Add Linux and AMD support to the OpenCL filter example

Change-Id: I1ea91f93677c53322c3867db6069e4362c58cebd
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>

examples/multimedia/video/qmlvideofilter_opencl/README

@@ -1,18 +1,18 @@
-This example performs some simple OpenCL operations on camera or video input which
-is assumed to be provided in RGB format. The OpenCL operation is done on an
-OpenGL texture using CL-GL interop, without any further readbacks or copies
+This example performs some simple OpenCL operations on camera or video input
+which is assumed to be provided in RGB format. The OpenCL operation is done on
+an OpenGL texture using CL-GL interop, without any further readbacks or copies
 (except for the initial texture upload, when necessary).
 
-Currently only OS X and Windows with desktop OpenGL (opengl32.dll) are supported.
-On Windows you may need to edit testplugin.pro to specify the location of the OpenCL
-headers and libraries.
+Currently OS X, Windows with real OpenGL (opengl32.dll) and Linux (GLX only) are
+supported. Note that an OpenCL implementation with GPU support is required. The
+platform and device selection logic supports NVIDIA, AMD and Intel. Porting to
+other platforms is probably simple, see clCreateContextFromType.
 
-Note that an OpenCL implementation with GPU support is required.
-The platform and device selection logic supports NVIDIA and Intel.
-Porting to other platforms is probably simple, see clCreateContextFromType.
-Note however that YUV formats, that are commonly used also for camera input
-on some platforms, are not supported in this example.
+On Windows you may need to edit testplugin.pro to specify the location of the
+OpenCL headers and libraries.
+
+YUV formats are not supported in this example. This is probably not an issue an
+OS X and Windows, but will most likely disable the example on Linux.
 
 Pass the name of a video file to perform video playback or launch without
 arguments to use the camera.
-

examples/multimedia/video/qmlvideofilter_opencl/main.cpp

@@ -46,6 +46,10 @@
 #include <CL/opencl.h>
 #endif
 
+#ifdef Q_OS_LINUX
+#include <QtPlatformHeaders/QGLXNativeContext>
+#endif
+
 #include "rgbframehelper.h"
 
 static const char *openclSrc =
@@ -119,10 +123,17 @@ CLFilterRunnable::CLFilterRunnable(CLFilter *filter) :
 
     // Set up OpenCL.
     QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
-    cl_int err;
     cl_uint n;
-    if (clGetPlatformIDs(0, 0, &n) != CL_SUCCESS) {
-        qWarning("Failed to get platform ID count");
+    cl_int err = clGetPlatformIDs(0, 0, &n);
+    if (err != CL_SUCCESS) {
+        qWarning("Failed to get platform ID count (error %d)", err);
+        if (err == -1001) {
+            qDebug("Could not find OpenCL implementation. ICD missing?"
+#ifdef Q_OS_LINUX
+                   " Check /etc/OpenCL/vendors."
+#endif
+                );
+        }
         return;
     }
     if (n == 0) {
@@ -140,6 +151,7 @@ CLFilterRunnable::CLFilterRunnable(CLFilter *filter) :
     qDebug("GL_VENDOR: %s", vendor);
     const bool isNV = vendor && strstr(vendor, "NVIDIA");
     const bool isIntel = vendor && strstr(vendor, "Intel");
+    const bool isAMD = vendor && strstr(vendor, "ATI");
     qDebug("Found %u OpenCL platforms:", n);
     for (cl_uint i = 0; i < n; ++i) {
         QByteArray name;
@@ -153,6 +165,8 @@ CLFilterRunnable::CLFilterRunnable(CLFilter *filter) :
             platform = platformIds[i];
         else if (isIntel && name.contains(QByteArrayLiteral("Intel")))
             platform = platformIds[i];
+        else if (isAMD && name.contains(QByteArrayLiteral("AMD")))
+            platform = platformIds[i];
     }
     qDebug("Using platform %p", platform);
 
@@ -166,6 +180,18 @@ CLFilterRunnable::CLFilterRunnable(CLFilter *filter) :
                                              CL_GL_CONTEXT_KHR, (cl_context_properties) wglGetCurrentContext(),
                                              CL_WGL_HDC_KHR, (cl_context_properties) wglGetCurrentDC(),
                                              0 };
+#elif defined(Q_OS_LINUX)
+    // An elegant alternative to glXGetCurrentContext. This will even survive
+    // (without interop) when using something other than GLX.
+    QVariant nativeGLXHandle = QOpenGLContext::currentContext()->nativeHandle();
+    QGLXNativeContext nativeGLXContext;
+    if (!nativeGLXHandle.isNull() && nativeGLXHandle.canConvert<QGLXNativeContext>())
+        nativeGLXContext = nativeGLXHandle.value<QGLXNativeContext>();
+    else
+        qWarning("Failed to get the underlying GLX context from the current QOpenGLContext");
+    cl_context_properties contextProps[] = { CL_CONTEXT_PLATFORM, (cl_context_properties) platform,
+                                             CL_GL_CONTEXT_KHR, (cl_context_properties) nativeGLXContext.context(),
+                                             0 };
 #endif
 
     m_clContext = clCreateContextFromType(contextProps, CL_DEVICE_TYPE_GPU, 0, 0, &err);

examples/multimedia/video/qmlvideofilter_opencl/qmlvideofilter_opencl.pro

@@ -12,10 +12,10 @@ OTHER_FILES = main.qml
 target.path = $$[QT_INSTALL_EXAMPLES]/multimedia/video/qmlvideofilter_opencl
 INSTALLS += target
 
-# Edit these as necessary
-osx {
-    LIBS += -framework OpenCL
-} else {
+osx: LIBS += -framework OpenCL
+unix: !osx: LIBS += -lOpenCL
+win32:!winrt {
+    # Edit these as necessary
     INCLUDEPATH += c:/cuda/include
     LIBPATH += c:/cuda/lib/x64
     LIBS += -lopengl32 -lOpenCL