[hwrdr.native] Blur RenderEffect seems to always use DECAL edge treatment

[chrisbanes]

Description

I'm trying out the new hardware native renderer in Robolectric, through Roborazzi: chrisbanes/haze#147. You'll notice that the blurred content has a white edge around it.

This is what the same content looks like on device:

The issue seems to be that I use RenderEffect.createBlurEffect(..., Shader.TileMode.CLAMP) (here). Robolectric seems to ignore the tile mode provided, and forces the DECAL mode.

For completeness, this is what is displayed on device when I switch to DECAL, which is consistent with the screenshot output:

Expected (Device using CLAMP)	Observed: Robolectric	Device using DECAL

Robolectric & Android Version

Robolectric 4.12

Link to a public git repo demonstrating the problem:

chrisbanes/haze#147

[hoisie]

Cc @ralf-at-android

[hoisie]

Hi Chris,

It looks like, for the current version of native graphics in Robolectric (derived from Android S), blur effect is a GPU-only effect, and does not have a CPU implementation. There is a comment in SKia to this effect, // TODO: Implement CPU backend for different fTileMode.

https://android.googlesource.com/platform/external/skia/+/refs/heads/android12-dev/src/effects/imagefilters/SkBlurImageFilter.cpp#408

There is good news, however. In Android V, there appears to be an implementation of fTileMode for the CPU. So when Android V is released this should start working, if your screenshots target Android V. This is because starting in Android V, Robolectric will use the native libraries built from that specific platform version.

If the fix backports cleanly, we may be able to CP the change from V to RNG's AOSP branch.

[hoisie]

Here is the equivalent issue in the LayoutLib tracker: https://issuetracker.google.com/issues/326101779

[chrisbanes]

Great detective work! Thanks for the update.