diff --git a/Build/svencoop/renderer/shader/studio_shader.fsh b/Build/svencoop/renderer/shader/studio_shader.fsh
index 80938c7d..6702497e 100644
--- a/Build/svencoop/renderer/shader/studio_shader.fsh
+++ b/Build/svencoop/renderer/shader/studio_shader.fsh
@@ -508,12 +508,12 @@ vec3 R_StudioCelShade(vec3 v_color, vec3 normalWS, vec3 lightdirWS, float specul
 
 #endif
 
-#endif
+#endif    //defined(STUDIO_NF_CELSHADE_HAIR)
 
 	return v_color.xyz * litOrShadowColor + rimLightColor + rimDarkColor + specularColor;
-}
+}         //R_StudioCelShade
 
-#endif
+#endif  //defined(STUDIO_NF_CELSHADE)
 
 #if defined(STUDIO_NF_CELSHADE_FACE) && defined(STUDIO_DEBUG_ENABLED) 
 
diff --git a/Plugins/Renderer/exportfuncs.cpp b/Plugins/Renderer/exportfuncs.cpp
index 9c21126e..7be44349 100644
--- a/Plugins/Renderer/exportfuncs.cpp
+++ b/Plugins/Renderer/exportfuncs.cpp
@@ -93,10 +93,12 @@ void V_CalcRefdef(struct ref_params_s *pparams)
 	memcpy(&r_params, pparams, sizeof(struct ref_params_s));
 }
 
+#if 0
 void HUD_DrawTransparentTriangles(void)
 {
-	//gExportfuncs.HUD_DrawTransparentTriangles();
+	gExportfuncs.HUD_DrawTransparentTriangles();
 }
+#endif
 
 int HUD_Redraw(float time, int intermission)
 {
diff --git a/Plugins/Renderer/gl_draw.cpp b/Plugins/Renderer/gl_draw.cpp
index 9bf2b6f1..1fe5b8e0 100644
--- a/Plugins/Renderer/gl_draw.cpp
+++ b/Plugins/Renderer/gl_draw.cpp
@@ -414,6 +414,8 @@ void GL_UploadSubDataToVBODynamicDraw(GLuint VBO, size_t offset, size_t size, co
 
 void GL_UploadDataToEBOStaticDraw(GLuint EBO, size_t size, const void* data)
 {
+	//TODO: what if size == 0 ?
+
 	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
 	if (glBufferStorage)
 	{
diff --git a/Plugins/Renderer/gl_rmain.cpp b/Plugins/Renderer/gl_rmain.cpp
index 3285bd0c..2022296e 100644
--- a/Plugins/Renderer/gl_rmain.cpp
+++ b/Plugins/Renderer/gl_rmain.cpp
@@ -903,8 +903,8 @@ void R_DrawTransEntities(int onlyClientDraw)
 
 		glColorMask(1, 1, 1, 1);
 
-		GL_BlitFrameBufferToFrameBufferColorOnly(&s_BackBufferFBO, &s_BackBufferFBO2);
-		R_BlendOITBuffer(&s_BackBufferFBO2, &s_BackBufferFBO);
+		GL_BlitFrameBufferToFrameBufferColorOnly(GL_GetCurrentSceneFBO(), &s_BackBufferFBO2);
+		R_BlendOITBuffer(&s_BackBufferFBO2, GL_GetCurrentSceneFBO());
 
 		glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
 	}
@@ -1375,6 +1375,7 @@ void GL_FreeFrameBuffers(void)
 	GL_FreeFBO(&s_FinalBufferFBO);
 	GL_FreeFBO(&s_BackBufferFBO);
 	GL_FreeFBO(&s_BackBufferFBO2);
+	GL_FreeFBO(&s_BackBufferFBO3);
 	GL_FreeFBO(&s_GBufferFBO);
 	for (int i = 0; i < DOWNSAMPLE_BUFFERS; ++i)
 		GL_FreeFBO(&s_DownSampleFBO[i]);
@@ -1404,6 +1405,7 @@ void GL_GenerateFrameBuffers(void)
 	GL_GenFrameBuffer(&s_FinalBufferFBO);
 	GL_FrameBufferColorTexture(&s_FinalBufferFBO, GL_RGBA8);
 	GL_FrameBufferDepthTexture(&s_FinalBufferFBO, GL_DEPTH24_STENCIL8);
+	glDrawBuffer(GL_COLOR_ATTACHMENT0);
 
