Every tool that has a slider now registers the primary/secondary
sliders and now uses the same keyboard shortcuts to modify the
primary and secondary properties. `[` and `]` for the primary,
`{` and `}` for the secondary.
And also try_create<T> => try_make_ref_counted<T>.
A global "create" was a bit much. The new name matches make<T> better,
which we've used for making single-owner objects since forever.
Some tools (e.g. ZoomTool) doesn't need layer to work. This commit
makes mouse events fire even if there is no layer. This fixes
a bug that ZoomTool didn't work when there is no layers.
This commit adds a Tool::MouseEvent struct, which contains events that
may be needed by tools: layer-relative, image-relative and raw (editor-
relative) event.
The raw event is used by ZoomTool to properly pan the view. This fixes
a bug which caused image to snap out of sight.
This adds on_tool_activation() to Tool which GuideTool can use
to show guides, if they're hidden, when it's activated. Also
show guides on mousedown since there's no use in drawing invisible
guides.
This patch adds the logic for the GuideTool. Pulling in from outside the
image creates a new Guide, moving a Guide outside of the image deletes
it and a Guide can be deleteted via the context menu.
A Guide is considered clicked when the cursor is less than 20 pixels
away from the line.
