From 32210bc3b32ee00475d707ae536f09869ab09cd7 Mon Sep 17 00:00:00 2001
From: Lars Ivar Hatledal <laht@ntnu.no>
Date: Wed, 20 Mar 2024 12:59:02 +0100
Subject: [PATCH] make it possible change the amount of instances to render
 (#247)

---
 examples/objects/instancing.cpp           | 21 +++++++++++----------
 include/threepp/objects/InstancedMesh.hpp |  9 +++++----
 src/threepp/objects/InstancedMesh.cpp     |  9 +++++++--
 3 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/examples/objects/instancing.cpp b/examples/objects/instancing.cpp
index 0d7734a27..f48ff14ff 100644
--- a/examples/objects/instancing.cpp
+++ b/examples/objects/instancing.cpp
@@ -29,6 +29,8 @@ namespace {
                 }
             }
         }
+        mesh.instanceMatrix()->needsUpdate();
+        mesh.instanceColor()->needsUpdate();
     }
 
 }// namespace
@@ -36,6 +38,7 @@ namespace {
 int main() {
 
     int amount = 10;
+    const int maxAmount = 25;
 
     Canvas canvas("Instancing", {{"aa", 4}, {"vsync", false}});
     GLRenderer renderer(canvas.size());
@@ -44,7 +47,7 @@ int main() {
 
     auto scene = Scene::create();
     auto camera = PerspectiveCamera::create(60, canvas.aspect(), 0.1f, 10000);
-    camera->position.set(float(amount), float(amount), float(amount));
+    camera->position.set(float(maxAmount), float(maxAmount), float(maxAmount));
 
     OrbitControls controls{*camera, canvas};
 
@@ -54,8 +57,9 @@ int main() {
 
     auto material = MeshPhongMaterial::create();
     auto geometry = IcosahedronGeometry::create(0.5f, 2);
-    auto mesh = InstancedMesh::create(geometry, material, static_cast<int>(std::pow(amount, 3)));
-
+    auto mesh = InstancedMesh::create(geometry, material, static_cast<int>(std::pow(maxAmount, 3)));
+    mesh->instanceMatrix()->setUsage(DrawUsage::Dynamic);
+    mesh->setCount(static_cast<int>(std::pow(amount, 3)));
     setupInstancedMesh(*mesh, amount);
     scene->add(mesh);
 
@@ -68,14 +72,11 @@ int main() {
         ImGui::SetNextWindowSize({width, 0}, 0);
 
         ImGui::Begin("Settings");
-        ImGui::SliderInt("Amount", &amount, 2, 25);
+        ImGui::SliderInt("Amount", &amount, 2, maxAmount);
         if (ImGui::IsItemEdited()) {
             colorMap.clear();
-            mesh->removeFromParent();
-            mesh = InstancedMesh::create(geometry, material, static_cast<int>(std::pow(amount, 3)));
+            mesh->setCount(static_cast<int>(std::pow(amount, 3)));
             setupInstancedMesh(*mesh, amount);
-            scene->add(mesh);
-            camera->position.set(float(amount), float(amount), float(amount));
         }
 
         ImGui::End();
@@ -93,7 +94,7 @@ int main() {
     const auto font = *fontLoader.load("data/fonts/helvetiker_regular.typeface.json");
 
     TextGeometry::Options opts(font, 20, 2);
-    auto handle = Text2D(opts, "");
+    auto handle = Text2D(opts);
     handle.setColor(Color::black);
     hud.add(handle, HUD::Options()
                             .setNormalizedPosition({0, 1})
@@ -135,7 +136,7 @@ int main() {
 
         counter.update(clock.getElapsedTime());
         if (it++ % 60 == 0) {
-            handle.setText("FPS: " + std::to_string(counter.fps), opts);
+            handle.setText("FPS: " + std::to_string(counter.fps));
             hud.needsUpdate(handle);
         }
 
diff --git a/include/threepp/objects/InstancedMesh.hpp b/include/threepp/objects/InstancedMesh.hpp
index 83a075bf4..3882fdf5d 100644
--- a/include/threepp/objects/InstancedMesh.hpp
+++ b/include/threepp/objects/InstancedMesh.hpp
@@ -12,7 +12,6 @@ namespace threepp {
     class InstancedMesh: public Mesh {
 
     public:
-
         InstancedMesh(
                 std::shared_ptr<BufferGeometry> geometry,
                 std::shared_ptr<Material> material,
@@ -20,9 +19,11 @@ namespace threepp {
 
         [[nodiscard]] size_t count() const;
 
-        FloatBufferAttribute* instanceMatrix() const;
+        void setCount(size_t count);
+
+        [[nodiscard]] FloatBufferAttribute* instanceMatrix() const;
 
-        FloatBufferAttribute* instanceColor() const;
+        [[nodiscard]] FloatBufferAttribute* instanceColor() const;
 
         [[nodiscard]] std::string type() const override;
 
@@ -50,9 +51,9 @@ namespace threepp {
         bool disposed{false};
 
         size_t count_;
+        size_t maxCount_;
         std::unique_ptr<FloatBufferAttribute> instanceMatrix_;
         std::unique_ptr<FloatBufferAttribute> instanceColor_ = nullptr;
-
     };
 
 }// namespace threepp
diff --git a/src/threepp/objects/InstancedMesh.cpp b/src/threepp/objects/InstancedMesh.cpp
index 96aa7ee43..5fba70d4d 100644
--- a/src/threepp/objects/InstancedMesh.cpp
+++ b/src/threepp/objects/InstancedMesh.cpp
@@ -22,7 +22,7 @@ InstancedMesh::InstancedMesh(
         std::shared_ptr<Material> material,
         size_t count)
     : Mesh(std::move(geometry), std::move(material)),
-      count_(count), instanceMatrix_(FloatBufferAttribute::create(std::vector<float>(count * 16), 16)) {
+      count_(count), maxCount_(count), instanceMatrix_(FloatBufferAttribute::create(std::vector<float>(count * 16), 16)) {
 
     this->frustumCulled = false;
 }
@@ -32,6 +32,11 @@ size_t InstancedMesh::count() const {
     return count_;
 }
 
+void InstancedMesh::setCount(size_t count) {
+
+    count_ = std::min(maxCount_, count);
+}
+
 FloatBufferAttribute* InstancedMesh::instanceMatrix() const {
 
     return instanceMatrix_.get();
@@ -62,7 +67,7 @@ void InstancedMesh::setColorAt(size_t index, const Color& color) {
 
     if (!this->instanceColor_) {
 
-        this->instanceColor_ = FloatBufferAttribute ::create(std::vector<float>(count_ * 3), 3);
+        this->instanceColor_ = FloatBufferAttribute ::create(std::vector<float>(maxCount_ * 3), 3);
     }
 
     color.toArray(this->instanceColor_->array(), index * 3);