4

我正在使用 XNA 4.0 框架在 Visual Studio 2010 中编写游戏。我有一个从高度图生成的 3D 地形模型。我想要完成的是在某个点周围的给定半径内为这个模型着色，最终目标是向玩家显示一个单位可以在给定转弯中移动的半径。我现在用来绘制模型的方法是这样的：

void DrawModel(Model model, Matrix worldMatrix)
    {
        Matrix[] boneTransforms = new Matrix[model.Bones.Count];
        model.CopyAbsoluteBoneTransformsTo(boneTransforms);

        foreach (ModelMesh mesh in model.Meshes)
        {
            foreach (BasicEffect effect in mesh.Effects)
            {
                effect.World = boneTransforms[mesh.ParentBone.Index] * worldMatrix;
                effect.View = camera.viewMatrix;
                effect.Projection = camera.projectionMatrix;


                effect.EnableDefaultLighting();
                effect.EmissiveColor = Color.Green.ToVector3();
                effect.PreferPerPixelLighting = true;

                // Set the fog to match the black background color
                effect.FogEnabled = true;
                effect.FogColor = Color.CornflowerBlue.ToVector3();
                effect.FogStart = 1000;
                effect.FogEnd = 3200;
            }

            mesh.Draw();
        }
    }

此外，如果它是相关的，我按照本教程http://create.msdn.com/en-US/education/catalog/sample/collision_3d_heightmap创建我的高度图和地形。

提前感谢您的帮助！

4

2 回答 2

3

您可以使用着色器来实现...

您只需将中心的世界位置和半径作为参数传递，并让像素着色器接收从顶点着色器插值的像素世界位置作为纹理坐标...然后只需检查像素的距离如果像素位置在范围内，则将其定位到中心并用颜色着色...

于 2012-08-08T23:38:36.347 回答
0

您正在寻找的技术称为贴花。

您必须提取要绘制圆圈的地形部分，将适当的纹理应用到该部分并将其与地形混合绘制。

对于基于统一网格的地形，如下所示：

你有贴花的中心位置和它的半径。然后您可以确定网格中的最小和最大行/列，以便单元格包括每个绘制的区域。从这些顶点创建一个新的顶点缓冲区。可以从高度图中读取位置。您必须更改纹理坐标，以便将纹理放置在正确的位置。假设中心位置有坐标(0.5, 0.5)，中心位置+（半径，半径）有坐标(1, 1)等等。有了它，您应该能够找到每个顶点的纹理坐标的方程。

提取的网格

在上面的例子中，左上角的红色顶点的纹理坐标约为(-0.12, -0.05)

然后你有地形的子网格。将贴花纹理应用到它。设置适当的深度偏差（您必须尝试一些值）。在大多数情况下，负的 SlopeScaleDepthBias 会起作用。关闭采样器中的纹理坐标环绕。绘制子网格。

这是我为此目的编写的一些 VB SlimDX 代码：

Public Sub Init()
    Verts = (Math.Ceiling(2 * Radius / TriAngleWidth) + 2) ^ 2
    Tris = (Math.Ceiling(2 * Radius / TriAngleWidth) + 1) ^ 2 * 2

    Dim Indices(Tris * 3 - 1) As Integer
    Dim curN As Integer
    Dim w As Integer
    w = (Math.Ceiling(2 * Radius / TriAngleWidth) + 2)
    For y As Integer = 0 To w - 2
        For x As Integer = 0 To w - 2
            Indices(curN) = x + y * w : curN += 1
            Indices(curN) = x + (y + 1) * w : curN += 1
            Indices(curN) = (x + 1) + (y) * w : curN += 1
            Indices(curN) = x + (y + 1) * w : curN += 1
            Indices(curN) = (x + 1) + (y + 1) * w : curN += 1
            Indices(curN) = (x + 1) + y * w : curN += 1
        Next
    Next

    VB = New Buffer(D3DDevice, New BufferDescription(Verts * VertexPosTexColor.Struct.SizeOfBytes, ResourceUsage.Dynamic, BindFlags.VertexBuffer, CpuAccessFlags.Write, ResourceOptionFlags.None, VertexPosTexColor.Struct.SizeOfBytes))
    IB = New Buffer(D3DDevice, New DataStream(Indices, False, False), New BufferDescription(4 * Tris * 3, ResourceUsage.Default, BindFlags.IndexBuffer, CpuAccessFlags.None, ResourceOptionFlags.None, 4))
End Sub

