e4ui-fix_sash_dragging.md

Fix random freeze caused by dragging sash in Eclipse SWT Renderer

Fix random freeze happened during dragging inside MPartSashContainer. The freeze only appears when there are OpenGL canvases in MPart and the freeze point is SetWindowPos or EndDeferWindowPos, for reasons unknown.

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Modify org.eclipse.e4.ui.workbench.renderers.swt

org.eclipse.e4.ui.workbench.renderers.swt.SashLayout

Under constructor SashLayout(host, root), inside MouseMoveListener remove the host.layout() calls:

host.addMouseMoveListener(new MouseMoveListener() {
    @Override
    public void mouseMove(final MouseEvent e) {
        ...
        ...
        adjustWeights(sashesToDrag, e.x, e.y);
        host.layout();                                          // REMOVE
        host.update();                                          // REMOVE
        if (!updateHostInProgress) {                            // INSERT
            updateHostInProgress = true;                        // INSERT
            host.getDisplay().timerExec(50, this::updateHost);  // INSERT
        }                                                       // INSERT
        ...
        ...
    }
    private void updateHost() {                                 // INSERT
        updateHostInProgress = false;                           // INSERT
        host.layout();                                          // INSERT
        host.update();                                          // INSERT
    }                                                           // INSERT
    private boolean updateHostInProgress;                       // INSERT
});

Under constructor SashLayout(host, root), inside addMouseListener insert the host.layout() calls:

host.addMouseListener(new MouseListener() {
    @Override
    public void mouseUp(MouseEvent e) {
        host.setCapture(false);
        draggingSashes = false;
        host.layout();                                          // INSERT
        host.update();                                          // INSERT
    }
    ...
    ...