tree 7a86cc1c9f2db44204eb86e0ce12da29f5aecf79
parent b63382b4d857f7683e1dc4a11908d35558b9aec0
author Dmitri Shuralyov <dmitshur@golang.org> 1608427064 -0500
committer Dmitri Shuralyov <dmitshur@golang.org> 1608519596 +0000

shiny/iconvg: make SetEllipticalGradient math deterministic

Add explicit rounding in Encoder.SetEllipticalGradient to disable
fused operations. This allows the TestEncodeElliptical case to pass
on GOARCH=arm64. Otherwise, fused multiply-sub instructions are
used on GOARCH=arm64 (but not GOARCH=amd64), which results in a
slightly different real value being computed for a "Set NREG"
instruction (with a tiny delta of 7.450581e-09), and then
encoded into non-identical bytes:

	 ac            Set NREG[NSEL-4] to a real number
	-00                0
	+03 00 00 b2       -7.450581e-09

Document the IconVG design decision that the encoder aims to
produce byte-identical output on all supported platforms per
suggestion in golang.org/issue/43219#issuecomment-748531069.
This should make it clear for the future—if another similar
problem is detected—that the encoder implementation should
be fixed (rather than relaxing Encode tests to allow for
non-deterministic encoding). It also allows package users
to be aware that the encoder is platform-agnostic and not
have to take additional measures themselves. (If this proves
to be truly unsustainable to maintain, it is still viable to
remove it given the "SUBJECT TO INCOMPATIBLE CHANGES" clause.)

Rename TestRasterizer to TestDecodeAndRasterize since it tests
both decoding and rasterizing. There isn't another test that
tests only the Decode function.

Fix some broken links to the material-design-icons repository.

Fixes golang/go#43219.
Updates golang/go#11811.

Change-Id: I5cf15541a4648e408c9c61689041c678c14441bf
Reviewed-on: https://go-review.googlesource.com/c/exp/+/279294
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Nigel Tao <nigeltao@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>