1013540 - Skia gradients are biased downwards

Status: RESOLVED INVALID

(Core :: Graphics, defect)

Description

[Jeff Muizelaar [:jrmuizel]]

Attachment: Remove bias from gradients

Comment 1

[Jeff Muizelaar [:jrmuizel]]

Attachment: Remove bias from gradients

Comment 2

[Jeff Muizelaar [:jrmuizel]]

Attachment: Remove bias from gradients

This removes the 0.5 bias that was added before doing the transformation. A similar thing is done in AFFINE_FILTER_NAME in SkBitmapProcState_matrix.h

Comment 3

[Jeff Muizelaar [:jrmuizel]]

George, can you get this upstreamed?

Comment 4

[George Wright (:gw280) (needinfo me!)]

I can try

Comment 5

[George Wright (:gw280) (needinfo me!)]

https://codereview.chromium.org/464923004

Comment 6

[Lee Salzman [:lsalzman]]

Attachment: fix offsetting of Skia's vertical linear gradients

The issue is more or less as the previous patch describes, that when linear filtering is applied we need to make sure we subtract the offset of half a texel.

However, we need to ensure that this only happens when we are actually doing a form of linear filtering. This only occurs in shadeSpan_linear_vertical_lerp - a strictly vertical gradient in the 32bpp case. The other cases don't try to emulate any sort of linear filtering so shouldn't have the half-texel offset.

The fix ends up just being a one-liner.

Comment 7

[Lee Salzman [:lsalzman]]

This code no longer exists in recent versions of Skia, so I am going to mark this as invalid. If a similar issue turns up in the new Skia code, we can file a new bug.