Public Sub Update()
    Dim Vertex(Verts - 1) As VertexPosTexColor.Struct
    Dim curN As Integer
    Dim rad As Single 'The decal radius
    Dim height As Single
    Dim p As Vector2
    Dim yx, yz As Integer
    Dim t As Vector2 'texture coordinates
    Dim center As Vector2 'decal center
    For y As Integer = Math.Floor((center.Y - rad) / TriAngleWidth) To Math.Floor((center.Y - rad) / TriAngleWidth) + Math.Ceiling(2 * rad / TriAngleWidth) + 1
        For x As Integer = Math.Floor((center.X - rad) / TriAngleWidth) To Math.Floor((center.X - rad) / TriAngleWidth) + Math.Ceiling(2 * rad / TriAngleWidth) + 1
            p.X = x * TriAngleWidth
            p.Y = y * TriAngleWidth

            yx = x : yz = y
            If yx < 0 Then yx = 0
            If yx > HeightMap.GetUpperBound(0) Then yx = HeightMap.GetUpperBound(0)
            If yz < 0 Then yz = 0
            If yz > HeightMap.GetUpperBound(1) Then yz = HeightMap.GetUpperBound(1)
            height = HeightMap(yx, yz)
            t.X = (p.X - center.X) / (2 * rad)  + 0.5
            t.Y = (p.Y - center.Y) / (2 * rad) + 0.5
            Vertex(curN) = New VertexPosTexColor.Struct With {.Position = New Vector3(p.X, hoehe, p.Y), .TexCoord = t, .Color = New Color4(1, 1, 1, 1)} : curN += 1
        Next
    Next
    Dim data = D3DContext.MapSubresource(VB, MapMode.WriteDiscard, MapFlags.None)
    data.Data.WriteRange(Vertex)
    D3DContext.UnmapSubresource(VB, 0)
End Sub

这是相应的 C# 代码。

public void Init()
{
    Verts = Math.Pow(Math.Ceiling(2 * Radius / TriAngleWidth) + 2, 2);
    Tris = Math.Pow(Math.Ceiling(2 * Radius / TriAngleWidth) + 1, 2) * 2;

    int[] Indices = new int[Tris * 3];
    int curN;
    int w;
    w = (Math.Ceiling(2 * Radius / TriAngleWidth) + 2);
    for(int y = 0; y <= w - 2; ++y)
    {
        for(int x = 0; x <= w - 2; ++x)
        {
            Indices[curN] = x + y * w ; curN += 1;
            Indices[curN] = x + (y + 1) * w ; curN += 1;
            Indices[curN] = (x + 1) + (y) * w ; curN += 1;
            Indices[curN] = x + (y + 1) * w ; curN += 1;
            Indices[curN] = (x + 1) + (y + 1) * w ; curN += 1;
            Indices[curN] = (x + 1) + y * w ; curN += 1;
        }
    }

    VB = new Buffer(D3DDevice, new BufferDescription(Verts * VertexPosTexColor.Struct.SizeOfBytes, ResourceUsage.Dynamic, BindFlags.VertexBuffer, CpuAccessFlags.Write, ResourceOptionFlags.None, VertexPosTexColor.Struct.SizeOfBytes));
    IB = new Buffer(D3DDevice, new DataStream(Indices, False, False), new BufferDescription(4 * Tris * 3, ResourceUsage.Default, BindFlags.IndexBuffer, CpuAccessFlags.None, ResourceOptionFlags.None, 4));
}

public void Update()
{
    VertexPosTexColor.Struct[] Vertex = new VertexPosTexColor.Struct[Verts] ;
    int curN;
    float rad; //The decal radius
    float height;
    Vector2 p;
    int yx, yz;
    Vector2 t; //texture coordinates
    Vector2 center; //decal center
    for(int y = Math.Floor((center.Y - rad) / TriAngleWidth); y <= Math.Floor((center.Y - rad) / TriAngleWidth) + Math.Ceiling(2 * rad / TriAngleWidth) + 1; ++y)
        for(int x = Math.Floor((center.X - rad) / TriAngleWidth); x <= Math.Floor((center.X - rad) / TriAngleWidth) + Math.Ceiling(2 * rad / TriAngleWidth) + 1; ++x)
        {
            p.X = x * TriAngleWidth;
            p.Y = y * TriAngleWidth;

            yx = x ; yz = y;
            if( yx < 0)
                yx = 0;
            if (yx > HeightMap.GetUpperBound(0))
                yx = HeightMap.GetUpperBound(0);
            if (yz < 0)
                yz = 0;
            if (yz > HeightMap.GetUpperBound(1))
                yz = HeightMap.GetUpperBound(1);
            height = HeightMap[yx, yz];
            t.X = (p.X - center.X) / (2 * rad)  + 0.5;
            t.Y = (p.Y - center.Y) / (2 * rad) + 0.5;
            Vertex[curN] = new VertexPosTexColor.Struct() {Position = new Vector3(p.X, hoehe, p.Y), TexCoord = t, Color = New Color4(1, 1, 1, 1)}; curN += 1;
        }
    }
    var data = D3DContext.MapSubresource(VB, MapMode.WriteDiscard, MapFlags.None);
    data.Data.WriteRange(Vertex);
    D3DContext.UnmapSubresource(VB, 0);
}
于 2012-08-04T21:17:03.170 回答