重叠的其他高度的regionId. 用于索引高度上的不同层.
if (!addUnique(ri.layers, ri.nlayers, RC_MAX_LAYERS, lregs[j]) ||
!addUnique(rj.layers, rj.nlayers, RC_MAX_LAYERS, lregs[i]))
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: layer overflow (too many overlapping walkable platforms). Try increasing RC_MAX_LAYERS.");
return false;
}
}
}
}
}
}
// Create 2D layers from regions.
unsigned char layerId = 0;
static const int MAX_STACK = 64;
unsigned char stack[MAX_STACK];
int nstack = 0;
for (int i = 0; i < nregs; ++i)
{
rcLayerRegion& root = regs[i];
// Skip already visited.
if (root.layerId != 0xff)
continue;
// Start search.
// 分配 layerId
root.layerId = layerId;
root.base = 1;
nstack = 0;
stack[nstack++] = (unsigned char)i; //region序号入栈
while (nstack)
{
// Pop front
rcLayerRegion& reg = regs[stack[0]];
nstack--;
for (int j = 0; j < nstack; ++j) //移除stack第一个元素.
stack[j] = stack[j+1];
const int nneis = (int)reg.nneis;
for (int j = 0; j < nneis; ++j)
{
const unsigned char nei = reg.neis[j];
rcLayerRegion& nrReg = regs[nei];
// Skip already visited.
if (nrReg.layerId != 0xff)
continue;
// Skip if the neighbour is overlapping root region.
// 跳过 邻居是x/z重叠的不同高度的region
if (contains(root.layers, root.nlayers, nei))
continue;
// Skip if the height range would become too large.
// 如果两个区域加起来的高度落差太大 跳过 (因为高度差不大的情况下会合并layer, 但是合并太多后会导致layer上下表面的高差越来越大, 这时候就要打断合并了)
const int ymin = rcMin(root.ymin, nrReg.ymin);
const int ymax = rcMax(root.ymax, nrReg.ymax);
if ((ymax - ymin) >= 255)
continue;
if (nstack < MAX_STACK)
{
// Deepen 邻居入栈
stack[nstack++] = (unsigned char)nei;
// Mark layer id
// 将邻居的layerId设置为自己的layerId. 合并成一个layer
nrReg.layerId = layerId;
// Merge current layers to root.
// 将邻居的高度layers也合并到自己的layers, (合并成一个layer了, 高度重叠区域信息也要合并).
for (int k = 0; k < nrReg.nlayers; ++k)
{
if (!addUnique(root.layers, root.nlayers, RC_MAX_LAYERS, nrReg.layers[k]))
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: layer overflow (too many overlapping walkable platforms). Try increasing RC_MAX_LAYERS.");
return false;
}
}
root.ymin = rcMin(root.ymin, nrReg.ymin); // 更新合并后的layer上下表面.
root.ymax = rcMax(root.ymax, nrReg.ymax);
}
}
}
layerId++;
}
// Merge non-overlapping regions that are close in height.
// 合并高度上差异不大, 而且没有重叠的区域, 楼梯, 坡等
const unsigned short mergeHeight = (unsigned short)walkableHeight * 4;
for (int i = 0; i < nregs; ++i)
{
rcLayerRegion& ri = regs[i];
if (!ri.base) continue; //只需要查询layer的 base region
unsigned char newId = ri.layerId;
for (;;)
{
unsigned char oldId = 0xff;
for (int j = 0; j < nregs; ++j) //双层遍历 region 两两计算
{
if (i == j) continue;
rcLayerRegion& rj = regs[j];
if (!rj.base) continue;
// Skip if the regions are not close to each other.
// 两个区域的上下表面+合并高差 不重叠, 则无法合并
if (!overlapRange(ri.ymin,ri.ymax+mergeHeight, rj.ymin,rj.ymax+mergeHeight))
continue;
// Skip if the height range would become too large.
const int ymin = rcMin(ri.ymin, rj.ymin);
const int ymax = rcMax(ri.ymax, rj.ymax);
if ((ymax - ymin) >= 255) //合并后高差太大 跳过
continue;
// Make sure that there is no overlap when merging 'ri' and 'rj'.
bool overlap = false;
// Iterate over all regions which have the same layerId as 'rj'
for (int k = 0; k < nregs; ++k)
{
if (regs[k].layerId != rj.layerId)
continue;
// Check if region 'k' is overlapping region 'ri'
// Index to 'regs' is the same as region id.
