From: Mikko Rasa <tdb@tdb.fi>
Date: Tue, 20 Sep 2016 23:37:53 +0000 (+0300)
Subject: Work around a calling convention mismatch between MinGW and VC++
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=39628c9575865e0be5ae44875989c01ac151ccd2;p=libs%2Fvr.git

Work around a calling convention mismatch between MinGW and VC++
---

diff --git a/source/openvr/openvrdevice.cpp b/source/openvr/openvrdevice.cpp
index 466a71f..f6f0bf1 100644
--- a/source/openvr/openvrdevice.cpp
+++ b/source/openvr/openvrdevice.cpp
@@ -50,8 +50,22 @@ OpenVRDevice::~OpenVRDevice()
 void OpenVRDevice::configure_view(StereoView &view) const
 {
 	vr::IVRSystem *vr_sys = vr::VRSystem();
+
+#if defined(__GNUC__) && defined(_WIN32)
+	/* Visual C++ passes the return value address as first stack parameter and
+	the this pointer in ecx.  MinGW does the other way around.  This trick
+	forces the function signature to match at machine code level. */
+	typedef void (vr::IVRSystem::*FuncPtr)(vr::HmdMatrix34_t *, vr::EVREye);
+	FuncPtr get_eye_to_head_transform = reinterpret_cast<FuncPtr>(&vr::IVRSystem::GetEyeToHeadTransform);
+
+	vr::HmdMatrix34_t left, right;
+	(vr_sys->*get_eye_to_head_transform)(&left, vr::Eye_Left);
+	(vr_sys->*get_eye_to_head_transform)(&right, vr::Eye_Right);
+#else
 	vr::HmdMatrix34_t left = vr_sys->GetEyeToHeadTransform(vr::Eye_Left);
 	vr::HmdMatrix34_t right = vr_sys->GetEyeToHeadTransform(vr::Eye_Right);
+#endif
+	
 	view.set_eye_matrices(convert_matrix(left), convert_matrix(right));
 }