GL: this TimeQuery test was just dumb.

Ah the good old times where my brain was not overflowing with
unnecessarily deep knowledge about how GPUs (and OpenGL drivers in
particular) work. Nope, switching a blend state and calling glFinish()
won't generate any GPU work, that will be all deferred until there's
something to be actually drawn, cleared or copied.

src/Magnum/GL/Test/TimeQueryGLTest.cpp

@@ -27,7 +27,10 @@
 
 #include "Magnum/GL/Context.h"
 #include "Magnum/GL/Extensions.h"
+#include "Magnum/GL/Framebuffer.h"
 #include "Magnum/GL/OpenGLTester.h"
+#include "Magnum/GL/Renderbuffer.h"
+#include "Magnum/GL/RenderbufferFormat.h"
 #include "Magnum/GL/TimeQuery.h"
 
 namespace Magnum { namespace GL { namespace Test { namespace {
@@ -105,22 +108,37 @@ void TimeQueryGLTest::queryTime() {
         CORRADE_SKIP(Extensions::EXT::disjoint_timer_query::string() + std::string(" is not available"));
     #endif
 
+    Renderbuffer renderbuffer;
+    renderbuffer.setStorage(
+        #ifndef MAGNUM_TARGET_GLES2
+        RenderbufferFormat::RGBA8,
+        #else
+        RenderbufferFormat::RGBA4,
+        #endif
+        Vector2i(32));
+
+    Framebuffer framebuffer({{}, Vector2i{256, 256}});
+    framebuffer.attachRenderbuffer(Framebuffer::ColorAttachment(0), renderbuffer);
+
+    /* A query with nothing inside should be almost zero */
     TimeQuery q1{TimeQuery::Target::TimeElapsed};
     q1.begin();
     q1.end();
-    const auto result1 = q1.result<UnsignedInt>();
+    const auto result1 = q1.result<UnsignedLong>();
-
     MAGNUM_VERIFY_NO_GL_ERROR();
+    Debug{} << "Doing nothing took" << result1/1.0e6f << "ms";
+    CORRADE_COMPARE_AS(result1, 0, TestSuite::Compare::GreaterOrEqual);
 
+    /* A query with a clear inside should be nonzero and larger than nothing */
     TimeQuery q2{TimeQuery::Target::TimeElapsed};
     q2.begin();
-    Renderer::enable(Renderer::Feature::Blending);
+    framebuffer.clear(FramebufferClear::Color);
-    Renderer::finish();
     q2.end();
-    const auto result2 = q2.result<UnsignedInt>();
+    const auto result2 = q2.result<UnsignedLong>();
-
     MAGNUM_VERIFY_NO_GL_ERROR();
-    CORRADE_COMPARE_AS(result2, result1, TestSuite::Compare::GreaterOrEqual);
+    Debug{} << "Clear took" << result2/1.0e6f << "ms";
+    CORRADE_VERIFY(result2);
+    CORRADE_COMPARE_AS(result2, result1, TestSuite::Compare::Greater);
 }
 
 void TimeQueryGLTest::queryTimestamp() {
@@ -135,6 +153,18 @@ void TimeQueryGLTest::queryTimestamp() {
         CORRADE_SKIP(Extensions::EXT::disjoint_timer_query::string() + std::string(" is not available"));
     #endif
 
+    Renderbuffer renderbuffer;
+    renderbuffer.setStorage(
+        #ifndef MAGNUM_TARGET_GLES2
+        RenderbufferFormat::RGBA8,
+        #else
+        RenderbufferFormat::RGBA4,
+        #endif
+        Vector2i(32));
+
+    Framebuffer framebuffer({{}, Vector2i{256, 256}});
+    framebuffer.attachRenderbuffer(Framebuffer::ColorAttachment(0), renderbuffer);
+
     TimeQuery q1{TimeQuery::Target::Timestamp},
         q2{TimeQuery::Target::Timestamp},
         q{TimeQuery::Target::TimeElapsed};
@@ -142,19 +172,23 @@ void TimeQueryGLTest::queryTimestamp() {
     q1.timestamp();
 
     q.begin();
-    Renderer::enable(Renderer::Feature::Blending);
+    framebuffer.clear(FramebufferClear::Color);
-    Renderer::finish();
     q.end();
 
     q2.timestamp();
 
-    const auto result = q.result<UnsignedInt>();
+    const auto result = q.result<UnsignedLong>();
     const auto result1 = q1.result<UnsignedLong>();
     const auto result2 = q2.result<UnsignedLong>();
-
     MAGNUM_VERIFY_NO_GL_ERROR();
-    CORRADE_COMPARE_AS(result2, result1, TestSuite::Compare::GreaterOrEqual);
+
-    CORRADE_COMPARE_AS(result2 - result1, result, TestSuite::Compare::GreaterOrEqual);
+    Debug{} << "Clear took" << result/1.0e6f << "ms, timestamp difference is"
+        << (result2 - result1)/1.0e6f << "ms";
+
+    /* The timestamps should be monotonically increasing and the difference
+       slightly larger than the elapsed time because these are outside of it */
+    CORRADE_COMPARE_AS(result2, result1, TestSuite::Compare::Greater);
+    CORRADE_COMPARE_AS(result2 - result1, result, TestSuite::Compare::Greater);
 }
 
 }}}}