op

Overview ¶

Package op implements operations for updating a user interface.

Gio programs use operations, or ops, for describing their user interfaces. There are operations for drawing, defining input handlers, changing window properties as well as operations for controlling the execution of other operations.

Ops represents a list of operations. The most important use for an Ops list is to describe a complete user interface update to a ui/app.Window's Update method.

Drawing a colored square:

import "github.com/gop9/olt/gio/unit"
import "github.com/gop9/olt/gio/app"
import "github.com/gop9/olt/gio/op/paint"

var w app.Window
var e system.FrameEvent
ops := new(op.Ops)
...
ops.Reset()
paint.ColorOp{Color: ...}.Add(ops)
paint.PaintOp{Rect: ...}.Add(ops)
e.Frame(ops)

State ¶

An Ops list can be viewed as a very simple virtual machine: it has an implicit mutable state stack and execution flow can be controlled with macros.

The StackOp saves the current state to the state stack and restores it later:

ops := new(op.Ops)
var stack op.StackOp
// Save the current state, in particular the transform.
stack.Push(ops)
// Apply a transform to subsequent operations.
op.TransformOp{}.Offset(...).Add(ops)
...
// Restore the previous transform.
stack.Pop()

The CallOp invokes another operation list:

ops := new(op.Ops)
ops2 := new(op.Ops)
op.CallOp{Ops: ops2}.Add(ops)

The MacroOp records a list of operations to be executed later:

ops := new(op.Ops)
var macro op.MacroOp
macro.Record(ops)
// Record operations by adding them.
op.InvalidateOp{}.Add(ops)
...
// End recording.
macro.Stop()

// replay the recorded operations by calling Add:
macro.Add()