Load winsys and gl dynamically in the windows plugin

The dynamic builds (-opengl dynamic) are now functional on Windows.

In such a build no components in Qt link to any OpenGL libraries directly
and qmake will not automatically add any such libraries to the
applications' makefiles. Instead, the libraries are chosen and loaded
during runtime and applications are expected to use QOpenGLFunctions
instead of direct OpenGLfunction calls.

Set the environment variable QT_OPENGL to desktop or angle to skip testing
and force the given implementation. The application attributes (AA_UseOpenGLES
and such) are also taken into account.

The testing logic is same as before: We try to load opengl32 and
resolve a shader related function. If this fails, ANGLE is chosen. This
allows utilizing full desktop OpenGL on systems that have proper drivers,
while a transparent fallback to ANGLE will be done automatically for
systems that don't. The latter includes also remote desktop connections.

Software rendering via Mesa llvmpipe is supported too. The fallback is
automatic on systems where the desktop test fails and ANGLE fails to load
or initialize (e.g. due to missing libs like d3dcompiler), as long as a
suitable patched build of Mesa is available.

[ChangeLog][QtGui] Dynamic OpenGL implementation loading is now supported
on Windows. This requires Qt to be configured with -opengl dynamic.

Task-number: QTBUG-36483
Change-Id: Ie8bb25a6d55b3a1609b00150aeccd909aec27313
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

1 files changed, 146 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowsopengltester.cpp b/src/plugins/platforms/windows/qwindowsopengltester.cpp
new file mode 100644
index 0000000000..9ee62e6d56
--- /dev/null
+++ b/src/plugins/platforms/windows/qwindowsopengltester.cpp
@@ -0,0 +1,146 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qwindowsopengltester.h"
+#include "qt_windows.h"
+#include "qwindowscontext.h"
+
+QT_BEGIN_NAMESPACE
+
+bool QWindowsOpenGLTester::testDesktopGL()
+{
+    HMODULE lib = 0;
+    HWND wnd = 0;
+    HDC dc = 0;
+    HGLRC context = 0;
+    LPCTSTR className = L"qtopengltest";
+
+    HGLRC (WINAPI * CreateContext)(HDC dc) = 0;
+    BOOL (WINAPI * DeleteContext)(HGLRC context) = 0;
+    BOOL (WINAPI * MakeCurrent)(HDC dc, HGLRC context) = 0;
+    PROC (WINAPI * WGL_GetProcAddress)(LPCSTR name) = 0;
+
+    bool result = false;
+
+    // Test #1: Load opengl32.dll and try to resolve an OpenGL 2 function.
+    // This will typically fail on systems that do not have a real OpenGL driver.
+    lib = LoadLibraryA("opengl32.dll");
+    if (lib) {
+        CreateContext = reinterpret_cast<HGLRC (WINAPI *)(HDC)>(::GetProcAddress(lib, "wglCreateContext"));
+        if (!CreateContext)
+            goto cleanup;
+        DeleteContext = reinterpret_cast<BOOL (WINAPI *)(HGLRC)>(::GetProcAddress(lib, "wglDeleteContext"));
+        if (!DeleteContext)
+            goto cleanup;
+        MakeCurrent = reinterpret_cast<BOOL (WINAPI *)(HDC, HGLRC)>(::GetProcAddress(lib, "wglMakeCurrent"));
+        if (!MakeCurrent)
+            goto cleanup;
+        WGL_GetProcAddress = reinterpret_cast<PROC (WINAPI *)(LPCSTR)>(::GetProcAddress(lib, "wglGetProcAddress"));
+        if (!WGL_GetProcAddress)
+            goto cleanup;
+
+        WNDCLASS wclass;
+        wclass.cbClsExtra = 0;
+        wclass.cbWndExtra = 0;
+        wclass.hInstance = (HINSTANCE) GetModuleHandle(0);
+        wclass.hIcon = 0;
+        wclass.hCursor = 0;
+        wclass.hbrBackground = (HBRUSH) (COLOR_BACKGROUND);
+        wclass.lpszMenuName = 0;
+        wclass.lpfnWndProc = DefWindowProc;
+        wclass.lpszClassName = className;
+        wclass.style = CS_OWNDC;
+        if (!RegisterClass(&wclass))
+            goto cleanup;
+        wnd = CreateWindow(className, L"qtopenglproxytest", WS_OVERLAPPED,
+                           0, 0, 640, 480, 0, 0, wclass.hInstance, 0);
+        if (!wnd)
+            goto cleanup;
+        dc = GetDC(wnd);
+        if (!dc)
+            goto cleanup;
+
+        PIXELFORMATDESCRIPTOR pfd;
+        memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
+        pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
+        pfd.nVersion = 1;
+        pfd.dwFlags = PFD_SUPPORT_OPENGL | PFD_DRAW_TO_WINDOW | PFD_GENERIC_FORMAT;
+        pfd.iPixelType = PFD_TYPE_RGBA;
+        // Use the GDI functions. Under the hood this will call the wgl variants in opengl32.dll.
+        int pixelFormat = ChoosePixelFormat(dc, &pfd);
+        if (!pixelFormat)
+            goto cleanup;
+        if (!SetPixelFormat(dc, pixelFormat, &pfd))
+            goto cleanup;
+        context = CreateContext(dc);
+        if (!context)
+            goto cleanup;
+        if (!MakeCurrent(dc, context))
+            goto cleanup;
+
+        // Now that there is finally a context current, try doing something useful.
+        if (WGL_GetProcAddress("glCreateShader")) {
+            result = true;
+            qCDebug(lcQpaGl, "OpenGL 2.0 entry points available");
+        } else {
+            qCDebug(lcQpaGl, "OpenGL 2.0 entry points not found");
+        }
+    } else {
+        qCDebug(lcQpaGl, "Failed to load opengl32.dll");
+    }
+
+cleanup:
+    if (MakeCurrent)
+        MakeCurrent(0, 0);
+    if (context)
+        DeleteContext(context);
+    if (dc && wnd)
+        ReleaseDC(wnd, dc);
+    if (wnd) {
+        DestroyWindow(wnd);
+        UnregisterClass(className, GetModuleHandle(0));
+    }
+    // No FreeLibrary. Some implementations, Mesa in particular, deadlock when trying to unload.
+
+    return result;
+}
+
+QT_END_NAMESPACE