Design - Zoom controls

[thisandagain]

In Scratch on web / desktop we have zoom controls in the bottom right of the editor:

For tablet and desktop / web, we should make a decision as to what we want:

• No controls (no zooming)
• Button controls
• Pinch to zoom controls

One consideration is that "pinch to zoom" will impact the potential for multitouch interaction with blocks.

/cc @tmickel

[NeilFraser]

Minor point: The "=" button on Scratch zooms to 100%, where as its equivalent in Blockly zooms to 100% and also snaps to the center of the workspace. I think snapping to the center is better (otherwise one can end up looking way offscreen), but this functionality can be disabled if you want to keep the Scratch behaviour.

[tmickel]

Is it even possible to properly support pinch-to-zoom on desktop? I'd say no given that many users will be using a mouse (and I'm pretty sure JavaScript click events don't support multiple pointers/gestures).

We could go for pinch-to-zoom on touch and button controls on desktop, if we're willing to have an inconsistent experience.

Or, my preferred approach would be having buttons on both platforms, which would let us do multi-touch on tablets/phones.

[NeilFraser]

If the desktop only has a mouse, then pinch-to-zoom is impossible. But we definitely want to support pinch-to-zoom on desktops with trackpads, touch screens, or other multi-touch inputs. JS exposes a list of touch points, the rest is just math.

[tmickel]

On my Macbook no touch events seem to be generated in browsers (in Google Maps, for example, the whole page zooms, not just the map frame). I'm assuming devices with touch screens might work. We'd also need to disable page-level zooming triggered by multitouch gestures in the browser.