add option to set ground plane location in world coords

include/polyscope/options.h

@@ -64,8 +64,10 @@ extern bool hideWindowAfterShow;
 
 // Behavior of the ground plane
 extern GroundPlaneMode groundPlaneMode;
+extern GroundPlaneHeightMode groundPlaneHeightMode;
 extern bool groundPlaneEnabled; // deprecated, but kept and respected for compatability. use groundPlaneMode.
 extern ScaledValue<float> groundPlaneHeightFactor;
+extern float groundPlaneHeight;
 extern int shadowBlurIters;
 extern float shadowDarkness;
 

include/polyscope/types.h

@@ -13,6 +13,7 @@ enum class BackgroundView { None = 0 };
 enum class ProjectionMode { Perspective = 0, Orthographic };
 enum class TransparencyMode { None = 0, Simple, Pretty };
 enum class GroundPlaneMode { None, Tile, TileReflection, ShadowOnly };
+enum class GroundPlaneHeightMode { Relative = 0, Absolute };
 enum class BackFacePolicy { Identical, Different, Custom, Cull };
 
 enum class PointRenderMode { Sphere = 0, Quad };

src/options.cpp

@@ -31,7 +31,9 @@ std::string screenshotExtension = ".png";
 // Ground plane / shadows
 bool groundPlaneEnabled = true;
 GroundPlaneMode groundPlaneMode = GroundPlaneMode::TileReflection;
+GroundPlaneHeightMode groundPlaneHeightMode = GroundPlaneHeightMode::Relative;
 ScaledValue<float> groundPlaneHeightFactor = 0;
+float groundPlaneHeight = 0.;
 int shadowBlurIters = 2;
 float shadowDarkness = 0.25;
 

src/render/ground_plane.cpp

@@ -196,7 +196,18 @@ void GroundPlane::draw(bool isRedraw) {
   double bboxBottom = sign == 1.0 ? std::get<0>(state::boundingBox)[iP] : std::get<1>(state::boundingBox)[iP];
   double bboxHeight = std::get<1>(state::boundingBox)[iP] - std::get<0>(state::boundingBox)[iP];
   double heightEPS = state::lengthScale * 1e-4;
-  double groundHeight = bboxBottom - sign * (options::groundPlaneHeightFactor.asAbsolute() + heightEPS);
+
+  double groundHeight = -777;
+  switch (options::groundPlaneHeightMode) {
+  case GroundPlaneHeightMode::Relative: {
+    groundHeight = bboxBottom - sign * (options::groundPlaneHeightFactor.asAbsolute() + heightEPS);
+    break;
+  }
+  case GroundPlaneHeightMode::Absolute: {
+    groundHeight = options::groundPlaneHeight;
+    break;
+  }
+  }
 
   // Viewport
   glm::vec4 viewport = render::engine->getCurrentViewport();
@@ -387,6 +398,16 @@ void GroundPlane::buildGui() {
     return "";
   };
 
+  auto heightModeName = [](const GroundPlaneHeightMode& m) -> std::string {
+    switch (m) {
+    case GroundPlaneHeightMode::Relative:
+      return "Relative";
+    case GroundPlaneHeightMode::Absolute:
+      return "Absolute";
+    }
+    return "";
+  };
+
   ImGui::SetNextItemOpen(false, ImGuiCond_FirstUseEver);
   if (ImGui::TreeNode("Ground Plane")) {
 
@@ -404,7 +425,39 @@ void GroundPlane::buildGui() {
     }
     ImGui::PopItemWidth();
 
-    if (ImGui::SliderFloat("Height", options::groundPlaneHeightFactor.getValuePtr(), -1.0, 1.0)) requestRedraw();
+    // Height
+    ImGui::PushItemWidth(80);
+    switch (options::groundPlaneHeightMode) {
+    case GroundPlaneHeightMode::Relative:
+      if (ImGui::SliderFloat("##HeightValue", options::groundPlaneHeightFactor.getValuePtr(), -1.0, 1.0))
+        requestRedraw();
+      break;
+    case GroundPlaneHeightMode::Absolute:
+      int iP;
+      float sign;
+      std::tie(iP, sign) = getGroundPlaneAxisAndSign();
+      double bboxBottom = sign == 1.0 ? std::get<0>(state::boundingBox)[iP] : std::get<1>(state::boundingBox)[iP];
+      double bboxHeight = std::get<1>(state::boundingBox)[iP] - std::get<0>(state::boundingBox)[iP];
+      if (ImGui::SliderFloat("##HeightValue", &options::groundPlaneHeight, bboxBottom - 0.5 * bboxHeight,
+                             bboxBottom + bboxHeight)) {
+        requestRedraw();
+      }
+      break;
+    }
+    ImGui::PopItemWidth();
+    ImGui::SameLine();
+    ImGui::PushItemWidth(100);
+    if (ImGui::BeginCombo("Height##Mode", heightModeName(options::groundPlaneHeightMode).c_str())) {
+      for (GroundPlaneHeightMode m : {GroundPlaneHeightMode::Relative, GroundPlaneHeightMode::Absolute}) {
+        std::string mName = heightModeName(m);
+        if (ImGui::Selectable(mName.c_str(), options::groundPlaneHeightMode == m)) {
+          options::groundPlaneHeightMode = m;
+          requestRedraw();
+        }
+      }
+      ImGui::EndCombo();
+    }
+    ImGui::PopItemWidth();
 
     switch (options::groundPlaneMode) {
     case GroundPlaneMode::None:

test/src/basics_test.cpp

@@ -134,5 +134,12 @@ TEST_F(PolyscopeTest, GroundPlaneTest) {
   polyscope::refresh();
   polyscope::show(3);
 
+  polyscope::options::groundPlaneHeightMode = polyscope::GroundPlaneHeightMode::Absolute;
+  polyscope::options::groundPlaneHeight = -0.3;
+  polyscope::show(3);
+
+  polyscope::options::groundPlaneHeightMode = polyscope::GroundPlaneHeightMode::Relative;
+  polyscope::show(3);
+
   polyscope::removeAllStructures();
 }