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Date: Mon, 11 Jan 2021 10:41:38 +0100
Message-Id: <C8G8AXHM82MW.3AA0U46J6XWFI@testmac>
Cc: 
Subject: Re: [PATCH gio] widget: use correct color in Icon
From: "Elias Naur" <mail@eliasnaur.com>
To: "~egonelbre" <egonelbre@gmail.com>, <~eliasnaur/gio-patches@lists.sr.ht>
References: <161035668868.18065.4407285431413627246-0@git.sr.ht>
In-Reply-To: <161035668868.18065.4407285431413627246-0@git.sr.ht>

On Mon Jan 11, 2021 at 10:04 AM CET, ~egonelbre wrote:
> From: Egon Elbre <egonelbre@gmail.com>
>
> iconvg seems to expect a linear premultiplied color.
>

Thanks. Is it easy to add a test that triggers
https://github.com/golang/go/issues/39526 without your change?

> Signed-off-by: Egon Elbre <egonelbre@gmail.com>
> ---
> internal/f32color/rgba.go | 34 ++++++++++++++++++++++++++++++++
> internal/f32color/rgba_test.go | 36 ++++++++++++++++++++++++++++++++++
> widget/icon.go | 2 +-
> 3 files changed, 71 insertions(+), 1 deletion(-)
> create mode 100644 internal/f32color/rgba_test.go
>
> diff --git a/internal/f32color/rgba.go b/internal/f32color/rgba.go
> index d1b7564..4fc2742 100644
> --- a/internal/f32color/rgba.go
> +++ b/internal/f32color/rgba.go
> @@ -77,6 +77,40 @@ func NRGBAToRGBA(col color.NRGBA) color.RGBA {
> }
> }
> =20
> +// NRGBAToLinearRGBA converts from non-premultiplied sRGB color to
> premultiplied linear RGBA color.
> +//
> +// Each component in the result is `c * alpha`, where `c` is the linear
> color.
> +func NRGBAToLinearRGBA(col color.NRGBA) color.RGBA {
> + if col.A =3D=3D 0xFF {
> + return color.RGBA(col)
> + }
> + c :=3D LinearFromSRGB(col)
> + return color.RGBA{
> + R: uint8(c.R*255 + .5),
> + G: uint8(c.G*255 + .5),
> + B: uint8(c.B*255 + .5),
> + A: col.A,
> + }
> +}
> +
> +// NRGBAToRGBA_PostAlpha converts from non-premultiplied sRGB color to
> premultiplied sRGB color.
> +//
> +// Each component in the result is `sRGBToLinear(c) * alpha`, where `c`
> +// is the linear color.
> +func NRGBAToRGBA_PostAlpha(col color.NRGBA) color.RGBA {
> + if col.A =3D=3D 0xFF {
> + return color.RGBA(col)
> + } else if col.A =3D=3D 0x00 {
> + return color.RGBA{}
> + }
> + return color.RGBA{
> + R: uint8(uint32(col.R) * uint32(col.A) / 0xFF),
> + G: uint8(uint32(col.G) * uint32(col.A) / 0xFF),
> + B: uint8(uint32(col.B) * uint32(col.A) / 0xFF),
> + A: col.A,
> + }
> +}
> +
> // RGBAToNRGBA converts from premultiplied sRGB color to
> non-premultiplied sRGB color.
> func RGBAToNRGBA(col color.RGBA) color.NRGBA {
> if col.A =3D=3D 0xFF {
> diff --git a/internal/f32color/rgba_test.go
> b/internal/f32color/rgba_test.go
> new file mode 100644
> index 0000000..eba1262
> --- /dev/null
> +++ b/internal/f32color/rgba_test.go
> @@ -0,0 +1,36 @@
> +package f32color
> +
> +import (
> + "image/color"
> + "testing"
> +)
> +
> +func TestNRGBAToRGBA_PostAlpha_Boundary(t *testing.T) {
> + for col :=3D 0; col <=3D 0xFF; col++ {
> + for alpha :=3D 0; alpha <=3D 0xFF; alpha++ {
> + in :=3D color.NRGBA{R: uint8(col), A: uint8(alpha)}
> + premul :=3D NRGBAToRGBA_PostAlpha(in)
> + if premul.A !=3D uint8(alpha) {
> + t.Errorf("%v: got %v expected %v", in, premul.A, alpha)
> + }
> + if premul.R > premul.A {
> + t.Errorf("%v: R=3D%v > A=3D%v", in, premul.R, premul.A)
> + }
> + }
> + }
> +}
> +
> +func TestNRGBAToLinearRGBA_Boundary(t *testing.T) {
> + for col :=3D 0; col <=3D 0xFF; col++ {
> + for alpha :=3D 0; alpha <=3D 0xFF; alpha++ {
> + in :=3D color.NRGBA{R: uint8(col), A: uint8(alpha)}
> + premul :=3D NRGBAToLinearRGBA(in)
> + if premul.A !=3D uint8(alpha) {
> + t.Errorf("%v: got %v expected %v", in, premul.A, alpha)
> + }
> + if premul.R > premul.A {
> + t.Errorf("%v: R=3D%v > A=3D%v", in, premul.R, premul.A)
> + }
> + }
> + }
> +}
> diff --git a/widget/icon.go b/widget/icon.go
> index f6f88d3..4e6350d 100644
> --- a/widget/icon.go
> +++ b/widget/icon.go
> @@ -51,7 +51,7 @@ func (ic *Icon) image(sz int) paint.ImageOp {
> img :=3D image.NewRGBA(image.Rectangle{Max: image.Point{X: sz, Y:
> int(float32(sz) * dy / dx)}})
> var ico iconvg.Rasterizer
> ico.SetDstImage(img, img.Bounds(), draw.Src)
> - m.Palette[0] =3D f32color.NRGBAToRGBA(ic.Color)
> + m.Palette[0] =3D f32color.NRGBAToLinearRGBA(ic.Color)
> iconvg.Decode(&ico, ic.src, &iconvg.DecodeOptions{
> Palette: &m.Palette,
> })
> --
> 2.26.2