 	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
 	{
@@ -2081,6 +2083,7 @@ void R_RenderView_SvEngine(int viewIdx)
 	else
 	{
 		GL_BindFrameBuffer(&s_FinalBufferFBO);
+		GL_SetCurrentSceneFBO(NULL);
 	}
 
 	(*c_alias_polys) += r_studio_polys;
@@ -2835,6 +2838,22 @@ void R_AdjustScopeFOVForViewModel(float *fov)
 	}
 }
 
+void R_UseLegacyOpenGLMatrixForViewModel()
+{
+	glMatrixMode(GL_PROJECTION);
+	glLoadMatrixf(r_viewmodel_projection_matrix);
+	glMatrixMode(GL_MODELVIEW);
+	glLoadMatrixf(r_world_matrix);
+}
+
+void R_UseLegacyOpenGLMatrixForWorld()
+{
+	glMatrixMode(GL_PROJECTION);
+	glLoadMatrixf(r_projection_matrix);
+	glMatrixMode(GL_MODELVIEW);
+	glLoadMatrixf(r_world_matrix);
+}
+
 void R_UseProjMatrixForViewModel(void)
 {
 	scene_ubo_t SceneUBO;
@@ -3436,11 +3455,14 @@ void R_EndRenderOpaque(void)
 
 	if (R_IsGammaBlendEnabled())
 	{
-		R_GammaCorrection(GL_GetCurrentSceneFBO(), &s_BackBufferFBO3);
 		GL_BlitFrameBufferToFrameBufferDepthStencil(GL_GetCurrentSceneFBO(), &s_BackBufferFBO3);
+		R_GammaCorrection(GL_GetCurrentSceneFBO(), &s_BackBufferFBO3);
 		GL_SetCurrentSceneFBO(&s_BackBufferFBO3);
 		r_draw_gammablend = true;
 	}
+
+	//For backward compatibility, some Mods may use Legacy OpenGL 1.x Matrix
+	R_UseLegacyOpenGLMatrixForWorld();
 }
 
 void ClientDLL_DrawNormalTriangles(void)
diff --git a/Plugins/Renderer/gl_shader.h b/Plugins/Renderer/gl_shader.h
index cc2522c1..fed0df27 100644
--- a/Plugins/Renderer/gl_shader.h
+++ b/Plugins/Renderer/gl_shader.h
@@ -52,5 +52,5 @@ void R_SaveProgramStatesCaches(const char *filename, const std::vector<program_s
 
 #define SHADER_DEFINE(name) name##_program_t name;
 
-#define SHADER_UNIFORM(name, loc, locstring) name##.loc = glGetUniformLocationARB(name.program, locstring);
-#define SHADER_ATTRIB(name, loc, locstring) name##.loc = glGetAttribLocationARB(name.program, locstring);
+#define SHADER_UNIFORM(name, loc, locstring) name##.loc = glGetUniformLocation(name.program, locstring);
+#define SHADER_ATTRIB(name, loc, locstring) name##.loc = glGetAttribLocation(name.program, locstring);
diff --git a/Plugins/Renderer/gl_sprite.cpp b/Plugins/Renderer/gl_sprite.cpp
index 342244c6..90164f2a 100644
--- a/Plugins/Renderer/gl_sprite.cpp
+++ b/Plugins/Renderer/gl_sprite.cpp
@@ -177,6 +177,7 @@ void R_UseLegacySpriteProgram(program_state_t state, legacysprite_program_t *pro
 		auto def = defs.str();
 
 		prog.program = R_CompileShaderFileEx("renderer\\shader\\legacysprite_shader.vsh", "renderer\\shader\\legacysprite_shader.fsh", def.c_str(), def.c_str(), NULL);
+
 		if (prog.program)
 		{