(Jin Qing's Column, Nov., 2022)

dtLink

dtLink defines a link between 2 polygons. It is an internal data structure.

A dtLink is owned by its source polygon.

How link is used

The links are used in findPath(), to search all the neighbor polygons, from the current best polygon.

fields of dtLink

dtLink has 2 required fields:

• neighbor: the neighbor polygon reference that is linked to.
• edge: index of the polygon edge that owns this link. It is used in getPortalPoints() and raycast().

If the link is a boundary link, which links to other tile, then it has more fields:

• side: defines on which side the link is. 8 sides. It is used in findPath() and raycast().
• bmin: defines the minimum sub-edge area.
• bmax: defines the maximum sub-edge area. bmin and bmax are used in portal finding.

How are links created

Links are not saved to navmesh file. They are created on navmesh loading in addTile().

dtNavMesh::addTile() add a tile to the navmesh. A tile is a square block of the map.

The main job of dtNavMesh::addTile() is to create links inside this tile and between this tile and other tiles. Actually a block indexed by (x, y) of constant size has many layers for multi-floor map. A dtMeshTile is actually a layer with an index of (x, y, layer).

5 steps to create all links:

1. Connect internal links

connectIntLinks() iterates all the polygons in the tile and create links for them by the help of neighbors information of the polygons.

2. Base off-mesh connections

baseOffMeshLinks() bases off-mesh connections to their starting polygons and connect connections inside the tile.

Off-mesh connection is between 2 points which are inside a tile or between 2 adjacent tiles.

For each off-mesh connection, there creates a specific polygon consisting of 2 vertices. See DT_POLYTYPE_OFFMESH_CONNECTION.

baseOffMeshLinks() creates 2 links for each off-mesh connection:

• From the off-mesh connection polygon to the source polygon
• From the source polygon to the off-mesh connection polygon

The destinaton polygon of the off-mesh connection is skipped here.

3. Connect external off-mesn links within this tile

connectExtOffMeshLinks() with the source and target tile be this tile.

connectExtOffMeshLinks() searches off-mesh connections that are from this tile to the target tile by checking the side direction of the connection.

It creates a link from off-mesh connection polygon to the target tile. For bidirectional connection, it also creates a link from the target polygon to the off-mesh connection polygon.

So for each off-mesh connection of this tile, 3 or 4 links are created by baseOffMeshLinks() and connectExtOffMeshLinks(), one on the source polygon, one on the destination polygon and 1/2 on the off-mesh connection polygon.

4. Connect with layers in current tile

For each layer other than this layer in this tile:

• Create links from this layer to other layer
• Create links from other layer to this layer
• Create links of the off-mesh connection from this layer to other layer
• Create links of the off-mesh connection from other layer to this layer

5. Connect with neighbour tiles

Check 9 neighbor tiles' layers, and create links just like previous step:

• Create links from this layer to neighnor layer
• Create links from neighnor layer to this layer
• Create links of the off-mesh connection from this layer to neighnor layer
• Create links of the off-mesh connection from neighnor layer to this layer

By now, for every off-mesh connection of all the loaded tiles, 3/4 links are created.

Reference

• https://blog.csdn.net/icebergliu1234/article/details/80322392

From: https://www.modernescpp.com/index.php/c-core-guidelines-how-to-pass-function-parameters

Parameter passing expression rules:

• F.15: Prefer simple and conventional ways of passing information
• F.16: For “in” parameters, pass cheaply-copied types by value and others by reference to const
• F.17: For “in-out” parameters, pass by reference to non-const
• F.18: For “consume” parameters, pass by X&& and std::move the parameter
• F.19: For “forward” parameters, pass by TP&& and only std::forward the parameter
• F.20: For “out” output values, prefer return values to output parameters
• F.21: To return multiple “out” values, prefer returning a tuple or struct
• F.60: Prefer T* over T& when “no argument” is a valid option

from: C++ Programming Guidelines (cginternals.github.io)

When naming accessors within classes, non-trivial getters and queries, i.e., those that perform calculations, you should prepended get. All other getters have no prefix and setters have the set prefix.

grpc++不支持异步多次写入

(金庆的专栏 2017.5)

用grpc_cb代替grpc++

(金庆的专栏 2017.1)

jinq0123/grpc_cb
是 Google gRpc 的C++库。
它依赖于 grpc, 采用回调接口，简化了使用，用来代替 grpc++ 库。

使用简介如下。

定义服务

用 proto 文件定义服务：

• route_guide.pb.h, 消息类定义
• route_guide.pb.cc, 消息类实现
• route_guide.grpc_cb.pb.h, 服务类定义
• route_guide.grpc_cb.pb.cc, 服务类实现

生成的命名空间RouteGuide将包含

• 客户端使用的Stub类.
• 需服务器实现的Service类.

客户端调用RPC

同步调用

ChannelSptr channel(new Channel("localhost:50051"));
Stub stub(channel);

Point point = MakePoint(0, 0);
Feature feature;
Status status = stub.BlockingGetFeature(point, &feature);

异步调用

stub.AsyncGetFeature(point,
	[](const Feature& feature) {
		cout << feature.name() << endl;
	});

服务器实现

先实现服务类

GetFeature()不必立即应答，可复制保存replier后直接返回， 待应答内容准备完成后，再调用Reply().

开启服务