eglfs: Add support for systems without pbuffer support

Use a small native window and window surface in case the hooks indicate
that pbuffer support is not available.

Change-Id: I6515309041f0e1e2f5321d59941f35d6ee16dca7
Reviewed-by: Louai Al-Khanji <louai.al-khanji@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

2 files changed, 33 insertions, 16 deletions

diff --git a/src/platformsupport/eglconvenience/qeglplatformcontext.cpp b/src/platformsupport/eglconvenience/qeglplatformcontext.cpp
index 1a1e298935..07ef202195 100644
--- a/src/platformsupport/eglconvenience/qeglplatformcontext.cpp
+++ b/src/platformsupport/eglconvenience/qeglplatformcontext.cpp
@@ -187,7 +187,7 @@ void QEGLPlatformContext::init(const QSurfaceFormat &format, QPlatformOpenGLCont
         q_printEglConfig(m_eglDisplay, m_eglConfig);
     }
 
-    updateFormatFromGL();
+    // Cannot just call updateFormatFromGL() since it relies on virtuals. Defer it to initialize().
 }
 
 void QEGLPlatformContext::adopt(const QVariant &nativeHandle, QPlatformOpenGLContext *share)
@@ -238,18 +238,13 @@ void QEGLPlatformContext::adopt(const QVariant &nativeHandle, QPlatformOpenGLCon
     updateFormatFromGL();
 }
 
-void QEGLPlatformContext::updateFormatFromGL()
+void QEGLPlatformContext::initialize()
 {
-#ifndef QT_NO_OPENGL
-    // Have to save & restore to prevent QOpenGLContext::currentContext() from becoming
-    // inconsistent after QOpenGLContext::create().
-    EGLDisplay prevDisplay = eglGetCurrentDisplay();
-    if (prevDisplay == EGL_NO_DISPLAY) // when no context is current
-        prevDisplay = m_eglDisplay;
-    EGLContext prevContext = eglGetCurrentContext();
-    EGLSurface prevSurfaceDraw = eglGetCurrentSurface(EGL_DRAW);
-    EGLSurface prevSurfaceRead = eglGetCurrentSurface(EGL_READ);
+    updateFormatFromGL();
+}
 
+EGLSurface QEGLPlatformContext::createTemporaryOffscreenSurface()
+{
     // Make the context current to ensure the GL version query works. This needs a surface too.
     const EGLint pbufferAttributes[] = {
         EGL_WIDTH, 1,
@@ -257,15 +252,34 @@ void QEGLPlatformContext::updateFormatFromGL()
         EGL_LARGEST_PBUFFER, EGL_FALSE,
         EGL_NONE
     };
+
     // Cannot just pass m_eglConfig because it may not be suitable for pbuffers. Instead,
     // do what QEGLPbuffer would do: request a config with the same attributes but with
     // PBUFFER_BIT set.
     EGLConfig config = q_configFromGLFormat(m_eglDisplay, m_format, false, EGL_PBUFFER_BIT);
-    EGLSurface pbuffer = eglCreatePbufferSurface(m_eglDisplay, config, pbufferAttributes);
-    if (pbuffer == EGL_NO_SURFACE)
-        return;
 
-    if (eglMakeCurrent(m_eglDisplay, pbuffer, pbuffer, m_eglContext)) {
+    return eglCreatePbufferSurface(m_eglDisplay, config, pbufferAttributes);
+}
+
+void QEGLPlatformContext::destroyTemporaryOffscreenSurface(EGLSurface surface)
+{
+    eglDestroySurface(m_eglDisplay, surface);
+}
+
+void QEGLPlatformContext::updateFormatFromGL()
+{
+#ifndef QT_NO_OPENGL
+    // Have to save & restore to prevent QOpenGLContext::currentContext() from becoming
+    // inconsistent after QOpenGLContext::create().
+    EGLDisplay prevDisplay = eglGetCurrentDisplay();
+    if (prevDisplay == EGL_NO_DISPLAY) // when no context is current
+        prevDisplay = m_eglDisplay;
+    EGLContext prevContext = eglGetCurrentContext();
+    EGLSurface prevSurfaceDraw = eglGetCurrentSurface(EGL_DRAW);
+    EGLSurface prevSurfaceRead = eglGetCurrentSurface(EGL_READ);
+
+    EGLSurface tempSurface = createTemporaryOffscreenSurface();
+    if (eglMakeCurrent(m_eglDisplay, tempSurface, tempSurface, m_eglContext)) {
         if (m_format.renderableType() == QSurfaceFormat::OpenGL
             || m_format.renderableType() == QSurfaceFormat::OpenGLES) {
             const GLubyte *s = glGetString(GL_VERSION);
@@ -303,7 +317,7 @@ void QEGLPlatformContext::updateFormatFromGL()
         }
         eglMakeCurrent(prevDisplay, prevSurfaceDraw, prevSurfaceRead, prevContext);
     }
-    eglDestroySurface(m_eglDisplay, pbuffer);
+    destroyTemporaryOffscreenSurface(tempSurface);
 #endif // QT_NO_OPENGL
 }
 
diff --git a/src/platformsupport/eglconvenience/qeglplatformcontext_p.h b/src/platformsupport/eglconvenience/qeglplatformcontext_p.h
index 7825c7b3d7..b922584554 100644
--- a/src/platformsupport/eglconvenience/qeglplatformcontext_p.h
+++ b/src/platformsupport/eglconvenience/qeglplatformcontext_p.h
@@ -59,6 +59,7 @@ public:
                         EGLConfig *config = 0, const QVariant &nativeHandle = QVariant());
     ~QEGLPlatformContext();
 
+    void initialize();
     bool makeCurrent(QPlatformSurface *surface);
     void doneCurrent();
     void swapBuffers(QPlatformSurface *surface);
@@ -74,6 +75,8 @@ public:
 
 protected:
     virtual EGLSurface eglSurfaceForPlatformSurface(QPlatformSurface *surface) = 0;
+    virtual EGLSurface createTemporaryOffscreenSurface();
+    virtual void destroyTemporaryOffscreenSurface(EGLSurface surface);
 
 private:
     void init(const QSurfaceFormat &format, QPlatformOpenGLContext *share);