在3D图形编程中，有时希望在场景中添加一些静态文本，以提高可读性。例如，在游戏开发中，可能需要在屏幕上显示得分、状态信息或提示。本文将介绍如何在3D场景中创建一个基于文本的标签。
创建文本标签的过程可以分为以下几个步骤：
这个过程可能会涉及到一些关键的技术点，比如如何根据文本内容确定位图的大小，以及如何使用ManualObject。
以下是使用C#语言实现上述功能的代码示例：
private static ManualObject createALabel(SceneManager Smgr, String text)
{
String textureName = Guid.NewGuid().ToString();
System.Drawing.Font font = new System.Drawing.Font("Calibri", 12, FontStyle.Bold);
Bitmap bitmap = new Bitmap(1, 1);
Graphics g = Graphics.FromImage(bitmap);
float measureString = g.MeasureString(text, font).Width;
bitmap = new Bitmap((int)measureString, (int)g.MeasureString(text, font).Height);
g = Graphics.FromImage(bitmap);
g.FillRectangle(Brushes.Black, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height));
g.DrawString(text, font, new System.Drawing.SolidBrush(Color.White), new Point(3, 3));
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
Stream oStream = new MemoryStream();
g.Save();
bitmap.Save(oStream, ImageFormat.Png);
oStream.Flush();
bitmap.Dispose();
oStream.Position = 0;
BinaryReader oBinaryReader = new BinaryReader(oStream);
byte[] pBuffer = oBinaryReader.ReadBytes((int)oBinaryReader.BaseStream.Length);
oStream.Close();
GCHandle handle = GCHandle.Alloc(pBuffer, GCHandleType.Pinned);
byte* pUnsafeByte = (byte*)handle.AddrOfPinnedObject();
void* pUnsafeBuffer = (void*)handle.AddrOfPinnedObject();
MemoryDataStream oMemoryStream = new MemoryDataStream(pUnsafeBuffer, (uint)pBuffer.Length);
DataStreamPtr oPtrDataStream = new DataStreamPtr(oMemoryStream);
Mogre.Image oMogreImage = new Mogre.Image().Load(oPtrDataStream, "png");
TextureManager.Singleton.LoadImageW(textureName, ResourceGroupManager.DEFAULT_RESOURCE_GROUP_NAME, oMogreImage);
handle.Free();
String matNam = Guid.NewGuid().ToString();
MaterialPtr _dynamicMaterial = MaterialManager.Singleton.Create(matNam, ResourceGroupManager.DEFAULT_RESOURCE_GROUP_NAME);
Pass pass = _dynamicMaterial.GetTechnique(0).GetPass(0);
pass.ShadingMode = ShadeOptions.SO_PHONG;
TextureUnitState tus = pass.CreateTextureUnitState(textureName);
tus.SetTextureAddressingMode(TextureUnitState.TextureAddressingMode.TAM_CLAMP);
pass.AddTextureUnitState(tus);
_dynamicMaterial.Dispose();
ManualObject manualObject = Smgr.CreateManualObject(Guid.NewGuid().ToString());
manualObject.EstimateIndexCount(6);
manualObject.EstimateVertexCount(6);
manualObject.Begin(matNam, RenderOperation.OperationTypes.OT_TRIANGLE_LIST);
int yWidthVariable = bitmap.Width;
int xWidth = bitmap.Height;
manualObject.Position(new Vector3(0, 0, 0));
manualObject.TextureCoord(1, 0);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.Position(new Vector3(0, -yWidthVariable, 0));
manualObject.TextureCoord(0, 0f);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.Position(new Vector3(xWidth, 0, 0));
manualObject.TextureCoord(1f, 1);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.Position(new Vector3(0, -yWidthVariable, 0));
manualObject.TextureCoord(0f, 0f);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.Position(new Vector3(xWidth, -yWidthVariable, 0));
manualObject.TextureCoord(0f, 1.0f);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.Position(new Vector3(xWidth, 0, 0));
manualObject.TextureCoord(1f, 1.0f);
manualObject.Normal(Vector3.UNIT_Z);
manualObject.End();
manualObject.CastShadows = false;
return manualObject;
}
这段代码首先创建了一个包含文本的位图，然后创建了一个纹理，并将其应用到一个材质上。接着，它创建了一个ManualObject，这是一个可以在场景中渲染的自定义几何体。最后，它设置了ManualObject的一些属性，比如不投射阴影，并返回了这个对象。
可以通过ManualObject的BoundingBox属性来获取标签的大小。例如：
manualObject.BoundingBox.Size.x * 0.5f * Vector3.UNIT_Y;