Dragging blocks causes the blocks pane to change size

[rschamp]

Expected Behavior

Please describe what should happen
When I drag a block from the toolbox, nothing on the screen should move except for the block.

Actual Behavior

Describe what actually happens
When I drag a block from the toolbox, the right side of the page shifts ~20px to the left, slipping under the blocks pane.

Steps to Reproduce

Explain what someone needs to do in order to see what's described in Actual behavior above
Drag a block from the toolbox.

If you revert #263 the issue goes away, but I'm not sure what exactly introduced it, since that was so long ago. It seems to be related to the .injectionDiv toggling between overflow: hidden and visible on drags.

Operating System and Browser

Chrome 57

[paulkaplan]

So this is because we have been using the injectionDiv to contain the workspace (to do things like the rounded corner radius and correct borders). The problem with that is on drag, the injectionDiv gets set to overflow: visible to allow you to drag blocks outside the workspace (to anywhere on the page...) That functionality is intentional (see note in code https://github.com/LLK/scratch-blocks/blob/develop/core/block_drag_surface.js#L112-L117). If we want to maintain that functionality, we need to change the way we are styling the injectionDiv, because we can no longer use it as a clipping container.

Oh the jumping itself is caused by the overflow:visible causing a 1px increase in height causing the vertical scrollbar to appear.

[paulkaplan]

One way to easily fix this is to just set overfloy-y: hidden on the body of the page. Since this is a sigle page app that never scrolls vertically, this probably would be fine. cc @lifeinchords ?

[rschamp]

The only issue I see with that is that we would eventually want page scrolling similar to on 2.0, where you are alway able to scroll to the first row of sprites, even if your window is very short.

The long term fix sounds like reverting #263 and do the real fix for that in scratch-blocks?