Enables stereo rendering with OpenGL ES 3.1 + AEP.

If the host device supports GLES 3.1 and AEP we can have stereo rendering.
Just need to make sure to grab the correct function pointer that GL_EXT_geometry_shader provides, and enable AEP in the shaders.

We can't just check if AEP is in the extension list for support because Qualcomm has failed once more.
With the Nexus 6 it reports support for AEP but doesn't support OpenGL ES 3.1, which is an impossible combination.
From reports on their forum it seems that attempting to use any AEP things results in nothing happening, seems like a stub implementation.

Source/Core/VideoBackends/OGL/GLExtensions/GLExtensions.cpp

@@ -1576,6 +1576,9 @@ const GLFunc gl_function_array[] =
 	// ARB_buffer_storage
 	GLFUNC_REQUIRES(glBufferStorage,         "GL_ARB_buffer_storage"),
 	GLFUNC_REQUIRES(glNamedBufferStorageEXT, "GL_ARB_buffer_storage GL_EXT_direct_state_access"),
+
+	// EXT_geometry_shader
+	GLFUNC_SUFFIX(glFramebufferTexture, EXT, "GL_EXT_geometry_shader !VERSION_3_2"),
 };
 
 namespace GLExtensions

Source/Core/VideoBackends/OGL/ProgramShaderCache.cpp

@@ -505,6 +505,7 @@ void ProgramShaderCache::Shutdown()
 void ProgramShaderCache::CreateHeader()
 {
 	GLSL_VERSION v = g_ogl_config.eSupportedGLSLVersion;
+
 	snprintf(s_glsl_header, sizeof(s_glsl_header),
 		"%s\n"
 		"%s\n" // ubo
@@ -515,6 +516,7 @@ void ProgramShaderCache::CreateHeader()
 		"%s\n" // Sampler binding
 		"%s\n" // storage buffer
 		"%s\n" // shader5
+		"%s\n" // AEP
 
 		// Precision defines for GLSL ES
 		"%s\n"
@@ -549,6 +551,7 @@ void ProgramShaderCache::CreateHeader()
 		, g_ActiveConfig.backend_info.bSupportsBindingLayout ? "#define SAMPLER_BINDING(x) layout(binding = x)" : "#define SAMPLER_BINDING(x)"
 		, g_ActiveConfig.backend_info.bSupportsBBox ? "#extension GL_ARB_shader_storage_buffer_object : enable" : ""
 		, g_ActiveConfig.backend_info.bSupportsGSInstancing ? "#extension GL_ARB_gpu_shader5 : enable" : ""
+		, g_ogl_config.bSupportsAEP ? "#extension GL_ANDROID_extension_pack_es31a : enable" : ""
 
 		, v>=GLSLES_300 ? "precision highp float;" : ""
 		, v>=GLSLES_300 ? "precision highp int;" : ""

Source/Core/VideoBackends/OGL/Render.cpp

@@ -497,15 +497,17 @@ Renderer::Renderer()
 		if (strstr(g_ogl_config.glsl_version, "3.0"))
 		{
 			g_ogl_config.eSupportedGLSLVersion = GLSLES_300;
+			g_ogl_config.bSupportsAEP = false;
+			g_Config.backend_info.bSupportsStereoscopy = false;
 		}
 		else
 		{
 			g_ogl_config.eSupportedGLSLVersion = GLSLES_310;
+			g_ogl_config.bSupportsAEP = GLExtensions::Supports("GL_ANDROID_extension_pack_es31a");
 			g_Config.backend_info.bSupportsBindingLayout = true;
 			g_Config.backend_info.bSupportsEarlyZ = true;
+			g_Config.backend_info.bSupportsStereoscopy = g_ogl_config.bSupportsAEP;
 		}
-		// TODO: OpenGL ES 3.1 provides the necessary features as extensions.
-		g_Config.backend_info.bSupportsStereoscopy = false;
 	}
 	else
 	{
@@ -532,6 +534,9 @@ Renderer::Renderer()
 		{
 			g_ogl_config.eSupportedGLSLVersion = GLSL_150;
 		}
+
+		// Desktop OpenGL can't have the Android Extension Pack
+		g_ogl_config.bSupportsAEP = false;
 	}
 
 	if (GLExtensions::Supports("GL_KHR_debug"))

Source/Core/VideoBackends/OGL/Render.h

@@ -30,6 +30,7 @@ struct VideoConfig
 	GLSL_VERSION eSupportedGLSLVersion;
 	bool bSupportOGL31;
 	bool bSupportViewportFloat;
+	bool bSupportsAEP;
 
 	const char* gl_vendor;
 	const char* gl_renderer;