From e1248651c8717e686f664279bc0a994b160a5ead Mon Sep 17 00:00:00 2001
From: Egon Elbre <egonelbre@gmail.com>
Date: Sun, 28 Feb 2021 16:20:46 +0200
Subject: [PATCH] layout: automatically add system inset for NewContext

Currently every user needs to manually adjust for system insets.
This is rather verbose and most don't need to deviate from this behavior.

To disable the automatic adjustment, use:

  e.Insets = system.Insets{}
  ctx := layout.NewContext(ops, e)

Signed-off-by: Egon Elbre <egonelbre@gmail.com>
---
 layout/context.go | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/layout/context.go b/layout/context.go
index f47233b8..5d314961 100644
--- a/layout/context.go
+++ b/layout/context.go
@@ -5,6 +5,7 @@ package layout
 import (
 	"time"
 
+	"gioui.org/f32"
 	"gioui.org/io/event"
 	"gioui.org/io/system"
 	"gioui.org/op"
@@ -39,15 +40,30 @@ type Context struct {
 //     Constraints: Exact(e.Size),
 //   }
 //
-// NewContext calls ops.Reset.
+// NewContext calls ops.Reset and adjusts ops for e.Insets.
 func NewContext(ops *op.Ops, e system.FrameEvent) Context {
 	ops.Reset()
+
+	size := e.Size
+
+	if e.Insets != (system.Insets{}) {
+		left := e.Metric.Px(e.Insets.Left)
+		top := e.Metric.Px(e.Insets.Top)
+		op.Offset(f32.Point{
+			X: float32(left),
+			Y: float32(top),
+		}).Add(ops)
+
+		size.X -= left + e.Metric.Px(e.Insets.Right)
+		size.Y -= top + e.Metric.Px(e.Insets.Bottom)
+	}
+
 	return Context{
 		Ops:         ops,
 		Now:         e.Now,
 		Queue:       e.Queue,
 		Metric:      e.Metric,
-		Constraints: Exact(e.Size),
+		Constraints: Exact(size),
 	}
 }