3 files changed, 17 insertions, 3 deletions
diff --git a/indra/llwindow/llopenglview-objc.mm b/indra/llwindow/llopenglview-objc.mm
index fd20f2ad15..8d064ec86c 100644
--- a/indra/llwindow/llopenglview-objc.mm
+++ b/indra/llwindow/llopenglview-objc.mm
@@ -141,7 +141,12 @@ attributedStringInfo getSegments(NSAttributedString *str)
     CGLError the_err = CGLQueryRendererInfo (CGDisplayIDToOpenGLDisplayMask(kCGDirectMainDisplay), &info, &num_renderers);
     if(0 == the_err)
     {
-        CGLDescribeRenderer (info, 0, kCGLRPTextureMemoryMegabytes, &vram_megabytes);
+        // The name, uses, and other platform definitions of gGLManager.mVRAM suggest that this is supposed to be total vram in MB,
+        // rather than, say, just the texture memory. The two exceptions are:
+        // 1. LLAppViewer::getViewerInfo() puts the value in a field labeled "TEXTURE_MEMORY"
+        // 2. For years, this present function used kCGLRPTextureMemoryMegabytes
+        // Now we use kCGLRPVideoMemoryMegabytes to bring it in line with everything else (except thatone label).
+        CGLDescribeRenderer (info, 0, kCGLRPVideoMemoryMegabytes, &vram_megabytes);
         CGLDestroyRendererInfo (info);
     }
     else
diff --git a/indra/llwindow/llwindowmacosx.cpp b/indra/llwindow/llwindowmacosx.cpp
index bc4f07941b..4bcb9b3aef 100644
--- a/indra/llwindow/llwindowmacosx.cpp
+++ b/indra/llwindow/llwindowmacosx.cpp
@@ -1222,6 +1222,16 @@ F32 LLWindowMacOSX::getPixelAspectRatio()
 	return 1.f;
 }
 
+U32 LLWindowMacOSX::getAvailableVRAMMegabytes() {
+    // MTL (and MoltenVK) has some additional gpu data, such as recommendedMaxWorkingSetSize and currentAllocatedSize.
+    // But these are not available for OpenGL and/or our current mimimum OS version.
+    // So we will estimate.
+    static const U32 mb = 1024*1024;
+    // We're asked for total available gpu memory, but we only have allocation info on texture usage. So estimate by doubling that.
+    static const U32 total_factor = 2; // estimated total/textures
+    return gGLManager.mVRAM - (LLImageGL::getTextureBytesAllocated() * total_factor/mb);
+}
+
 //static SInt32 oldWindowLevel;
 
 // MBW -- XXX -- There's got to be a better way than this.  Find it, please...
diff --git a/indra/llwindow/llwindowmacosx.h b/indra/llwindow/llwindowmacosx.h
index 309d1377ea..0f316f1ddf 100644
--- a/indra/llwindow/llwindowmacosx.h
+++ b/indra/llwindow/llwindowmacosx.h
@@ -101,8 +101,7 @@ public:
 	void setNativeAspectRatio(F32 ratio) override { mOverrideAspectRatio = ratio; }
 
 	// query VRAM usage
-	// FIXME FIXME
-	virtual U32 getAvailableVRAMMegabytes() override { return 0; }
+    /*virtual*/ U32 getAvailableVRAMMegabytes() override;
 
 	void beforeDialog() override;
 	void afterDialog() override;