VectorDraw Developer Framework（VDF）是一个用于应用程序可视化的图形引擎库。有了VDF提供的功能，您可以轻松地创建、编辑、管理、输出、输入和打印2D和3D图形文件。
问：
如何在3D视图中检查对象是否隐藏在另一个对象中？例如，我有两个多面体，一个是z = 100的大面积，另一个是z = 0的面，并且视图是只有一个多面体是可见的，另一个多面体是在大面体后面，并且是完全看不见的在屏幕上。
答：
你需要一些OpenGL代码来检查一个对象是否落后于另一个对象（不可见）。
您需要的代码如下：
vdPolyface purple; // this is the polyface to check if is behind the green polyface
void test()
{ // just create the objects
vdPolyface pf1 = new vdPolyface(doc);
pf1.CreateBox(new gPoint(0, 0), 1, 1, 1, 0);
pf1.PenColor = new vdColor(Color.Purple);
doc.Model.Entities.AddItem(pf1);
purple = pf1; // this is the polyface to check if is behind the green polyface
vdPolyface pf2 = new vdPolyface(doc);
pf2.CreateBox(new gPoint(-2, 2), 4, 4, 4, 0);
pf2.PenColor = new vdColor(Color.Green);
doc.Model.Entities.AddItem(pf2); // this is the green polyface that hides the purple one
doc.RenderMode = vdRender.Mode.Shade;
//doc.CommandAction.View3D("VINW");
doc.CommandAction.View3D("VINE");
}
bool IsObjectVisible = false;
void test1() // this is the method that checks the “visibility” using the OnDrawAfter event
{
IsObjectVisible = false;
doc.OnDrawAfter += new vdDocument.DrawAfterEventHandler(TestObjectVisibility_OnDrawAfter);
doc.RenderMode = vdRender.Mode.Shade;
doc.Redraw(true);
doc.OnDrawAfter -= new vdDocument.DrawAfterEventHandler(TestObjectVisibility_OnDrawAfter);
MessageBox.Show(IsObjectVisible ? "Object is visible" : "Object is not visible");
}
void TestObjectVisibility_OnDrawAfter(object sender, vdRender render)
{
double[] _modelMatrix = new double[16], _projMatrix = new double[16];
int[] _viewport = new int[4];
double pwinx = 0.0, pwiny = 0.0, pwinz = 0.0;
//GET the active world to view and view to pixel matrixes
VectorDraw.Render.OpenGL.OpenGLImports.glGetDoublev(VectorDraw.Render.OpenGL.OpenGLImports.Parameters.GL_PROJECTION_MATRIX, _projMatrix);
VectorDraw.Render.OpenGL.OpenGLImports.glGetDoublev(VectorDraw.Render.OpenGL.OpenGLImports.Parameters.GL_MODELVIEW_MATRIX, _modelMatrix);
VectorDraw.Render.OpenGL.OpenGLImports.glGetIntegerv(VectorDraw.Render.OpenGL.OpenGLImports.Parameters.GL_VIEWPORT, _viewport);
Rectangle winrc = new Rectangle(_viewport[0], _viewport[1], _viewport[2], _viewport[3]);
foreach (gPoint pt in purple.VertexList)
{
VectorDraw.Render.OpenGL.OpenGLImports.gluProject(pt.x, pt.y, pt.z, _modelMatrix, _projMatrix, _viewport, ref pwinx, ref pwiny, ref pwinz);
Point winPt = new Point((int)pwinx, (int)pwiny);
if (!winrc.Contains(winPt)) continue;
//Get the existing depth in previous calculated pixel
double depth = VectorDraw.Render.OpenGL.OpenGLImports.glReadPixelDepth((int)(pwinx), (int)(pwiny));
//the pt is visible if the pwinz is smaller than the existing(it is closest to eye)
double def = pwinz - depth;
if (def <= 0.000001)
{
IsObjectVisible = true;
break;
}
}
}