This fix depends on a fix in ign-rendering module, because it
depends on the new Camera::SwapFromThread function
Without it, compilation will fail

Affects gazebosim/gz-rendering#304

Signed-off-by: Matias N. Goldberg <[email protected]>

This avoids us to break ign-rendering ABI while also simplifying the
amount of work to be done

Serializing work is easier to maintain and debug
Only CPU-bound scenario would potentially benefit from parallel command
generation (in terms of UI responsiveness)
Parallel command generation can be added back later

Also fixed coding style

Refer to
gazebosim/gz-rendering#304 (comment)
for discussion

Affects ign-rendering#304

Signed-off-by: Matias N. Goldberg <[email protected]>

Also fixes preexisting race condition when shutting down and improper
uninitialization of the worker thread

Signed-off-by: Matias N. Goldberg <[email protected]>

Fix coding style

Signed-off-by: Matias N. Goldberg <[email protected]>

It's a good thing we went for serializing rendering.

THe way Qt implements the double buffer scheme using signals & slots is
fundamentally flawed because it assumes the worker thread never needs to
synchronize (e.g. to invalidate FBOs if window resolution changes).

Trying to synchronize can easily cause deadlocks if Qt thread has
spurious updates which don't end up emitting TextureInUse, as the worker
thread is running slower than Qt thread.

A way to fix this could be to use a different synchronization mechanism
where the main thread increases a request counter and the worker thread
is constantly looping but only wakes up when that counter is > 0.

For now, this will do.

Signed-off-by: Matias N. Goldberg <[email protected]>

Turn some pointers into references

Signed-off-by: Matias N. Goldberg <[email protected]>

Signed-off-by: Matias N. Goldberg <[email protected]>

Signed-off-by: Matias N. Goldberg <[email protected]>

I changed it because it didn't work, but it must've been old code
because it works now.

Signed-off-by: Matias N. Goldberg <[email protected]>