// 和j相同layerId的区域, 判断是否和ri有重叠, 如果有重叠说明合并regionI 和 regionJ 后会导致用一个region在x/z平面出现重叠. 所以此时要break. 不能合并
if (contains(ri.layers,ri.nlayers, (unsigned char)k))
{
overlap = true;
break;
}
}
// Cannot merge of regions overlap.
if (overlap)
continue;
// Can merge i and j.
oldId = rj.layerId;
break;
}
// Could not find anything to merge with, stop.
if (oldId == 0xff)
break;
// Merge
for (int j = 0; j < nregs; ++j)
{
rcLayerRegion& rj = regs[j];
if (rj.layerId == oldId)
{
rj.base = 0;
// Remap layerIds.
rj.layerId = newId;
// Add overlaid layers from 'rj' to 'ri'.
// 合并之后, 同样也需要 将邻居的高度layers也合并到自己的layers, (合并成一个layer了, 高度重叠区域信息也要合并).
for (int k = 0; k < rj.nlayers; ++k)
{
if (!addUnique(ri.layers, ri.nlayers, RC_MAX_LAYERS, rj.layers[k]))
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: layer overflow (too many overlapping walkable platforms). Try increasing RC_MAX_LAYERS.");
return false;
}
}
// Update height bounds.
ri.ymin = rcMin(ri.ymin, rj.ymin); // 更新合并后的layer上下表面.
ri.ymax = rcMax(ri.ymax, rj.ymax);
}
}
}
}
// 合并后layerId不连续了, 所以这里要重新remap下, 保持layerId连续
// Compact layerIds
unsigned char remap[256];
memset(remap, 0, 256);
// Find number of unique layers.
layerId = 0;
for (int i = 0; i < nregs; ++i)
remap[regs[i].layerId] = 1;
for (int oldLayerId = 0; oldLayerId < 256; ++oldLayerId)
{
if (remap[oldLayerId])
remap[oldLayerId] = layerId++;
else
remap[oldLayerId] = 0xff;
}
// Remap ids.
for (int i = 0; i < nregs; ++i)
regs[i].layerId = remap[regs[i].layerId]; //从remap里查询oldLayerId对应的新layerId, 并赋值
// No layers, return empty.
if (layerId == 0)
return true;
// Create layers.
rcAssert(lset.layers == 0);
const int lw = w - borderSize*2;
const int lh = h - borderSize*2;
// Build contracted bbox for layers.
float bmin[3], bmax[3];
rcVcopy(bmin, chf.bmin);
rcVcopy(bmax, chf.bmax);
bmin[0] += borderSize*chf.cs;
bmin[2] += borderSize*chf.cs;
bmax[0] -= borderSize*chf.cs;
bmax[2] -= borderSize*chf.cs;
lset.nlayers = (int)layerId;
lset.layers = (rcHeightfieldLayer*)rcAlloc(sizeof(rcHeightfieldLayer)*lset.nlayers, RC_ALLOC_PERM);
if (!lset.layers)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'layers' (%d).", lset.nlayers);
return false;
}
memset(lset.layers, 0, sizeof(rcHeightfieldLayer)*lset.nlayers);
// Store layers.
for (int i = 0; i < lset.nlayers; ++i)
{
unsigned char curId = (unsigned char)i;
rcHeightfieldLayer* layer = &lset.layers[curId];
const int gridSize = sizeof(unsigned char)*lw*lh; //体素x/z空间size, 二维数组长度
layer->heights = (unsigned char*)rcAlloc(gridSize, RC_ALLOC_PERM);
if (!layer->heights)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'heights' (%d).", gridSize);
return false;
}
memset(layer->heights, 0xff, gridSize);
layer->areas = (unsigned char*)rcAlloc(gridSize, RC_ALLOC_PERM);
if (!layer->areas)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'areas' (%d).", gridSize);
return false;
}
memset(layer->areas, 0, gridSize);
layer->cons = (unsigned char*)rcAlloc(gridSize, RC_ALLOC_PERM);
if (!layer->cons)
{
ctx->log(RC_LOG_ERROR, "rcBuildHeightfieldLayers: Out of memory 'cons' (%d).", gridSize);
return false;
}
memset(layer->cons, 0, gridSize);
// Find layer height bounds.
int hmin = 0, hmax = 0; //上下表面高度 (体素单位)
for (int j = 0; j < nregs; ++j)
{
if (regs[j].base && regs[j].layerId == curId)
{
hmin = (int)regs[j].ymin;
hmax = (int)regs[j].ymax; //此处应该可以break ?
