diff options
Diffstat (limited to 'src/plugins/platforms/qnx')
| -rw-r--r-- | src/plugins/platforms/qnx/qqnxwindow.cpp | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/src/plugins/platforms/qnx/qqnxwindow.cpp b/src/plugins/platforms/qnx/qqnxwindow.cpp index 95050aa05c..4032685e3e 100644 --- a/src/plugins/platforms/qnx/qqnxwindow.cpp +++ b/src/plugins/platforms/qnx/qqnxwindow.cpp @@ -385,6 +385,28 @@ void QQnxWindow::scroll(const QRegion ®ion, int dx, int dy, bool flush) void QQnxWindow::post(const QRegion &dirty) { + // How double-buffering works + // -------------------------- + // + // The are two buffers, the previous one and the current one. + // The previous buffer always contains the complete, full image of the whole window when it + // was last posted. + // The current buffer starts with the complete, full image of the second to last posting + // of the window. + // + // During painting, Qt paints on the current buffer. Thus, when Qt has finished painting, the + // current buffer contains the second to last image plus the newly painted regions. + // Since the second to last image is too old, we copy over the image from the previous buffer, but + // only for those regions that Qt didn't paint (because that would overwrite what Qt has just + // painted). This is the copyBack() call below. + // + // After the call to copyBack(), the current buffer contains the complete, full image of the + // whole window in its current state, and we call screen_post_window() to make the new buffer + // available to libscreen (called "posting"). There, only the regions that Qt painted on are + // posted, as nothing else has changed. + // + // After that, the previous and the current buffers are swapped, and the whole cycle starts anew. + // Check if render buffer exists and something was rendered if (m_currentBufferIndex != -1 && !dirty.isEmpty()) { qWindowDebug() << Q_FUNC_INFO << "window =" << window(); |