GL: don't implicitly enable debug output in OpenGLTester.

It's just too spammy and we have a nice opt-in way now, so direct users to
use that instead.

doc/changelog.dox

@@ -308,6 +308,11 @@ See also:
     from flags passed to `eglCreateContext()` as that otherwise causes NVidia
     to fail with `EGL_BAD_MATCH`. See @ref opengl-workarounds for more
     information.
+-   @ref GL::OpenGLTester no longer implicitly enables @ref GL::DebugOutput as
+    it can be quite spammy when complex shaders or benchmarks are allowed. For
+    easier debugging, users are encouraged to use the new
+    `--magnum-gpu-validation` @ref GL-Context-command-line "command line option"
+    instead.
 
 @subsubsection changelog-latest-changes-math Math library
 

src/Magnum/GL/OpenGLTester.cpp

@@ -35,28 +35,7 @@
 
 namespace Magnum { namespace GL {
 
-OpenGLTester::OpenGLTester(): TestSuite::Tester{TestSuite::Tester::TesterConfiguration{}.setSkippedArgumentPrefixes({"magnum"})}, _windowlessApplication{{arguments().first, arguments().second}} {
-    /* Try to create debug context, fallback to normal one if not possible. No
-       such thing on macOS, iOS or WebGL. */
-    #if !defined(CORRADE_TARGET_APPLE) && !defined(MAGNUM_TARGET_WEBGL)
-    if(!_windowlessApplication.tryCreateContext(Platform::WindowlessApplication::Configuration{}.addFlags(Platform::WindowlessApplication::Configuration::Flag::Debug)))
-        _windowlessApplication.createContext();
-    #else
-    _windowlessApplication.createContext();
-    #endif
-
-    #ifndef MAGNUM_TARGET_WEBGL
-    if(Context::current().isExtensionSupported<Extensions::KHR::debug>()) {
-        Renderer::enable(Renderer::Feature::DebugOutput);
-        Renderer::enable(Renderer::Feature::DebugOutputSynchronous);
-        DebugOutput::setDefaultCallback();
-
-        /* Disable "Buffer detailed info" message on NV (too spammy) */
-        if(Context::current().detectedDriver() & Context::DetectedDriver::NVidia)
-            DebugOutput::setEnabled(DebugOutput::Source::Api, DebugOutput::Type::Other, {131185}, false);
-    }
-    #endif
-}
+OpenGLTester::OpenGLTester(): TestSuite::Tester{TestSuite::Tester::TesterConfiguration{}.setSkippedArgumentPrefixes({"magnum"})}, _windowlessApplication{{arguments().first, arguments().second}} {}
 
 OpenGLTester::~OpenGLTester() = default;
 

src/Magnum/GL/OpenGLTester.h

@@ -121,16 +121,14 @@ to run single isolated test cases.
 
 @section GL-OpenGLTester-debug Debug context and error checking
 
-On platforms that support it, the OpenGL context is created with synchronous
-debug output, meaning that every OpenGL error is directly reported to standard
-output. While it is possible, the tester class doesn't abort the test cases
-upon encountering a GL error --- this should be done explicitly with
-@ref MAGNUM_VERIFY_NO_GL_ERROR() instead, as the debug output is not available
-on all platforms and not all GL errors are fatal.
-
-@note This overrides the `--magnum-gpu-validation`
-    @ref GL-Context-command-line "command line option", making it always
-    enabled.
+Because @ref DebugOutput can be quite spammy in some cases, especially when
+compiling more complex shaders or doing benchmarks, it's not implicitly enabled
+by default to make the test output more readable. Instead of relying on debug
+output to report errors, the @ref MAGNUM_VERIFY_NO_GL_ERROR() macro should be
+used to reliably check for errors regardless of platform support. For easier
+debugging of OpenGL errors users are encuraged to use the
+`--magnum-gpu-validation` @ref GL-Context-command-line "command line option",
+which is supported here as well as in all other application implementations.
 
 @section GL-OpenGLTester-benchmarks GPU time benchmarks
 
@@ -263,12 +261,8 @@ class OpenGLTester: public TestSuite::Tester {
         #endif
 
         struct WindowlessApplication: Platform::WindowlessApplication {
-            explicit WindowlessApplication(const Arguments& arguments): Platform::WindowlessApplication{arguments, NoCreate} {}
+            explicit WindowlessApplication(const Arguments& arguments): Platform::WindowlessApplication{arguments} {}
             int exec() override final { return 0; }
-
-            using Platform::WindowlessApplication::tryCreateContext;
-            using Platform::WindowlessApplication::createContext;
-
         } _windowlessApplication;
 
         #ifndef MAGNUM_TARGET_WEBGL

src/Magnum/GL/Test/DebugOutputGLTest.cpp

@@ -73,7 +73,6 @@ void DebugOutputGLTest::setCallbackDefault() {
     if(!Context::current().isExtensionSupported<Extensions::KHR::debug>())
         CORRADE_SKIP(Extensions::KHR::debug::string() + std::string(" is not supported"));
 
-    /* Need to be careful, because the test runner is using debug output too */
     DebugOutput::setDefaultCallback();
 
     MAGNUM_VERIFY_NO_GL_ERROR();
@@ -82,15 +81,23 @@ void DebugOutputGLTest::setCallbackDefault() {
 void DebugOutputGLTest::setup() {
     _out.str({});
 
-    if(Context::current().isExtensionSupported<Extensions::KHR::debug>())
-        DebugOutput::setCallback([](DebugOutput::Source source, DebugOutput::Type type, UnsignedInt id, DebugOutput::Severity severity, const std::string& string, const void* userPtr) {
-            Implementation::defaultDebugCallback(source, type, id, severity, string, static_cast<std::ostringstream*>(const_cast<void*>(userPtr)));
-        }, &_out);
+    if(!Context::current().isExtensionSupported<Extensions::KHR::debug>())
+        return;
+
+    Renderer::enable(Renderer::Feature::DebugOutput);
+    Renderer::enable(Renderer::Feature::DebugOutputSynchronous);
+    DebugOutput::setCallback([](DebugOutput::Source source, DebugOutput::Type type, UnsignedInt id, DebugOutput::Severity severity, const std::string& string, const void* userPtr) {
+        Implementation::defaultDebugCallback(source, type, id, severity, string, static_cast<std::ostringstream*>(const_cast<void*>(userPtr)));
+    }, &_out);
 }
 
 void DebugOutputGLTest::teardown() {
-    if(Context::current().isExtensionSupported<Extensions::KHR::debug>())
-        DebugOutput::setDefaultCallback();
+    if(!Context::current().isExtensionSupported<Extensions::KHR::debug>())
+        return;
+
+    Renderer::disable(Renderer::Feature::DebugOutput);
+    Renderer::disable(Renderer::Feature::DebugOutputSynchronous);
+    DebugOutput::setDefaultCallback();
 }
 
 void DebugOutputGLTest::setEnabled() {