Add support for GL_NV_read_depth

Change-Id: If2f96b4cc1c09cd28771740f09be5f84875033ab
Reviewed-on: https://swiftshader-review.googlesource.com/5091
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>

src/OpenGL/common/Image.cpp

diff --git a/src/OpenGL/common/Image.cpp b/src/OpenGL/common/Image.cpp
index 1abf389..6934787 100644
--- a/src/OpenGL/common/Image.cpp
+++ b/src/OpenGL/common/Image.cpp
@@ -526,6 +526,16 @@
 			default: UNREACHABLE(type);
 			}
 			break;
+		case GL_DEPTH_COMPONENT:
+			switch(type)
+			{
+			case GL_UNSIGNED_SHORT:        return sw::FORMAT_D16;
+			case GL_UNSIGNED_INT_24_8_OES: return sw::FORMAT_D24S8;
+			case GL_UNSIGNED_INT:          return sw::FORMAT_D32;
+			case GL_FLOAT:                 return sw::FORMAT_D32F;
+			default: UNREACHABLE(type);
+			}
+			break;
 		default:
 			UNREACHABLE(format);
 		}