Availability guard for Metal

Author: dnfield

impeller/renderer/backend/metal/formats_mtl.h

@@ -52,6 +52,11 @@ constexpr PixelFormat FromMTLPixelFormat(MTLPixelFormat format) {
   return PixelFormat::kUnknown;
 }
 
+/// Safe accessor for MTLPixelFormatDepth24Unorm_Stencil8.
+/// Returns PixelFormat::kUnknown if MTLPixelFormatDepth24Unorm_Stencil8 isn't
+/// supported.
+MTLPixelFormat SafeMTLPixelFormatDepth24Unorm_Stencil8();
+
 /// Safe accessor for MTLPixelFormatBGR10_XR_sRGB.
 /// Returns PixelFormat::kUnknown if MTLPixelFormatBGR10_XR_sRGB isn't
 /// supported.
@@ -90,7 +95,7 @@ constexpr MTLPixelFormat ToMTLPixelFormat(PixelFormat format) {
     case PixelFormat::kS8UInt:
       return MTLPixelFormatStencil8;
     case PixelFormat::kD24UnormS8Uint:
-      return MTLPixelFormatDepth24Unorm_Stencil8;
+      return SafeMTLPixelFormatDepth24Unorm_Stencil8();
     case PixelFormat::kD32FloatS8UInt:
       return MTLPixelFormatDepth32Float_Stencil8;
     case PixelFormat::kB10G10R10XRSRGB:

impeller/renderer/backend/metal/formats_mtl.mm

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "impeller/renderer/backend/metal/formats_mtl.h"
+#include <Metal/Metal.h>
 
 #include <memory>
 
@@ -109,6 +110,13 @@
   return mtl_desc;
 }
 
+MTLPixelFormat SafeMTLPixelFormatDepth24Unorm_Stencil8() {
+  if (@available(macOS 10.11, *)) {
+    return MTLPixelFormatDepth24Unorm_Stencil8;
+  }
+  return MTLPixelFormatInvalid;
+}
+
 MTLPixelFormat SafeMTLPixelFormatBGR10_XR_sRGB() {
   if (@available(iOS 11, macOS 11.0, *)) {
     return MTLPixelFormatBGR10_XR_sRGB;