Enable/Disable Clips

[rjwignar]

This fixes #19

Following @jminor's suggestion in https://github.com/OpenTimelineIO/raven/pull/27#issuecomment-1879117563, I've been able to use an ImGui::Checkbox() while keeping Item::_enabled private.

Clips will be greyed out when disabled. Re-enabling clips will return them to their original color. Tracks can be enabled/disabled, but this PR does not include UI changes to distinguish enabled from disabled Tracks.

Summary of changes

timeline.cpp:

• In DrawItem(), added conditional greying out on disabled clips
• Disabled non-Gap items have a grey fill_color
  • Obtained by by using UIColorFromName("") to get IM_COL32(0x88, 0x88, 0x88, 0xff)

inspector.cpp:

• Added an "Enabled" checkbox for non-Gap items (Tracks and Clips) using ImGui::Checkbox():

Below is a quick demo of enabling/disabling clips

Strech Goal (Greying of entire tracks):

I'm holding off on this stretch goal as I'm not entirely clear on the desired behaviour, such as whether to grey out the just Track header or the Track header plus every clip the Track contains. I'd be willing to work on this in a follow-up Issue, if it's alright with the team.

Thank you for your patience with this feature and for considering these changes.

[linux-foundation-easycla[bot]]

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[jminor]

Thanks @rjwignar - sorry for overlooking this PR for so long. Your change looks good to me. Are you able/willing to sign the CLA and update the DCO so those checks pass?

[timlehr]

@rjwignar it would be lovely to get your change merged. If you find some time, please look into the CLA / DCO.