Keyboard Selection Spec

.github/actions/spell-check/expect/expect.txt

@@ -203,6 +203,8 @@ CARETBLINKINGENABLED
 CARRIAGERETURN
 cascadia
 catid
+carlos
+zamora
 cazamor
 CBash
 cbegin
@@ -2642,6 +2644,7 @@ WINDOWPOSCHANGING
 windowproc
 windowrect
 windowsapp
+windowsdeveloper
 windowsinternalstring
 WINDOWSIZE
 windowsx

doc/specs/Keyboard-Selection.md

@@ -0,0 +1,138 @@
+---
+author: Carlos Zamora @carlos-zamora
+created on: 2019-08-30
+last updated: 2020-05-7
+issue id: #715
+---
+
+# Keyboard Selection
+
+## Abstract
+
+This spec describes a new set of keybindings that allows the user to create and update a selection without the use of a mouse or stylus.
+
+## Inspiration
+
+ConHost allows the user to modify a selection using the keyboard. Holding `Shift` allows the user to move the second selection endpoint in accordance with the arrow keys. The selection anchor updates by one cell per key event, allowing the user to refine the selected region.
+
+Mark mode allows the user to create a selection using only the keyboard, then edit it as mentioned above.
+
+
+## Solution Design
+
+The fundamental solution design for keyboard selection is that the responsibilities between the Terminal Control and Terminal Core must be very distinct. The Terminal Control is responsible for handling user interaction and directing the Terminal Core to update the selection. The Terminal Core will need to update the selection according to the preferences of the Terminal Control.
+
+
+### Fundamental Terminal Control Changes
+
+`TermControl::_KeyDownHandler()` is responsible for interpreting the key events. At the time of writing this spec, there are 3 cases handled in this order:
+- Alt+Gr events
+- Keybindings
+- Send Key Event (also clears selection)
+
+Conditionally effective keybindings can be introduced to update the selection accordingly. A well known conditionally effective keybinding is the `Copy` action where text is copied if a selection is active, otherwise the key event is marked as `handled = false`. See "UI/UX Design" --> "Keybindings" for more information regarding keybindings.
+
+#### Idea: Make keyboard selection a simulation of mouse selection
+It may seem that some effort can be saved by making the keyboard selection act as a simulation of mouse selection. There is a union of mouse and keyboard activity that can be represented in a single set of selection motion interfaces that are commanded by the TermControl's Mouse/Keyboard handler and adapted into appropriate motions in the Terminal Core.
+
+However, the mouse handler operates by translating a pixel coordinate on the screen to a text buffer coordinate. This would have to be rewritten and the approach was deemed unworthy.
+
+
+### Fundamental Terminal Core Changes
+
+The Terminal Core will need to expose a `MoveSelectionEndpoint()` function that is called by the keybinding handler. The following parameters will need to be passed in:
+- `enum Direction`: the direction that the selection anchor will attempt to move to. Possible values include `Up`, `Down`, `Left`, and `Right`.
+- `enum SelectionExpansionMode`: the selection expansion mode that the selection anchor will adhere to. Possible values include `Cell`, `Word`, `Viewport`, `Buffer`.
+
+For `SelectionExpansionMode = Cell`, the selection anchor will be updated according to the buffer's output pattern. For **horizontal movements**, the selection anchor will attempt to move left or right. If a viewport boundary is hit, the anchor will wrap appropriately (i.e.: hitting the left boundary moves it to the last cell of the line above it).
+
+For **vertical movements**, the selection anchor will attempt to move up or down. If a **viewport boundary** is hit and there is a scroll buffer, the anchor will move and scroll accordingly by a line. If a **buffer boundary** is hit, the anchor will not move. In this case, however, the event will still be considered handled.
+
+For `SelectionExpansionMode = Word`, the selection anchor will also be updated according to the buffer's output pattern, as above. However, the selection will be updated in accordance with "chunk selection" (performing a double-click and dragging the mouse to expand the selection). For **horizontal movements**, the selection anchor will be updated according to the `_ExpandDoubleClickSelection` functions. The result must be saved to the anchor. As before, if a boundary is hit, the anchor will wrap appropriately.
+
+For **vertical movements**, the movement is a little more complicated than before. The selection will still respond to buffer and viewport boundaries as before. If the user is trying to move up, the selection anchor will attempt to move up by one line, then selection will be expanded leftwards. Alternatively, if the user is trying to move down, the selection anchor will attempt to move down by one line, then the selection will be expanded rightwards.
