Add an option in ANGLE shader translator to initialize gl_Position to vec4(0.0, 0.0, 0.0, 1.0).
This is to work around driver bugs where shader compile or program link would fail incorrectly if gl_Position is not set in vertex shader.
At the moment at least Linux NVIDIA driver has this bug.
ANGLEBUG=472
R=alokp@chromium.org, kbr@chromium.org
Review URL: https://codereview.appspot.com/13509043
diff --git a/src/compiler/InitializeGLPosition.cpp b/src/compiler/InitializeGLPosition.cpp
new file mode 100644
index 0000000..e0193e3
--- /dev/null
+++ b/src/compiler/InitializeGLPosition.cpp
@@ -0,0 +1,61 @@
+//
+// Copyright (c) 2002-2013 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+
+#include "compiler/InitializeGLPosition.h"
+#include "compiler/debug.h"
+
+bool InitializeGLPosition::visitAggregate(Visit visit, TIntermAggregate* node)
+{
+ bool visitChildren = !mCodeInserted;
+ switch (node->getOp())
+ {
+ case EOpSequence: break;
+ case EOpFunction:
+ {
+ // Function definition.
+ ASSERT(visit == PreVisit);
+ if (node->getName() == "main(")
+ {
+ TIntermSequence &sequence = node->getSequence();
+ ASSERT((sequence.size() == 1) || (sequence.size() == 2));
+ TIntermAggregate *body = NULL;
+ if (sequence.size() == 1)
+ {
+ body = new TIntermAggregate(EOpSequence);
+ sequence.push_back(body);
+ }
+ else
+ {
+ body = sequence[1]->getAsAggregate();
+ }
+ ASSERT(body);
+ insertCode(body->getSequence());
+ mCodeInserted = true;
+ }
+ break;
+ }
+ default: visitChildren = false; break;
+ }
+ return visitChildren;
+}
+
+void InitializeGLPosition::insertCode(TIntermSequence& sequence)
+{
+ TIntermBinary *binary = new TIntermBinary(EOpAssign);
+ sequence.insert(sequence.begin(), binary);
+
+ TIntermSymbol *left = new TIntermSymbol(
+ 0, "gl_Position", TType(EbtFloat, EbpUndefined, EvqPosition, 4));
+ binary->setLeft(left);
+
+ ConstantUnion *u = new ConstantUnion[4];
+ for (int ii = 0; ii < 3; ++ii)
+ u[ii].setFConst(0.0f);
+ u[3].setFConst(1.0f);
+ TIntermConstantUnion *right = new TIntermConstantUnion(
+ u, TType(EbtFloat, EbpUndefined, EvqConst, 4));
+ binary->setRight(right);
+}