From d20f5688362e0b8e342e6866d8ed83189b468883 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Fri, 13 Apr 2018 13:21:30 +0200
Subject: [PATCH] Use GLUT for detecting errors.

Rather than polling for errors, let GLUT do it. Can be enabled with the
"-gldebug" CLI flag.
---
 src/fmri/ActivityAnimation.cpp |  1 -
 src/fmri/RenderingState.cpp    |  2 --
 src/fmri/glutils.cpp           | 41 ++++++++++++++++++++--------------
 src/fmri/glutils.hpp           | 10 ++++-----
 src/fmri/main.cpp              |  3 +++
 5 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/src/fmri/ActivityAnimation.cpp b/src/fmri/ActivityAnimation.cpp
index 22380e7..8b58b0f 100644
--- a/src/fmri/ActivityAnimation.cpp
+++ b/src/fmri/ActivityAnimation.cpp
@@ -78,7 +78,6 @@ void ActivityAnimation::draw(float timeScale)
         glColor4fv(RenderingState::instance().pathColor().data());
         glVertexPointer(3, GL_FLOAT, 0, startingPos.data());
         glDrawElements(GL_LINES, lineIndices.size(), GL_UNSIGNED_INT, lineIndices.data());
-        checkGLErrors();
     }
     glDisableClientState(GL_VERTEX_ARRAY);
 }
diff --git a/src/fmri/RenderingState.cpp b/src/fmri/RenderingState.cpp
index a065989..5e3f6b3 100644
--- a/src/fmri/RenderingState.cpp
+++ b/src/fmri/RenderingState.cpp
@@ -481,8 +481,6 @@ void RenderingState::idleFunc()
         if (options.mouse_2_pressed) {
             move('s', false);
         }
-
-        checkGLErrors();
         throttleIdleFunc();
     }
     glutPostRedisplay();
diff --git a/src/fmri/glutils.cpp b/src/fmri/glutils.cpp
index 34a23ee..9d30cd4 100644
--- a/src/fmri/glutils.cpp
+++ b/src/fmri/glutils.cpp
@@ -7,19 +7,13 @@
 #include <thread>
 #include "glutils.hpp"
 
+#ifdef FREEGLUT
+#include <GL/freeglut.h>
+#endif
+
 using namespace fmri;
 using namespace std;
 
-static void handleGLError(GLenum error) {
-    switch (error) {
-        case GL_NO_ERROR:
-            return;
-
-        default:
-            cerr << "OpenGL error: " << (const char*) gluGetString(error) << endl;
-    }
-}
-
 void fmri::changeWindowSize(int w, int h)
 {
     // Prevent a divide by zero, when window is too short
@@ -59,13 +53,6 @@ void fmri::renderText(std::string_view text, int x, int y)
     }
 }
 
-void fmri::checkGLErrors()
-{
-    while (auto error = glGetError()) {
-        handleGLError(error);
-    }
-}
-
 void fmri::throttleIdleFunc()
 {
     using namespace std::chrono;
@@ -129,3 +116,23 @@ void fmri::drawImageTiles(int n, const float *vertexBuffer, const float *texture
     glDisableClientState(GL_VERTEX_ARRAY);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
 }
+
+
+void fmri::registerErrorCallbacks()
+{
+#ifdef FREEGLUT
+    glutInitErrorFunc([](const char* format, va_list args) {
+        char buffer[1024];
+        std::vsnprintf(buffer, sizeof(buffer), format, args);
+        LOG(ERROR) << "freeglut: " << buffer;
+    });
+    glutInitWarningFunc([](const char* format, va_list args) {
+        char buffer[1024];
+        std::vsnprintf(buffer, sizeof(buffer), format, args);
+        LOG(WARNING) << "freeglut: " << buffer;
+    });
+    LOG(INFO) << "Freeglut error handlers installed successfully";
+#else
+    LOG(INFO) << "Compiled without freeglut, error handlers not available.";
+#endif
+}
diff --git a/src/fmri/glutils.hpp b/src/fmri/glutils.hpp
index cc53f9d..8286d2e 100644
--- a/src/fmri/glutils.hpp
+++ b/src/fmri/glutils.hpp
@@ -29,11 +29,6 @@ namespace fmri {
      */
     void renderText(std::string_view text, int x = 0, int y = 0);
 
-    /**
-     * Check if there are OpenGL errors and report them.
-     */
-    void checkGLErrors();
-
     /**
      * Slow down until the idle func is being called a reasonable amount of times.
      */
@@ -55,4 +50,9 @@ namespace fmri {
      */
     void
     drawImageTiles(int n, const float *vertexBuffer, const float *textureCoords, const Texture &texture, float alpha);
+
+    /**
+     * Attempmt to register
+     */
+    void registerErrorCallbacks();
 }
diff --git a/src/fmri/main.cpp b/src/fmri/main.cpp
index f810f11..97e0c8d 100644
--- a/src/fmri/main.cpp
+++ b/src/fmri/main.cpp
@@ -3,6 +3,7 @@
 #include <glog/logging.h>
 #include <GL/glut.h>
 #include <map>
+#include <cstdarg>
 
 #include "LayerData.hpp"
 #include "Options.hpp"
@@ -54,6 +55,8 @@ int main(int argc, char *argv[])
     google::InitGoogleLogging(argv[0]);
     google::InstallFailureSignalHandler();
 
+    registerErrorCallbacks();
+
     glutInit(&argc, argv);
     glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA | GLUT_ALPHA);
     glutCreateWindow(argv[0]);