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https://git.sr.ht/~eliasnaur/gio
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Elias Naur
85 lines
2.2 KiB
Go
85 lines
2.2 KiB
Go
// SPDX-License-Identifier: Unlicense OR MIT
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/*
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Package ui defines operations buffers, units and common operations
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for GUI programs written with the Gio module.
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See https://gioui.org for instructions to setup and run Gio programs.
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Operations
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Gio programs use operations, or ops, for describing their user
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interfaces. There are operations for drawing, defining input
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handlers, changing window properties as well as operations for
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controlling the execution of other operations.
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Ops represents a list of operations. The most important use
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for an Ops list is to describe a complete user interface update
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to a ui/app.Window's Update method.
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Drawing a colored square:
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import "gioui.org/ui"
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import "gioui.org/ui/app"
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import "gioui.org/ui/paint"
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var w app.Window
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var ops ui.Ops
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...
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ops.Reset()
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paint.ColorOp{Color: ...}.Add(ops)
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paint.PaintOp{Rect: ...}.Add(ops)
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w.Update(ops)
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State
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An Ops list can be viewed as a very simple virtual machine: it has an implicit
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mutable state stack and execution flow can be controlled with macros.
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The StackOp saves the current state to the state stack and restores it later:
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var ops ui.Ops
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var stack ui.StackOp
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// Save the current state, in particular the transform.
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stack.Push(ops)
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// Apply a transform to subsequent operations.
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ui.TransformOp{}.Offset(...).Add(ops)
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...
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// Restore the previous transform.
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stack.Pop()
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The MacroOp records a list of operations to be executed later:
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var ops ui.Ops
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var macro ui.MacroOp
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macro.Record()
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// Record operations by adding them.
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ui.InvalidateOp{}.Add(ops)
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...
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macro.Stop()
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...
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// Execute the recorded operations.
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macro.Add(ops)
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Note that operations added between Record and Stop are not executed until
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the macro is Added.
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Units
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A Value is a value with a Unit attached.
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Device independent pixel, or dp, is the unit for sizes independent of
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the underlying display device.
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Scaled pixels, or sp, is the unit for text sizes. An sp is like dp with
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text scaling applied.
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Finally, pixels, or px, is the unit for display dependent pixels. Their
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size vary between platforms and displays.
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To maintain a constant visual size across platforms and displays, always
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use dps or sps to define user interfaces. Only use pixels for derived
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values.
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*/
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package ui
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