Use Color3::srgbToLinear in Metal background color conversion

Author: aabhinavvvvvvv

source/MaterialXView/RenderPipelineMetal.mm

@@ -472,17 +472,14 @@
     // background color must be converted to linear before being set as the clear color.
     // On OpenGL (Windows), the background is stored directly in a non-linear framebuffer
     // and no conversion is needed.
-    auto srgbToLinear = [](float srgb) -> float {
-        if (srgb <= 0.04045f)
-            return srgb / 12.92f;
-        else
-            return std::pow((srgb + 0.055f) / 1.055f, 2.4f);
-    };
+    mx::Color3 bgLinear = mx::Color3(_viewer->m_background[0],
+                                     _viewer->m_background[1],
+                                     _viewer->m_background[2]).srgbToLinear();
 
     [renderpassDesc.colorAttachments[0] setClearColor:MTLClearColorMake(
-                                        srgbToLinear(_viewer->m_background[0]),
-                                        srgbToLinear(_viewer->m_background[1]),
-                                        srgbToLinear(_viewer->m_background[2]),
+                                        bgLinear[0],
+                                        bgLinear[1],
+                                        bgLinear[2],
                                         _viewer->m_background[3])];
     [renderpassDesc.colorAttachments[0] setLoadAction:MTLLoadActionClear];
     [renderpassDesc.colorAttachments[0] setStoreAction:MTLStoreActionStore];