}
}
layer->width = lw;
layer->height = lh;
layer->cs = chf.cs;
layer->ch = chf.ch;
// Adjust the bbox to fit the heightfield.
rcVcopy(layer->bmin, bmin);
rcVcopy(layer->bmax, bmax);
layer->bmin[1] = bmin[1] + hmin*chf.ch; //体素高度转坐标高度
layer->bmax[1] = bmin[1] + hmax*chf.ch;
layer->hmin = hmin;
layer->hmax = hmax;
// Update usable data region.
layer->minx = layer->width;
layer->maxx = 0;
layer->miny = layer->height;
layer->maxy = 0;
// Copy height and area from compact heightfield.
for (int z = 0; z < lh; ++z)
{
for (int x = 0; x < lw; ++x)
{
const int cx = borderSize+x;
const int cz = borderSize+z;
const rcCompactCell& c = chf.cells[cx+cz*w];
for (int j = (int)c.index, nj = (int)(c.index+c.count); j < nj; ++j)
{
const rcCompactSpan& span = chf.spans[j];
// Skip unassigned regions.
if (srcReg[j] == 0xff)
continue;
// Skip of does nto belong to current layer.
unsigned char lid = regs[srcReg[j]].layerId;
if (lid != curId)
continue;
// Update data bounds.
layer->minx = rcMin(layer->minx, x);
layer->maxx = rcMax(layer->maxx, x);
layer->miny = rcMin(layer->miny, z);
layer->maxy = rcMax(layer->maxy, z);
// Store height and area type.
const int idx = x+z*lw;
layer->heights[idx] = (unsigned char)(span.y - hmin);
layer->areas[idx] = chf.areas[j];
// Check connection.
unsigned char portal = 0;
unsigned char con = 0;
for (int dir = 0; dir < 4; ++dir)
{
if (rcGetCon(span, dir) != RC_NOT_CONNECTED)
{
const int ax = cx + rcGetDirOffsetX(dir);
const int ay = cz + rcGetDirOffsetY(dir);
const int ai = (int)chf.cells[ax+ay*w].index + rcGetCon(span, dir);
unsigned char alid = srcReg[ai] != 0xff ? regs[srcReg[ai]].layerId : 0xff;
// Portal mask
if (chf.areas[ai] != RC_NULL_AREA && lid != alid)
{
portal |= (unsigned char)(1<<dir);
// Update height so that it matches on both sides of the portal.
const rcCompactSpan& as = chf.spans[ai];
if (as.y > hmin)
layer->heights[idx] = rcMax(layer->heights[idx], (unsigned char)(as.y - hmin));
}
// Valid connection mask
// 相邻的同layer的span连接信息记录在 cons的低4位. (上下左右)
if (chf.areas[ai] != RC_NULL_AREA && lid == alid)
{
const int nx = ax - borderSize;
const int ny = ay - borderSize;
if (nx >= 0 && ny >= 0 && nx < lw && ny < lh)
con |= (unsigned char)(1<<dir);
}
}
}
layer->cons[idx] = (portal << 4) | con; //相邻的不同layer的信息记录在cons的高4位.
}
}
}
if (layer->minx > layer->maxx)
layer->minx = layer->maxx = 0;
if (layer->miny > layer->maxy)
layer->miny = layer->maxy = 0;
}
return true;
}有两个文档也可以看一下, 看懂了上面的代码再去看文章就清楚多了. 如果不好理解代码. 可以结合文章图例一起看. 代码注释已经非常详细了, 只是没有图例
https://blog.csdn.net/zstu_zy/article/details/97247013
https ://www.jianshu.com/p/f6cd9b7696f6