/// <summary>
/// Creates an height map using the Fault Formation algorithm.
/// Produces smooth terrain by adding a random line to a blank height field, and add random height to one of the two sides.
/// </summary>
/// <param name="size">Size of square HeightData to be created</param>
/// <param name="numberIteration">The number of iteration of the algorithm. More iteration yields more spaces</param>
/// <param name="minHeight">Min value of height produced from the algorithm</param>
/// <param name="maxHeight">Max value of height produced from the algorithm</param>
/// <param name="scaleHeight"></param>
/// <param name="filter"></param>
/// <returns>HeightData created with Fault Formation algorithm that has "size" of size</returns>
public static HeightMap GenerateFaultFormation(int size, int numberIteration, float minHeight, float maxHeight, float scaleHeight, float filter)
{
var heightMap = new HeightMap(size, scaleHeight);
var random = new Random();
for (var i = 0; i < numberIteration; ++i)
{
// Calculate height for this iteration
var height = maxHeight - (maxHeight - minHeight) * i / numberIteration;
var currentPassHeight = height * ((float)random.NextDouble() - 0.1f);
// Find the line mark a half space for this iteration
var point1 = new Point(random.Next(size), random.Next(size));
var point2 = new Point(random.Next(size), random.Next(size));
var halfSpaceLineVector = new Vector2(point2.X - point1.X, point2.Y - point1.Y);
for (var iX = 0; iX < size; ++iX)
{
for (var iZ = 0; iZ < size; ++iZ)
{
var currentPointLine = new Vector2(iX - point1.X, iZ - point1.Y);
float sign;
Vector2.Dot(ref halfSpaceLineVector, ref currentPointLine, out sign);
if (sign > 0) heightMap[iX, iZ] += currentPassHeight;
}
}
heightMap.FilterHeightField(filter);
}
heightMap.NormalizeHeightMap();
heightMap.CalculateMedian();
return heightMap;
}
private static void NormalizeHeightMap(HeightMap heightMap)
{
var maxHeight = float.MinValue;
var minHeight = float.MaxValue;
for (var i = 0; i < heightMap.DataSize; ++i)
{
if (maxHeight < heightMap[i]) maxHeight = heightMap[i];
if (minHeight > heightMap[i]) minHeight = heightMap[i];
}
maxHeight -= minHeight;
for (var i = 0; i < heightMap.DataSize; ++i)
heightMap[i] = (heightMap[i] - minHeight) / maxHeight;
}
private static void FilterHeightField(HeightMap data, float filter)
{
var size = data.Size;
// Erode left to right
for (var i = 0; i < size; i++)
FilterHeightBand(data, size * i, 1, size, filter);
//erode right to left
for (var i = 0; i < size; i++)
FilterHeightBand(data, size * i + size - 1, -1, size, filter);
//erode top to bottom
for (var i = 0; i < data.Size; i++)
FilterHeightBand(data, i, size, size, filter);
//erode from bottom to top
for (var i = 0; i < data.Size; i++)
FilterHeightBand(data, size * (size - 1) + i, -size, size, filter);
}
/// <summary>
/// Filters HeightData using band-based filter. by "Jason Shankel"
/// It simulates terrain erosion.
/// Throws an ArgumentOutOfRangeException if heightData is empty.
/// </summary>
/// <param name="heightData">In: Already created HeightData, Out: Smoothed HeightData</param>
/// <param name="startIndex"></param>
/// <param name="stride"></param>
/// <param name="count"></param>
/// <param name="filter"></param>
public static void FilterHeightBand(HeightMap heightData, int startIndex, int stride, int count, float filter)
{
var v = heightData[startIndex];
var j = stride;
//go through the height band and apply the erosion filter
for (var i = 0; i < count - 1; ++i)
{
heightData[startIndex + j] = filter * v + (1 - filter) * heightData[startIndex + j];
v = heightData[startIndex + j];
j += stride;
}
}
/// <summary>
/// Gets a normal vector for a given x, z coordinate and the corresponding heightmap
/// </summary>
/// <param name="heightMap"></param>
/// <param name="x"></param>
/// <param name="z"></param>
/// <returns></returns>
private static Vector4 GetNormalVector(HeightMap heightMap, int x, int z)
{
var currentP = new Vector3(x, heightMap.GetHeight(x, z), z);
Vector3 p1;
Vector3 p2;
if (x == heightMap.Size - 1 && z == heightMap.Size - 1) // Bottom right pixel
{
p1 = new Vector3(x, heightMap.GetHeight(x, z - 1), z - 1);
p2 = new Vector3(x - 1, heightMap.GetHeight(x - 1, z), z);
}
else if (x == heightMap.Size - 1) // Right border
{
p1 = new Vector3(x - 1, heightMap.GetHeight(x - 1, z), z);
p2 = new Vector3(x, heightMap.GetHeight(x, z + 1), z + 1);
}
else if (z == heightMap.Size - 1) // Bottom border
{
p1 = new Vector3(x + 1, heightMap.GetHeight(x + 1, z), z);
p2 = new Vector3(x, heightMap.GetHeight(x, z - 1), z - 1);
}
else // The rest of pixels
{
p1 = new Vector3(x, heightMap.GetHeight(x, z + 1), z + 1);
p2 = new Vector3(x + 1, heightMap.GetHeight(x + 1, z), z);
}
return new Vector4(Vector3.Normalize(Vector3.Cross(p1 - currentP, p2 - currentP)), 1);
}
/// <summary>
/// Initializes Vertex buffer data by a given height map
/// </summary>
/// <param name="heightMap"></param>
/// <param name="vertexBuffer"></param>
private static unsafe void SetVertexDataFromHeightMap(HeightMap heightMap, IntPtr vertexBuffer)
{
var vb = (VertexNormalTexture*)vertexBuffer;
var halfSize = heightMap.Size * 0.5f;
for (var iZ = 0; iZ < heightMap.Size; ++iZ)
for (var iX = 0; iX < heightMap.Size; ++iX)
{
vb[iZ * heightMap.Size + iX] = new VertexNormalTexture
{
Position = new Vector4(iX - halfSize, heightMap.GetHeight(iX, iZ), -iZ + halfSize, 1),
Normal = GetNormalVector(heightMap, iX, iZ),
TextureCoordinate = new Vector2((float)iX / heightMap.Size, (float)iZ / heightMap.Size)
};
}
}
/// <summary>
/// Initializes Vertex and Index buffers with a given height map
/// </summary>
/// <param name="heightMap"></param>
private void InitializeBuffersFromTerrain(HeightMap heightMap)
{
var commandList = Game.GraphicsContext.CommandList;
// Set data in VertexBuffer
var mappedSubResource = commandList.MapSubresource(terrainVertexBuffer, 0, MapMode.WriteDiscard);
SetVertexDataFromHeightMap(heightMap, mappedSubResource.DataBox.DataPointer);
commandList.UnmapSubresource(mappedSubResource);
// Set data in IndexBuffer
mappedSubResource = commandList.MapSubresource(terrainIndexBuffer, 0, MapMode.WriteDiscard);
var elementCount = SetIndexDataForTerrain(heightMap.Size, mappedSubResource.DataBox.DataPointer);
commandList.UnmapSubresource(mappedSubResource);
terrainMesh.Draw.DrawCount = elementCount;
}
