Return values, content and units

Return values and callbacks

A control reports a change in two ways; use either:

• The callback is a function you pass to the control. It runs in the input step of the frame that received the input.
• The return value is true in the next frame's OnGUI.

// A callback.
Button("Greet", [this] { greeting = "Hello, " + name + "!"; });
 
// The return value.
if (Button("Reset", nullptr))
    ResetSettings();

Value editors take the value by reference:

• They write to it directly.
• They return whether it changed.

Field(name);                    // std::string
Field(enabled, "Enabled");      // bool, with its label
if (Field(scale))               // float
    ApplyScale(scale);

Overloads per control: Controls.

GUIContent

A control shows a GUIContent:

• text, an icon, or both
• an optional tooltip

Strings and icons convert to it:

Button("Save", onSave);
Button(saveIcon, onSave);
Button({ saveIcon, "Save", "Write the file to disk" }, onSave);
Button({ "Save", "Write the file to disk" }, onSave);   // text and tooltip

Its strings are std::string_view, so they only need to live for the duration of the call. A local string is fine:

const std::string title = "Save " + fileName;
Button(title, onSave);

Units

• Sizes you pass in are CSS px, scaled by the UI scale like stylesheet sizes.
• Positions, rects and sizes the library measured or computed are whole device pixels.

tachyon::LayoutOverride{}.Width(200)                            // 200 CSS px: 300 pixels at 150%
tachyon::LayoutOverride{}.Width(tachyon::Pixels{ measured })  // already pixels, used as is

• A plain int converts to CssPx; Pixels must be written explicitly.
• int2 and IntRect are always pixels.

• The UI scale is the main window's display scale times the zoom:

  • set the zoom with SetUIScale(scale)
  • a zoom of 1 follows the OS

  SetUIScale(1.25f);

• styleManager.Px(n) converts CSS px to pixels, for example for custom drawing:

  const int margin = styleManager.Px(8);   // 8 CSS px, in pixels

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