use UBOBindingsSaver when rendering in Pixar's batch renderer

With UBOBindingsSaver now available from px_vp20/utils, this change uses that
class to wrap the Hydra Execute() call made during rendering.

lib/render/pxrUsdMayaGL/batchRenderer.cpp

@@ -22,8 +22,8 @@
 #include "./debugCodes.h"
 #include "./userData.h"
 
-#include "../px_vp20/utils.h"
-#include "../px_vp20/utils_legacy.h"
+#include "mayaUsd/render/px_vp20/utils.h"
+#include "mayaUsd/render/px_vp20/utils_legacy.h"
 
 #include "pxr/base/gf/matrix4d.h"
 #include "pxr/base/gf/vec2i.h"
@@ -1294,27 +1294,7 @@ UsdMayaGLBatchRenderer::_Render(
                  GL_DEPTH_BUFFER_BIT |
                  GL_VIEWPORT_BIT);
 
-    // 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.
-    static constexpr size_t _UNIFORM_BINDINGS_TO_SAVE = 5u;
-    std::vector<GLint> uniformBufferBindings(_UNIFORM_BINDINGS_TO_SAVE, 0);
-    for (size_t i = 0u; i < uniformBufferBindings.size(); ++i) {
-        glGetIntegeri_v(GL_UNIFORM_BUFFER_BINDING,
-                        (GLuint)i,
-                        &uniformBufferBindings[i]);
-    }
+    UBOBindingsSaver bindingsSaver;
 
     // hydra orients all geometry during topological processing so that
     // front faces have ccw winding. We disable culling because culling
@@ -1374,13 +1354,6 @@ UsdMayaGLBatchRenderer::_Render(
 
     glDisable(GL_FRAMEBUFFER_SRGB_EXT);
 
-    // XXX: Restore Maya's uniform buffer binding state. See above for details.
-    for (size_t i = 0u; i < uniformBufferBindings.size(); ++i) {
-        glBindBufferBase(GL_UNIFORM_BUFFER,
-                         (GLuint)i,
-                         uniformBufferBindings[i]);
-    }
-
     glPopAttrib(); // GL_LIGHTING_BIT | GL_ENABLE_BIT | GL_POLYGON_BIT |
                    // GL_DEPTH_BUFFER_BIT | GL_VIEWPORT_BIT
 }