GL: make the ApiTrace viewport workaround no longer silent.

doc/changelog.dox

@@ -293,6 +293,11 @@ See also:
     @ref GL::Context::DetectedDriver::ArmMali "ARM Mali" drivers complain about
     R8 not being renderable (even though the format shouldn't matter when
     unbinding a texture)
+-   The engine was silently doing an explicit initial call to @fn_gl{Viewport}
+    when it detected it's running under ApiTrace, because otherwise ApiTrace
+    would assume a zero-sized framebuffer. This behavior is no longer silent
+    but advertised as a @cpp "apitrace-zero-initial-viewport" @ce workaround.
+    See @ref opengl-workarounds for more information.
 
 @subsubsection changelog-latest-changes-math Math library
 

src/Magnum/GL/DefaultFramebuffer.cpp

@@ -121,12 +121,6 @@ void DefaultFramebuffer::initializeContextBasedFunctionality(Context& context) {
     glGetIntegerv(GL_VIEWPORT, viewport);
     defaultFramebuffer._viewport = state.viewport = Range2Di::fromSize({viewport[0], viewport[1]}, {viewport[2], viewport[3]});
     CORRADE_INTERNAL_ASSERT(defaultFramebuffer._viewport != Implementation::FramebufferState::DisengagedViewport);
-
-    /* Fake initial glViewport() call for ApiTrace */
-    #ifndef MAGNUM_TARGET_GLES
-    if(context.isExtensionSupported<Extensions::GREMEDY::string_marker>())
-        glViewport(viewport[0], viewport[1], viewport[2], viewport[3]);
-    #endif
 }
 
 #ifndef DOXYGEN_GENERATING_OUTPUT

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -256,6 +256,12 @@ namespace {
    glGetFramebufferParameter() works correctly. */
 "nv-implementation-color-read-format-dsa-broken",
 #endif
+
+#ifndef MAGNUM_TARGET_GLES
+/* ApiTrace needs an explicit initial glViewport() call to initialize its
+   framebuffer size, otherwise it assumes it's zero-sized. */
+"apitrace-zero-initial-viewport",
+#endif
 /* [workarounds] */
     };
 }
@@ -431,6 +437,15 @@ void Context::setupDriverWorkarounds() {
     #endif
 
     #undef _setRequiredVersion
+
+    #ifndef MAGNUM_TARGET_GLES
+    if(isExtensionSupported<Extensions::GREMEDY::string_marker>() &&
+       !isDriverWorkaroundDisabled("apitrace-zero-initial-viewport")) {
+        GLint viewport[4];
+        glGetIntegerv(GL_VIEWPORT, viewport);
+        glViewport(viewport[0], viewport[1], viewport[2], viewport[3]);
+    }
+    #endif
 }
 
 }}