Implement a simple loading animation.

Loading currently doesn't happen, because loading tries to do some GL
actions which cannot happen in a background thread (in GLUT anyway).

TODO: move all GL options to the main thread, and leave the rest of the
loading to the background.

CMakeLists.txt

@@ -24,6 +24,7 @@ find_package(OpenGL REQUIRED)
 find_package(GLUT REQUIRED)
 find_package(Boost REQUIRED COMPONENTS filesystem program_options)
 find_package(OpenCV 3 REQUIRED COMPONENTS core imgproc imgcodecs)
+find_package(Threads REQUIRED)
 
 target_link_libraries(fmri PUBLIC
 	Caffe::Caffe
@@ -33,6 +34,7 @@ target_link_libraries(fmri PUBLIC
 	opencv_core
 	opencv_imgproc
 	opencv_imgcodecs
+	Threads::Threads
 	)
 
 target_include_directories(fmri PUBLIC

src/fmri/RenderingState.cpp

@@ -217,7 +217,17 @@ void RenderingState::loadSimulationData(const std::map<string, LayerInfo> &info,
     layerData = std::move(data);
     currentData = layerData.begin();
 
-    updateVisualisers();
+    queueUpdate();
+}
+
+void RenderingState::queueUpdate()
+{
+    loadingFuture = std::async(std::launch::async, []() {
+        // Currently causes a segfault, due to threaded OpenGL.
+        // Possible solution: don't do GL things while loading.
+        //RenderingState::instance().updateVisualisers();
+    });
+    isLoading = true;
 }
 
 void RenderingState::updateVisualisers()
@@ -249,8 +259,18 @@ void RenderingState::render(float time) const
     // Clear Color and Depth Buffers
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
-    configureRenderingContext();
+    if (!isLoading) {
+        renderVisualisation(time);
+    } else {
+        renderLoadingScreen();
+    }
 
+    glutSwapBuffers();
+}
+
+void RenderingState::renderVisualisation(float time) const
+{
+    configureRenderingContext();
 
     glPushMatrix();
 
@@ -275,8 +295,24 @@ void RenderingState::render(float time) const
     glPopMatrix();
 
     renderOverlayText();
+}
 
-    glutSwapBuffers();
+void RenderingState::renderLoadingScreen() const
+{
+    glLoadIdentity();
+    glTranslatef(0, 0, -4);
+    glRotatef(360 * getAnimationStep(std::chrono::seconds(4)), 0, 1, 0);
+    glColor3f(1, 1, 1);
+    glutWireTeapot(1);
+
+
+    auto pulse = std::cos(2 * M_PI * getAnimationStep(std::chrono::seconds(3)));
+    pulse *= pulse;
+    glColor3d(pulse, pulse, 0);
+    glLoadIdentity();
+    setOrthographicProjection();
+    renderText("Loading...", 5, 15);
+    restorePerspectiveProjection();
 }
 
 void RenderingState::drawLayer(float time, unsigned long i) const
@@ -341,7 +377,7 @@ void RenderingState::handleSpecialKey(int key)
                 currentData = layerData.end();
             }
             --currentData;
-            updateVisualisers();
+            queueUpdate();
             break;
 
         case GLUT_KEY_RIGHT:
@@ -349,7 +385,7 @@ void RenderingState::handleSpecialKey(int key)
             if (currentData == layerData.end()) {
                 currentData = layerData.begin();
             }
-            updateVisualisers();
+            queueUpdate();
             break;
 
         case GLUT_KEY_F1:
@@ -419,6 +455,23 @@ float RenderingState::layerAlpha() const
 
 void RenderingState::idleFunc()
 {
+    if (isLoading && loadingFuture.valid()) {
+        auto result = loadingFuture.wait_for(std::chrono::milliseconds(40));
+        switch (result) {
+            case std::future_status::deferred:
+                LOG(ERROR) << "loading status was deferred, invalid state!";
+                abort();
+
+            case std::future_status::timeout:
+                // Still loading
+                break;
+
+            case std::future_status::ready:
+                loadingFuture.get();
+                //isLoading = false;
+                break;
+        }
+    } else {
         if (options.mouse_1_pressed) {
             move('w', false);
         }
@@ -428,5 +481,6 @@ void RenderingState::idleFunc()
 
         checkGLErrors();
         throttleIdleFunc();
+    }
     glutPostRedisplay();
 }

src/fmri/RenderingState.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <string>
+#include <future>
 #include "LayerInfo.hpp"
 #include "LayerData.hpp"
 #include "LayerVisualisation.hpp"
@@ -78,6 +79,9 @@ namespace fmri
         std::vector<std::vector<LayerData>>::iterator currentData;
         std::vector<std::unique_ptr<LayerVisualisation>> layerVisualisations;
         std::vector<std::unique_ptr<Animation>> interactionAnimations;
+        bool isLoading = false;
+        std::future<void> loadingFuture;
+
 
         RenderingState() noexcept;
 
@@ -92,5 +96,11 @@ namespace fmri
         void renderLayerName(const std::string& name) const;
 
         void drawLayer(float time, unsigned long i) const;
+
+        void queueUpdate();
+
+        void renderLoadingScreen() const;
+
+        void renderVisualisation(float time) const;
     };
 }