D3D标注动态避让

原来也思考了该如何实现标注动态避让，认为必须得计算字符串所占的大小。如果在屏幕上要计算屏幕象素之类的东西。

今天总算找到了实现方法，在C# WorldWind中的KMLImporter类中有。关键是Font的如下方法：

public Rectangle MeasureString(Sprite sprite, string text, DrawTextFormat format, Color color);

public Rectangle MeasureString(Sprite sprite, string text, DrawTextFormat format, int color);

 if(icon.Name != null)
                 {
                     // Render name field
                     const int labelWidth = ; // Dummy value needed for centering the text
                     if(iconTexture==null)
                     {
                         // Center over target as we have no bitmap
                         Rectangle realrect = drawArgs.defaultDrawingFont.MeasureString(m_sprite, icon.Name, DrawTextFormat.WordBreak, color);
                         realrect.X = (int)projectedPoint.X - (labelWidth>>);
                         realrect.Y = (int)(projectedPoint.Y - (drawArgs.defaultDrawingFont.Description.Height >> ));

                         bool bDraw = true;

                         foreach (Rectangle drawnrect in labelRectangles)
                         {
                             if (realrect.IntersectsWith(drawnrect))
                             {
                                 bDraw = false;
                                 break;
                             }
                         }

                         if (bDraw)
                         {
                             labelRectangles.Add(realrect);
                             drawArgs.defaultDrawingFont.DrawText(m_sprite, icon.Name, realrect, DrawTextFormat.Center, color);
                         }
                     }
                     else
                     {
                         // Adjust text to make room for icon
                         int spacing = (int)(icon.Width * 0.3f);
                         if(spacing>)
                             spacing = ;
                         int offsetForIcon = (icon.Width>>) + spacing;

                         // Text to the right
                         Rectangle rightrect = drawArgs.defaultDrawingFont.MeasureString(m_sprite, icon.Name, DrawTextFormat.WordBreak, color);
                         rightrect.X = (int)projectedPoint.X + offsetForIcon;
                         rightrect.Y = (int)(projectedPoint.Y - (drawArgs.defaultDrawingFont.Description.Height >> ));

                         // Text to the left
                         Rectangle leftrect = drawArgs.defaultDrawingFont.MeasureString(m_sprite, icon.Name, DrawTextFormat.WordBreak, color);
                         leftrect.X = (int)projectedPoint.X - offsetForIcon - rightrect.Width;
                         leftrect.Y = (int)(projectedPoint.Y - (drawArgs.defaultDrawingFont.Description.Height >> ));

                         bool bDrawRight = true;
                         bool bDrawLeft = true;

                         foreach (Rectangle drawnrect in labelRectangles)
                         {
                             if (rightrect.IntersectsWith(drawnrect))
                             {
                                 bDrawRight = false;
                             }
                             if (leftrect.IntersectsWith(drawnrect))
                             {
                                 bDrawLeft = false;
                             }
                             if (!bDrawRight && !bDrawLeft)
                             {
                                 break;
                             }
                         }

                         if (bDrawRight)
                         {
                             labelRectangles.Add(rightrect);
                             drawArgs.defaultDrawingFont.DrawText(m_sprite, icon.Name, rightrect, DrawTextFormat.WordBreak, color);
                         }
                         else if (bDrawLeft)
                         {
                             labelRectangles.Add(leftrect);
                             drawArgs.defaultDrawingFont.DrawText(m_sprite, icon.Name, leftrect, DrawTextFormat.WordBreak, color);
                         }
                     }
                 }

这种方式实现简单，但是会造成先添加到标注字符串集合的文字优先显示。索引靠后的文字始终被隐藏。