游戏小地图方案

Unity小地图的实现

游戏，特别是RPG类型，基本都需要添加小地图功能来辅助玩家。

实现小地图需解决的问题：

1. 小地图（贴图）从哪里来？
2. 如何把场景中单位的坐标转换到小地图上
3. 小地图视角怎么跟玩家视角一致

思路：

1. 让美术垂直90°方向以正交视角俯视整个场景，然后截取场景输出成图片，截取的大小让美术设置，一般不超过2048*2048
2. 保存截图时的矩阵
3. 通过第2点保存的矩阵，在游戏运行时把场景中单位的世界坐标转换到小地图下的局部坐标

实现：

1. 根据设置（这里写死了800*600），设定截图窗口的大小，同时Camera视角校准为玩家视角，我这里是直接使用Scene窗口

if (GUILayout.Button("调整截图窗口大小"))
{   
    var windowSize = Vector2(800,600);
    var lastSceneView = SceneView.lastActiveSceneView;

    // 场景的Main Camera
    var mainCamera = UnityEngine.Camera.main;
    // SmoothFollow是镜头跟踪的组件，这里知道SmoothFollow里有个rotationAngle字段是记录玩家视角即可
    XS.SmoothFollow smoothFollow = null;

    if (mainCamera)
    {
        smoothFollow = mainCamera.GetComponent<XS.SmoothFollow>();
    }
    if (smoothFollow == null)
    {
        return;
    }

    lastSceneView.position = new Rect(Vector3.zero, windowSize);

    Quaternion currentRotation = Quaternion.Euler(90, smoothFollow.rotationAngle, 0);
    lastSceneView.LookAt(Vector3.zero, currentRotation, lastSceneView.size, true);
    lastSceneView.isRotationLocked = true;
}

2. 截图时，以Scene的大小为图片宽高，并预先算出此时的world2Screen矩阵和screen2World矩阵，用于后面的逻辑运算

if (GUILayout.Button("截取小地图"))
{
    var lastSceneView = SceneView.lastActiveSceneView;
    var sceneCamera = lastSceneView.camera;
    if (!sceneCamera.orthographic)
    {
        return;
    }

    var width = sceneCamera.pixelWidth;
    var height = sceneCamera.pixelHeight;
    var cameraPos = sceneCamera.transform.position;
    var camreaSize = sceneCamera.orthographicSize;
    
    Matrix4x4 world2Screen = sceneCamera.projectionMatrix * sceneCamera.worldToCameraMatrix;
    Matrix4x4 screen2World = world2Screen.inverse;

    RenderTexture sceneCameraRT = RenderTexture.GetTemporary((int)width, (int)height, 32, RenderTextureFormat.ARGBFloat);
    sceneCamera.targetTexture = sceneCameraRT;
    sceneCamera.Render();
    sceneCamera.targetTexture = null;

    // targetData是用于保存数据组件，挂载在场景的一个空Object上
    string sceneName = targetData.gameObject.scene.name;

    var path = EditorUtility.SaveFilePanel("Save SmallMap", "", sceneName, "png");
    if (!string.IsNullOrEmpty(path))
    {
        if (SaveRenderTextureToPNG(sceneCameraRT, path))
        {
            targetData.smallMapCameraCenter = cameraPos;
            targetData.smallMapCameraSize = camreaSize;

            targetData.smallMapWorldToScreenMatrix = world2Screen;
            targetData.smallMapScreenToWorldMatrix = screen2World;
            targetData.smallMapCutSize = new Vector2(width, height);

            UnityEditor.EditorUtility.SetDirty(targetData);
            UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(targetData.gameObject.scene);
        }
        else
        {
            Debug.LogError("Save RenderTexture to file error");
        }
    }
    RenderTexture.ReleaseTemporary(sceneCameraRT);
}

3. 根据第2点保存的两个矩阵和图片大小，通过以下接口(Lua实现)即可完成坐标转换，里面涉及的数学知识请自行查阅。

-- 世界坐标转图片的局部坐标
function manualWorldToScreenPoint(world2Screen, x, z, pixelWidth, pixelHeight)
    local temp = world2Screen * UnityEngine.Vector4(x, 10, z, 1.0)
    if temp.w == 0 then
        return UnityEngine.Vector3.zero
    else
        temp.x = (temp.x/temp.w + 1)*0.5 * pixelWidth
        temp.y = (temp.y/temp.w + 1)*0.5 * pixelHeight
        return temp.x, temp.y
    end
end

-- 图片的局部坐标转世界坐标
function manualScreenPointToWorld(screen2World, x, y, pixelWidth, pixelHeight)
    local in_x = 2.0 * (x / pixelWidth) - 1.0
    local in_y = 2.0 * (y / pixelHeight) - 1.0
    local in_z = 10
    local in_w = 1.0
    local pos = screen2World * UnityEngine.Vector4(in_x,in_y,in_z,in_w)
    if pos.w == 0 then
        return UnityEngine.Vector3.zero
    else
        pos.w = 1.0 / pos.w
        pos.x = pos.x*pos.w
        pos.y = pos.y*pos.w
        pos.z = pos.z*pos.w
        return pos.x, pos.z
    end
end

额外：

小地图一般需要添加小地图寻路功能，这里我使用的方案是给小地图添加PointerClick事件，根据点击的坐标点转换成世界坐标点，然后从在一点(当然是上移到场景上空)通过射线往下检测，得到与路面（路面需要设置特定Layer）的交点，这个交点就是目标点，接下来就是UnityEngine.AI.NavMeshAgent的事情了。