Support for faces with holes in 3D

CHANGELOG

@@ -12,6 +12,9 @@
 Version 4.1.1 (development)
 ===========================
 
+- Added the option to cut a portion of the interiors of 3D faces to expose more
+  of the mesh. Useful as an alternative to transparency. See keys Ctrl+F3/F4.
+
 - Added 3D scene export to glTF format (https://www.khronos.org/gltf) which is
   bound to the key 'G'. This can be used to import GLVis scenes for rendering in
   Blender, as well as for augmented reality, see https://modelviewer.dev/editor.

lib/openglvis.cpp

@@ -126,6 +126,9 @@ VisualizationScene::VisualizationScene()
    ViewCenterX = 0.0;
    ViewCenterY = 0.0;
 
+   cut_lambda = 0.0;
+   cut_updated = false;
+
    background = BG_WHITE;
    GetAppWindow()->getRenderer().setClearColor(1.f, 1.f, 1.f, 1.f);
    _use_cust_l0_pos = false;
@@ -137,6 +140,116 @@ VisualizationScene::VisualizationScene()
 
 VisualizationScene::~VisualizationScene() {}
 
+
+void VisualizationScene
+:: DrawCutTriangle(gl3::GlDrawable& buff,
+                   const double (&p)[4][3], const double (&cv)[4],
+                   const double minv, const double maxv)
+{
+   // element center
+   double c[3];
+   c[0] = c[1] = c[2] = 0.0;
+   for (int j = 0; j < 3; j++)
+   {
+      c[0] += p[j][0]; c[1] += p[j][1]; c[2] += p[j][2];
+   }
+   c[0] /= 3.0; c[1] /= 3.0; c[2] /= 3.0;
+
+   double l = cut_lambda;
+   double q[3][3];
+
+   // corners of the cut frame
+   for (int j = 0; j < 3; j++)
+   {
+      q[j][0] = l*p[j][0] + (1.0-l)*c[0];
+      q[j][1] = l*p[j][1] + (1.0-l)*c[1];
+      q[j][2] = l*p[j][2] + (1.0-l)*c[2];
+   }
+
+   double d[4][3];
+   double cvv[4];
+
+   // bottom trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[0][k]; d[1][k] = p[1][k]; d[2][k] = q[1][k]; d[3][k] = q[0][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+
+   // diagonal trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[1][k]; d[1][k] = p[2][k]; d[2][k] = q[2][k]; d[3][k] = q[1][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+
+   // left trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[2][k]; d[1][k] = p[0][k]; d[2][k] = q[0][k]; d[3][k] = q[2][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+}
+
+
+void VisualizationScene
+:: DrawCutQuad(gl3::GlDrawable& buff,
+               const double (&p)[4][3], const double (&cv)[4],
+               const double minv, const double maxv)
+{
+   // element center
+   double c[3];
+   c[0] = c[1] = c[2] = 0.0;
+   for (int j = 0; j < 4; j++)
+   {
+      c[0] += p[j][0]; c[1] += p[j][1]; c[2] += p[j][2];
+   }
+   c[0] /= 4.0; c[1] /= 4.0; c[2] /= 4.0;
+
+   double l = cut_lambda;
+   double q[4][3];
+
+   // corners of the cut frame
+   for (int j = 0; j < 4; j++)
+   {
+      q[j][0] = l*p[j][0] + (1.0-l)*c[0];
+      q[j][1] = l*p[j][1] + (1.0-l)*c[1];
+      q[j][2] = l*p[j][2] + (1.0-l)*c[2];
+   }
+
+   double d[4][3];
+   double cvv[4];
+
+   // bottom trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[0][k]; d[1][k] = p[1][k]; d[2][k] = q[1][k]; d[3][k] = q[0][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+
+   // right trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[1][k]; d[1][k] = p[2][k]; d[2][k] = q[2][k]; d[3][k] = q[1][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+
+   // top trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[2][k]; d[1][k] = p[3][k]; d[2][k] = q[3][k]; d[3][k] = q[2][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+
+   // left trapezoid
+   for (int k = 0; k < 3; k++)
+   {
+      d[0][k] = p[3][k]; d[1][k] = p[0][k]; d[2][k] = q[0][k]; d[3][k] = q[3][k];
+   }
+   DrawQuad(buff, d, cvv, minv, maxv);
+}
+
+
 void VisualizationScene
 ::DrawTriangle(gl3::GlDrawable& buff,
                const double (&pts)[4][3], const double (&cv)[4],

lib/openglvis.hpp

@@ -88,7 +88,6 @@ class VisualizationScene
    int light_mat_idx;
    bool use_light;
 
-
    gl3::RenderParams GetMeshDrawParams();
    glm::mat4 GetModelViewMtx();
 
@@ -126,6 +125,20 @@ class VisualizationScene
                  const double (&pts)[4][3], const double (&cv)[4],
                  const double minv, const double maxv);
 
+   /// Draw a 3D triangle in physical space with a central triangle removed. The
+   /// cut is controlled by value of cut_lambda. See keys Ctrl+F3/F4. Similar to
+   /// CutReferenceTriangle in lib/vssolution3d.cpp.
+   void DrawCutTriangle(gl3::GlDrawable& buff,
+                        const double (&pts)[4][3], const double (&cv)[4],
+                        const double minv, const double maxv);
+
+   /// Draw a 3D quad in physical space with a central square removed. The cut
+   /// is controlled by the value of cut_lambda. See keys Ctrl+F3/F4. Similar to
+   /// CutReferenceSquare in lib/vssolution3d.cpp.
+   void DrawCutQuad(gl3::GlDrawable& buff,
+                    const double (&pts)[4][3], const double (&cv)[4],
+                    const double minv, const double maxv);
+
    void DrawPatch(gl3::GlDrawable& buff, const mfem::DenseMatrix &pts,
                   mfem::Vector &vals, mfem::DenseMatrix &normals,
                   const int n, const mfem::Array<int> &ind, const double minv,
@@ -167,6 +180,11 @@ class VisualizationScene
    /// Bounding box.
    double x[2], y[2], z[2];
 
+   /// Amount of face cutting with keys Ctrl-F3/F4 (0: no cut, 1: cut to edges)
+   double cut_lambda;
+   /// Have the reference geometries been updated for the cut?
+   bool cut_updated;
+
    glm::mat4 rotmat;
    glm::mat4 translmat;