OGL: Work around slowdown of glMapBufferRange with SSBO on NVIDIA drivers

Using glMapBufferRange to read back the contents of the SSBO is extremely
slow on NVIDIA drivers. This is more noticeable at higher internal
resolutions. Using glGetBufferSubData instead does not seem to exhibit
this slowdown.

1 files changed, 18 insertions, 4 deletions

diff --git a/Source/Core/VideoBackends/OGL/BoundingBox.cpp b/Source/Core/VideoBackends/OGL/BoundingBox.cpp
index b8e424f639..c4c0012ddc 100644
--- a/Source/Core/VideoBackends/OGL/BoundingBox.cpp
+++ b/Source/Core/VideoBackends/OGL/BoundingBox.cpp
@@ -6,6 +6,7 @@
 
 #include "VideoBackends/OGL/BoundingBox.h"
 
+#include "VideoCommon/DriverDetails.h"
 #include "VideoCommon/VideoConfig.h"
 
 static GLuint s_bbox_buffer_id;
@@ -42,12 +43,25 @@ int BoundingBox::Get(int index)
 {
 	int data = 0;
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, s_bbox_buffer_id);
-	void* ptr = glMapBufferRange(GL_SHADER_STORAGE_BUFFER, index * sizeof(int), sizeof(int), GL_MAP_READ_BIT);
-	if (ptr)
+
+	if (!DriverDetails::HasBug(DriverDetails::BUG_SLOWGETBUFFERSUBDATA))
+	{
+		// Using glMapBufferRange to read back the contents of the SSBO is extremely slow
+		// on nVidia drivers. This is more noticeable at higher internal resolutions.
+		// Using glGetBufferSubData instead does not seem to exhibit this slowdown.
+		glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, index * sizeof(int), sizeof(int), &data);
+	}
+	else
 	{
-		data = *(int*)ptr;
-		glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
+		// Using glMapBufferRange is faster on AMD cards by a measurable margin.
+		void* ptr = glMapBufferRange(GL_SHADER_STORAGE_BUFFER, index * sizeof(int), sizeof(int), GL_MAP_READ_BIT);
+		if (ptr)
+		{
+			memcpy(&data, ptr, sizeof(int));
+			glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
+		}
 	}
+
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
 	return data;
 }