+
+For `SelectionExpansionMode = Viewport`, the selection anchor will be updated according to the viewport's height. Horizontal movements will be updated according to the viewport's width, thus resulting in the anchor being moved to the left/right boundary of the viewport.
+
+**NOTE**: An important thing to handle properly in all cases is wide glyphs. The user should not be allowed to select a portion of a wide glyph; it should be all or none of it. When calling `_ExpandWideGlyphSelection` functions, the result must be saved to the anchor.
+
+**NOTE**: In all cases, horizontal movements attempting to move past the left/right viewport boundaries result in a wrap. Vertical movements attempting to move past the top/bottom viewport boundaries will scroll such that the selection is at the edge of the screen. Vertical movements attempting to move past the top/bottom buffer boundaries will be clamped to be within buffer boundaries.
+
+Every combination of the `Direction` and `SelectionExpansionMode` will map to a keybinding. These pairings are shown below in the UI/UX Design --> Keybindings section.
+
+**NOTE**: If `copyOnSelect` is enabled, we need to make sure we update the clipboard on every change in selection.
+
+
+## UI/UX Design
+
+### Keybindings
+
+Thanks to Keybinding Args, there will only be 2 new commands that need to be added:
+| Action | Keybinding Args | Description |
+|--|--|--|
+| `moveSelectionPoint` |                                                               | If a selection exists, moves the last selection anchor.
+|                       | `Enum direction { up, down, left, right}`                     | The direction the selection will be moved in. |
+|                       | `Enum expansionMode { cell, word, line, viewport, buffer }`   | The context for which to move the selection anchor to. (defaults to `cell`)
+| `selectEntireBuffer`  | | Select the entire text buffer.
+
+
+By default, the following keybindings will be set:
+```JS
+// Cell Selection
+{ "command": { "action": "moveSelectionPoint", "direction": "down" },  "keys": ["shift+down"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "up" },    "keys": ["shift+up"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "left" },  "keys": ["shift+left"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "right" }, "keys": ["shift+right"] },
+
+// Word Selection
+{ "command": { "action": "moveSelectionPoint", "direction": "left",    "expansionMode": "word" }, "keys": ["ctrl+shift+left"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "right",   "expansionMode": "word" }, "keys": ["ctrl+shift+right"] },
+
+// Viewport Selection
+{ "command": { "action": "moveSelectionPoint", "direction": "left",    "expansionMode": "viewport" }, "keys": ["shift+home"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "right",   "expansionMode": "viewport" }, "keys": ["shift+end"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "up",      "expansionMode": "viewport" }, "keys": ["ctrl+shift+up"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "down",    "expansionMode": "viewport" }, "keys": ["ctrl+shift+down"] },
+
+// Buffer Corner Selection
+{ "command": { "action": "moveSelectionPoint", "direction": "up",      "expansionMode": "buffer" }, "keys": ["ctrl+shift+home"] },
+{ "command": { "action": "moveSelectionPoint", "direction": "down",    "expansionMode": "buffer" }, "keys": ["ctrl+shift+end"] },
+
+// Select All
+{ "command": "selectEntireBuffer", "keys": ["ctrl+shift+a"] },
+```
+
+## Capabilities
+
+### Accessibility
+
+Using the keyboard is generally a more accessible experience than using the mouse. Being able to modify a selection by using the keyboard is a good first step towards making selecting text more accessible.
+
+### Security
+
+N/A
+
+### Reliability
+
+With regards to the Terminal Core, the newly introduced code should rely on already existing and tested code. Thus no crash-related bugs are expected.
+
+With regards to Terminal Control and the settings model, crash-related bugs are not expected. However, ensuring that the selection is updated and cleared in general use-case scenarios must be ensured.
+
+### Compatibility
+
+N/A
+
+### Performance, Power, and Efficiency
+
+## Potential Issues
+
+The settings model makes all of these features easy to disable, if the user wishes to do so.
+
+## Future considerations
+
+This functionality will be expanded to create a feature similar to Mark Mode. This will allow a user to create a selection using only the keyboard.
+
+
+## Resources
+
+- https://blogs.windows.com/windowsdeveloper/2014/10/07/console-improvements-in-the-windows-10-technical-preview/