GridState Modes refactor, take 2

Status: proposal See also: xword-state-modes.md

Summary

Supplement the GridStateMode enum with a set of distinct behaviors. These behaviors can be set individually on a state.

This will make grid-state.c easier to understand and debug (and test), as well as let us create modes on demand later on.

Rationale

The current grid modes have been created on demand when we need a new grid type. The modes combine some rendering options, cursor behaviors, and thematic functionality all in one. They are hard to reason about, and have proven fragile and brittle over time.

Proposal

We decompose the current modes into a set of behaviors that are independently settable. The current modes are:

typedef enum
{
  GRID_STATE_SOLVE,       /* @ Solve a crossword @ */
  GRID_STATE_BROWSE,      /* @ Browse through a board without modifying it @ */
  GRID_STATE_EDIT,        /* @ Edit the grid @ */
  GRID_STATE_EDIT_BROWSE, /* @ Browse through an editable board without modifying it @ */
  GRID_STATE_SELECT,      /* @ Select cells @ */
  GRID_STATE_VIEW,        /* @ Display a board with no interaction @ */
} GridStateMode;

The decomposition into behaviors looks like:

	USE_CURSOR	SHOW_GUESS	SELECTABLE	EDIT_CELLS	NORMAL_ONLY	QUIRKS_ADVANCE
SOLVE	true	true	false	true	true	true
BROWSE	true	true	false	false	true	false
EDIT	true	false	false	true	false	false
EDIT_BROWSE	true	false	false	false	true	false
SELECT	true	true	true	false	true	false
VIEW	false	false	false	false	false	false

Each behavior is described below:

• USE_CURSOR: The state has a valid cursor

• SHOW_GUESS: The grid displays the guess instead of the solution in a cell

• SELECTABLE: The grid can select cells

• EDIT_CELLS: The grid allows the user to edit the cel

• NORMAL_ONLT: The grid only allows the cursor to exist on normal cells. BLOCK and NULL cells can’t have a cursor set

• QUIRKS_ADVANCE: Whether to honor the quirks GuessAdvance setting when going to the next cell after a guess.

This set of booleans is represented by the GridState.behavior bitfield. Setting the mode will set the bitfield to a well known state.

Changing the behavior afterwards is possible. We will add a GRID_STATE_CUSTOM mode to capture when that has happened.

NOTE: Not all combinations of behaviors are valid. Some also interact, such as CURSOR_ONLY_NORMAL and SELECTABLE

Other Considerations

• Selection may need multiple selection types (like GtkEditable, for instance.)

• We also want an overlay mode for things like reveal errors, or heat maps. That might factor into this design.

• Once we’ve validated the behavior bitfield and fully migrated, we may remove the mode attribute from the state in order to avoid confusion. We won’t go away completely from the modes, but just use them as a short-hand for setting well-known combinations of behaviors.