From 02f77bbf12981abe376b2d5987684224a50ae4b2 Mon Sep 17 00:00:00 2001
From: Tim Foley <tfoley@nvidia.com>
Date: Wed, 12 Jul 2017 14:21:52 -0700
Subject: Add ability for intrinsics to require GLSL extensions

When cross-compiling, we need to detect when an intrinsic is used that required non-default GLSL capabilities and emit an appropriate `#extension ... : require` line.

I'm handling this by attaching a custom modifier to declarations that require an extension in order to be callable.
---
 source/slang/emit.cpp | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

(limited to 'source/slang/emit.cpp')

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index f5b4a8b56..6905a8a76 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -52,6 +52,10 @@ struct SharedEmitContext
     ProgramSyntaxNode*  program;
 
     bool                needHackSamplerForTexelFetch = false;
+
+    // Record the GLSL extnsions we have already emitted a `#extension` for
+    HashSet<String> glslExtensionsRequired;
+    StringBuilder glslExtensionRequireLines;
 };
 
 struct EmitContext
@@ -1594,6 +1598,19 @@ struct EmitVisitor
         }
     }
 
+    void requireGLSLExtension(String const& name)
+    {
+        if (context->shared->glslExtensionsRequired.Contains(name))
+            return;
+
+        StringBuilder& sb = context->shared->glslExtensionRequireLines;
+
+        sb.append("#extension ");
+        sb.append(name);
+        sb.append(" : require\n");
+
+        context->shared->glslExtensionsRequired.Add(name);
+    }
 
     void visitInvokeExpressionSyntaxNode(
         RefPtr<InvokeExpressionSyntaxNode>  callExpr,
@@ -1708,6 +1725,17 @@ struct EmitVisitor
             }
             else if(auto targetIntrinsicModifier = findTargetIntrinsicModifier(funcDecl))
             {
+                if (context->shared->target == CodeGenTarget::GLSL)
+                {
+                    // Does this intrinsic requie a particular GLSL extension that wouldn't be available by default?
+                    if (auto requiredGLSLExtensionModifier = funcDecl->FindModifier<RequiredGLSLExtensionModifier>())
+                    {
+                        // If so, we had better request the extension.
+                        requireGLSLExtension(requiredGLSLExtensionModifier->extensionNameToken.Content);
+                    }
+                }
+
+
                 if(targetIntrinsicModifier->definitionToken.Type != TokenType::Unknown)
                 {
                     auto name = getStringOrIdentifierTokenValue(targetIntrinsicModifier->definitionToken);
@@ -3550,6 +3578,8 @@ String emitEntryPoint(
     StringBuilder finalResultBuilder;
     finalResultBuilder << prefix;
 
+    finalResultBuilder << sharedContext.glslExtensionRequireLines.ProduceString();
+
     if (sharedContext.needHackSamplerForTexelFetch)
     {
         finalResultBuilder << "layout(set = 0, binding = 0) uniform sampler SLANG_hack_samplerForTexelFetch;\n";
-- 
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