DEV/flutter_flutter
1
0
Fork 0
mirror of https://github.com/flutter/flutter.git synced 2026-02-20 02:29:02 +08:00
Code Issues Packages Projects Releases Wiki Activity

Explain why Opacity could be slow (#24255)

Browse Source
This commit is contained in:
liyuqian 2018-11-20 15:27:21 -08:00 committed by GitHub
parent 5251306886
commit d9ad220bbb
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 15 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
packages/flutter/lib/src/widgets/basic.dart
View File

@ -156,12 +156,17 @@ class Directionality extends InheritedWidget {
///
/// ## Transparent image
///
/// If only a single [Image] needs to be composited with an opacity between 0.0
/// and 1.0, it's much faster to directly use [Image].
/// If only a single [Image] or [Color] needs to be composited with an opacity
/// between 0.0 and 1.0, it's much faster to directly use them without [Opacity]
/// widgets.
///
/// For example, `Container(color: Color.fromRGBO(255, 0, 0, 0.5))` is much
/// faster than `Opacity(opacity: 0.5, child: Container(color: Colors.red))`.
///
/// {@tool sample}
///
/// This example draws an [Image] with 0.5 opacity:
/// The following example draws an [Image] with 0.5 opacity without using
/// [Opacity]:
///
/// ```dart
/// Image.network(
@ -170,8 +175,15 @@ class Directionality extends InheritedWidget {
/// colorBlendMode: BlendMode.modulate
/// )
/// ```
///
/// {@end-tool}
///
/// Directly drawing an [Image] or [Color] with opacity is faster than using
/// [Opacity] on top of them because [Opacity] could apply the opacity to a
/// group of widgets and therefore a costly offscreen buffer will be used.
/// Drawing content into the offscreen buffer may also trigger render target
/// switches and such switching is particularly slow in older GPUs.
///
/// See also:
///
/// * [Visibility], which can hide a child more efficiently (albeit less