facebook/fresco

Overlay drawable alpha value not respected

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#1905 opened on Sep 18, 2017

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 (1 comment) (2 reactions) (1 assignee)Java (17,072 stars) (3,750 forks)batch import
buggood first issuehelp wanted

Description

Description

Reported via StackOverflow: https://stackoverflow.com/questions/45971482/translucent-image-overlay-drawable-loses-alpha

If you set an overlay drawable, the alpha value will always be set to 255, no matter what the actual alpha value is.

Reproduction

Drawable drawable = ...;
drawable.setAlpha(50);
draweeView.getHierarchy().setOverlayImage(drawable);

The alpha value of the drawable will be 255 instead of 50.

Solution

The reason for this is that a FadeDrawable holds all drawables of the drawee hierarchy and fades between them as needed - but does not respect initial alpha values.

Additional Information

  • Fresco version: 1.5.0
  • Platform version: All platforms

Contributor guide

Tech stack
javaandroid
Domain
mobile
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
JavaAndroid drawablesFresco library basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the FadeDrawable class in Fresco's source code to understand how it handles drawable alpha values. The issue points out that FadeDrawable resets alpha to 255 when setting overlay images. Look at the setAlpha and fade methods in FadeDrawable.java to see how initial alpha values are ignored. Consider modifying the constructor or adding a method to preserve the drawable's original alpha.