Update blocks menu contents without re-rendering the whole thing

[ericrosenbaum]

Expected Behavior

We should be able to change the set of blocks in the flyout (containing all of the blocks - PR here) without re-rendering the entire flyout (otherwise, the update will be very slow). The cases include:

• Switching to or from the stage (which excludes some blocks, and adds others)
• Creating a variable
• Switching sprites, to update the displayed local variable reporter blocks
• Adding an extension

Actual Behavior

Currently, we don't have a way to update only part of the blocks menu.

Notes from @rachel-fenichel

This means you want to remove (or add) some blocks; render any new blocks; not render any old blocks; then reflow the flyout.

Currently reflow assumes that it only needs to shuffle things horizontally (in the vertical flyout) so we'll need to modify that.

When you delete a block there are a few things that need deleting:

• the rectangle behind the block (click target)
• the block itself
• the block's checkbox, if it exists
• the mouse listeners corresponding to the block

The mouse listeners are just kept in a list right now, with no attention paid to the correspondence between listeners and blocks. You'll need to change that.

Other notes

When we update the flyout on switching sprites, the scroll position will need to be updated if the flyout has changed in length. I think the simplest thing will be to store the selected category and scroll to it after the update.

[towerofnix]

When we update the flyout on switching sprites, the scroll position will need to be updated if the flyout has changed in length. I think the simplest thing will be to store the selected category and scroll to it after the update.

Would keeping track of the scroll offset past the selected category work better? That way if you're scrolled part way down a long category (e.g. Control, or an extension with many blocks), you'll still be scrolled the same distance down it.