Makes error reporting more communicative.

Outputs/OpenGL/OpenGL.hpp

@@ -9,6 +9,8 @@
 #ifndef OpenGL_h
 #define OpenGL_h
 
+#include <iostream>
+
 // TODO: figure out correct include paths for other platforms.
 #ifdef __APPLE__
 	#if TARGET_OS_IPHONE
@@ -22,14 +24,25 @@
 #include <GL/gl.h>
 #endif
 
-// To consider: might it be smarter to switch and log on error,
-// rather than raising an exception? They're conventionally
-// something you're permitted to ignore.
-//
-// (and, from that indecision, hence the pointless decision
-// on whether to use an assert based on NDEBUG)
 #ifndef NDEBUG
-#define test_gl_error() assert(!glGetError());
+
+#define test_gl_error() { \
+	const auto error = glGetError();	\
+	if(error) { \
+		switch(error) {	\
+			default:	std::cerr << "Error " << error;\
+			case GL_INVALID_ENUM: std::cerr << "GL_INVALID_ENUM"; break;	\
+			case GL_INVALID_VALUE: std::cerr << "GL_INVALID_VALUE"; break;	\
+			case GL_INVALID_OPERATION: std::cerr << "GL_INVALID_OPERATION"; break;	\
+			case GL_INVALID_FRAMEBUFFER_OPERATION: std::cerr << "GL_INVALID_FRAMEBUFFER_OPERATION"; break;	\
+			case GL_OUT_OF_MEMORY: std::cerr << "GL_OUT_OF_MEMORY"; break;	\
+		};	\
+		std::cerr << " at line " << __LINE__ << " in " << __FILE__ << std::endl;	\
+		assert(false);	\
+	}	\
+	\
+}
+
 #else
 #define test_gl_error() while(false) {}
 #endif