Errors and saved state

Errors

Functions that can fail return Result<T>:

• It holds either the value or an Error.
• An Error has an ErrorCode and a message.
• It converts to true when it holds the value.

if (tachyon::Result<void> result = app.Initialize(); !result)
    std::fprintf(stderr, "%s\n", result.GetError().message.c_str());

• Value access: Value(), operator*, operator->, ValueOr(fallback).
• Error codes: Failed, InvalidArgument, NotFound, ParseFailed, Unsupported, OutOfMemory, DeviceLost.
• These return a Result:
  • Initialize
  • Run
  • RecordFrame
  • ReadWindowPixels
  • RestoreUIState

• ThemeReloadResult() gives the outcome of the last RequestReloadTheme:

  if (const Result<void>& reload = ThemeReloadResult(); !reload)
      Text(reload.GetError().message);

Saved UI state

The library saves UI state as JSON text, and you store that text where you like. Register once what to keep:

• Each thing is registered under a key, a string you choose. Keys must stay the same between runs.
• The objects you name must outlive the call.

PersistWindow("main", mainWindowID);         // position, size, mode and monitor
PersistDocking("dock", dockingLayout);       // panels by type, else title
PersistTable("assets", tableState, columns); // column widths and order
PersistValue("zoom", zoom);                  // an app setting (bool, int, float, string)

There is also:

• PersistToolbars

• PersistShortcuts, for the shortcuts the user changed. Register the commands before RestoreUIState; the others keep the shortcuts the app gives them:

  PersistShortcuts("shortcuts", commandManager);

• PersistDocuments, for each main window's documents (see Documents in Tabs, docking and toolbars)

Save and restore:

std::string json = app.SaveUIState();                        // e.g. after Run()
 
if (tachyon::Result<void> restored = RestoreUIState(json); !restored)
    std::fprintf(stderr, "UI state not restored: %s\n", restored.GetError().message.c_str());

• RestoreUIState applies everything at once, except windows. Those apply the next time you declare them.
• Unknown keys, panels and columns are skipped.

Window placement on restore, in order:

1. The monitor it was saved on.
2. If that is gone, the same place on a monitor of the same size.
3. Otherwise the primary monitor, resized to fit its work area.
4. If the top edge would still be off every monitor, only the size is restored.

The demo calls the Persist* functions and RestoreUIState at the end of Initialize, and SaveUIState after Run() returns.

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