migrate UBOBindingsSaver class to px_vp20/utils

This workaround was originally extracted from the Pixar batch renderer and
turned into a more convenient and reusable RAII-style class. Since the
workaround it provides is needed in multiple places, it would be good to have
it defined publicly to take advantage of that reuse.

lib/render/mayaToHydra/renderOverride.cpp

@@ -47,6 +47,7 @@ PXR_NAMESPACE_CLOSE_SCOPE
 #include <chrono>
 #include <exception>
 
+#include "mayaUsd/render/px_vp20/utils.h"
 #include "../../usd/hdMaya/delegates/delegateRegistry.h"
 #include "../../usd/hdMaya/delegates/sceneDelegate.h"
 
@@ -107,48 +108,6 @@ class UfeSelectionObserver : public UFE_NS::Observer {
 
 #endif // WANT_UFE_BUILD
 
-/// Simple RAII class to save uniform buffer bindings, to deal with a maya
-/// issue.
-///
-/// As originally explained by Pixar in their usdmaya plugin:
-///
-/// XXX: When Maya is using OpenGL Core Profile as the rendering engine (in
-/// either compatibility or strict mode), batch renders like those done in
-/// the "Render View" window or through the ogsRender command do not
-/// properly track uniform buffer binding state. This was causing issues
-/// where the first batch render performed would look correct, but then all
-/// subsequent renders done in that Maya session would be completely black
-/// (no alpha), even if the frame contained only Maya-native geometry or if
-/// a new scene was created/opened.
-///
-/// To avoid this problem, we need to save and restore Maya's bindings
-/// across Hydra calls. We try not to bog down performance by saving and
-/// restoring *all* GL_MAX_UNIFORM_BUFFER_BINDINGS possible bindings, so
-/// instead we only do just enough to avoid issues. Empirically, the
-/// problematic binding has been the material binding at index 4.
-class UBOBindingsSaver {
-public:
-    static constexpr size_t UNIFORM_BINDINGS_TO_SAVE = 5u;
-
-    UBOBindingsSaver() {
-        for (size_t i = 0u; i < _uniformBufferBindings.size(); ++i) {
-            glGetIntegeri_v(
-                GL_UNIFORM_BUFFER_BINDING, (GLuint)i,
-                &_uniformBufferBindings[i]);
-        }
-    }
-
-    ~UBOBindingsSaver() {
-        for (size_t i = 0u; i < _uniformBufferBindings.size(); ++i) {
-            glBindBufferBase(
-                GL_UNIFORM_BUFFER, (GLuint)i, _uniformBufferBindings[i]);
-        }
-    }
-
-private:
-    std::array<GLint, UNIFORM_BINDINGS_TO_SAVE> _uniformBufferBindings;
-};
-
 } // namespace
 
 MtohRenderOverride::MtohRenderOverride(const MtohRendererDescription& desc)

lib/render/px_vp20/utils.cpp

@@ -27,6 +27,7 @@
 #include "pxr/base/gf/vec3f.h"
 #include "pxr/base/gf/vec4f.h"
 #include "pxr/base/tf/stringUtils.h"
+#include "pxr/imaging/garch/gl.h"
 #include "pxr/imaging/glf/simpleLight.h"
 #include "pxr/imaging/glf/simpleLightingContext.h"
 #include "pxr/imaging/glf/simpleMaterial.h"
@@ -1081,4 +1082,25 @@ px_vp20Utils::OutputDisplayStatusToStream(
 }
 
 
+UBOBindingsSaver::UBOBindingsSaver()
+{
+    for (size_t i = 0u; i < _uniformBufferBindings.size(); ++i) {
+        glGetIntegeri_v(
+            GL_UNIFORM_BUFFER_BINDING,
+            static_cast<GLuint>(i),
+            &_uniformBufferBindings[i]);
+    }
+}
+
+UBOBindingsSaver::~UBOBindingsSaver()
+{
+    for (size_t i = 0u; i < _uniformBufferBindings.size(); ++i) {
+        glBindBufferBase(
+            GL_UNIFORM_BUFFER,
+            static_cast<GLuint>(i),
+            _uniformBufferBindings[i]);
+    }
+}
+
+
 PXR_NAMESPACE_CLOSE_SCOPE

lib/render/px_vp20/utils.h

@@ -24,6 +24,7 @@
 #include "pxr/base/gf/matrix4d.h"
 #include "pxr/base/gf/matrix4f.h"
 #include "pxr/base/gf/vec4f.h"
+#include "pxr/imaging/garch/gl.h"
 #include "pxr/imaging/glf/simpleLightingContext.h"
 
 #include <maya/M3dView.h>
@@ -33,6 +34,7 @@
 #include <maya/MMatrix.h>
 #include <maya/MSelectionContext.h>
 
+#include <array>
 #include <ostream>
 
 
@@ -115,6 +117,40 @@ class px_vp20Utils
 };
 
 
+/// Simple RAII class to save uniform buffer bindings, to deal with a Maya
+/// issue.
+///
+/// XXX: When Maya is using OpenGL Core Profile as the rendering engine (in
+/// either compatibility or strict mode), batch renders like those done in the
+/// "Render View" window or through the ogsRender command do not properly track
+/// uniform buffer binding state. This was causing issues where the first batch
+/// render performed would look correct, but then all subsequent renders done
+/// in that Maya session would be completely black (no alpha), even if the
+/// frame contained only Maya-native geometry or if a new scene was
+/// created/opened.
+///
+/// To avoid this problem, this object can be used to save and restore Maya's
+/// uniform buffer bindings across Hydra/OpenGL calls. We try not to bog down
+/// performance by saving and restoring *all* GL_MAX_UNIFORM_BUFFER_BINDINGS
+/// possible bindings, so instead we only do just enough to avoid issues.
+/// Empirically, the problematic binding has been the material binding at
+/// index 4.
+class UBOBindingsSaver
+{
+    public:
+        static constexpr size_t UNIFORM_BINDINGS_TO_SAVE = 5u;
+
+        MAYAUSD_CORE_PUBLIC
+        UBOBindingsSaver();
+
+        MAYAUSD_CORE_PUBLIC
+        ~UBOBindingsSaver();
+
+    private:
+        std::array<GLint, UNIFORM_BINDINGS_TO_SAVE> _uniformBufferBindings;
+};
+
+
 PXR_NAMESPACE_CLOSE_SCOPE