From ae859934cafffb1050b3230002df324c5a02e859 Mon Sep 17 00:00:00 2001
From: Hans-Kristian Arntzen <hans-kristian.arntzen@arm.com>
Date: Thu, 23 Aug 2018 15:37:09 +0200
Subject: [PATCH] Use GL_NV_gpu_shader5 as a fallback for
 AMD_gpu_shader_half_float.

---
 .../shaders/desktop-only/frag/fp16.desktop.frag |  6 ++++++
 .../shaders/desktop-only/frag/fp16.desktop.frag |  6 ++++++
 spirv_glsl.cpp                                  | 17 ++++++++++++++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/reference/opt/shaders/desktop-only/frag/fp16.desktop.frag b/reference/opt/shaders/desktop-only/frag/fp16.desktop.frag
index 1761424e..4586a8ec 100644
--- a/reference/opt/shaders/desktop-only/frag/fp16.desktop.frag
+++ b/reference/opt/shaders/desktop-only/frag/fp16.desktop.frag
@@ -1,5 +1,11 @@
 #version 450
+#if defined(GL_AMD_gpu_shader_half_float)
 #extension GL_AMD_gpu_shader_half_float : require
+#elif defined(GL_NV_gpu_shader5)
+#extension GL_NV_gpu_shader5 : require
+#else
+#error No extension available for FP16.
+#endif
 
 layout(location = 3) in f16vec4 v4;
 
diff --git a/reference/shaders/desktop-only/frag/fp16.desktop.frag b/reference/shaders/desktop-only/frag/fp16.desktop.frag
index 0c5203a1..e1fc045c 100644
--- a/reference/shaders/desktop-only/frag/fp16.desktop.frag
+++ b/reference/shaders/desktop-only/frag/fp16.desktop.frag
@@ -1,5 +1,11 @@
 #version 450
+#if defined(GL_AMD_gpu_shader_half_float)
 #extension GL_AMD_gpu_shader_half_float : require
+#elif defined(GL_NV_gpu_shader5)
+#extension GL_NV_gpu_shader5 : require
+#else
+#error No extension available for FP16.
+#endif
 
 struct ResType
 {
diff --git a/spirv_glsl.cpp b/spirv_glsl.cpp
index 542ec733..78cce962 100644
--- a/spirv_glsl.cpp
+++ b/spirv_glsl.cpp
@@ -479,7 +479,22 @@ void CompilerGLSL::emit_header()
 	}
 
 	for (auto &ext : forced_extensions)
-		statement("#extension ", ext, " : require");
+	{
+		if (ext == "GL_AMD_gpu_shader_half_float" && !options.vulkan_semantics)
+		{
+			// Special case, this extension has a potential fallback to another vendor extension in normal GLSL.
+			// GL_AMD_gpu_shader_half_float is a superset, so try that first.
+			statement("#if defined(GL_AMD_gpu_shader_half_float)");
+			statement("#extension GL_AMD_gpu_shader_half_float : require");
+			statement("#elif defined(GL_NV_gpu_shader5)");
+			statement("#extension GL_NV_gpu_shader5 : require");
+			statement("#else");
+			statement("#error No extension available for FP16.");
+			statement("#endif");
+		}
+		else
+			statement("#extension ", ext, " : require");
+	}
 
 	for (auto &header : header_lines)
 		statement(header);