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internal/f32color: add colorspace-correct function for alpha scaling

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Package material's ad-hoc mulAlpha didn't take the sRGB color-space
into account, which meant that alpha-scaled colors were subtly wrong.
Introduce f32color.MulAlpha and convert all uses to it.

Thanks to René Post for finding and debugging the issue.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
This commit is contained in:
Elias Naur
2020-09-28 09:02:38 +02:00
parent 679a34b116
commit 4bab6fcf32
7 changed files with 31 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files
internal/f32color/rgba.go
+12
View File
@@ -73,3 +73,15 @@ func sRGBToLinear(c float32) float32 {
return float32(math.Pow(float64((c+0.055)/1.055), 2.4))
}
}
// MulAlpha scales all color components by alpha/255.
func MulAlpha(c color.RGBA, alpha uint8) color.RGBA {
// TODO: Optimize. This is pretty slow.
a := float32(alpha) / 255.
rgba := RGBAFromSRGB(c)
rgba.A *= a
rgba.R *= a
rgba.G *= a
rgba.B *= a
return rgba.SRGB()
}
widget/material/button.go
+6 -4
View File
@@ -8,6 +8,7 @@ import (
"math"
"gioui.org/f32"
"gioui.org/internal/f32color"
"gioui.org/io/pointer"
"gioui.org/layout"
"gioui.org/op"
@@ -131,7 +132,7 @@ func (b ButtonLayoutStyle) Layout(gtx layout.Context, w layout.Widget) layout.Di
}.Add(gtx.Ops)
background := b.Background
if gtx.Queue == nil {
background = mulAlpha(b.Background, 150)
background = f32color.MulAlpha(b.Background, 150)
}
dims := fill(gtx, background)
for _, c := range b.Button.History() {
@@ -159,7 +160,7 @@ func (b IconButtonStyle) Layout(gtx layout.Context) layout.Dimensions {
}.Add(gtx.Ops)
background := b.Background
if gtx.Queue == nil {
background = mulAlpha(b.Background, 150)
background = f32color.MulAlpha(b.Background, 150)
}
dims := fill(gtx, background)
for _, c := range b.Button.History() {
@@ -273,9 +274,10 @@ func drawInk(gtx layout.Context, c widget.Press) {
size *= sizeBezier
alpha := 0.7 * alphaBezier
const col = 0.8
ba, bc := byte(alpha*0xff), byte(alpha*col*0xff)
ba, bc := byte(alpha*0xff), byte(col*0xff)
defer op.Push(gtx.Ops).Pop()
ink := paint.ColorOp{Color: color.RGBA{A: ba, R: bc, G: bc, B: bc}}
rgba := f32color.MulAlpha(color.RGBA{A: 0xff, R: bc, G: bc, B: bc}, ba)
ink := paint.ColorOp{Color: rgba}
ink.Add(gtx.Ops)
rr := size * .5
op.Offset(c.Position.Add(f32.Point{
widget/material/checkable.go
+2 -1
View File
@@ -6,6 +6,7 @@ import (
"image"
"image/color"
"gioui.org/internal/f32color"
"gioui.org/io/pointer"
"gioui.org/layout"
"gioui.org/op/paint"
@@ -42,7 +43,7 @@ func (c *checkable) layout(gtx layout.Context, checked bool) layout.Dimensions {
size := gtx.Px(c.Size)
icon.Color = c.IconColor
if gtx.Queue == nil {
icon.Color = mulAlpha(icon.Color, 150)
icon.Color = f32color.MulAlpha(icon.Color, 150)
}
icon.Layout(gtx, unit.Px(float32(size)))
return layout.Dimensions{
widget/material/editor.go
+2 -1
View File
@@ -5,6 +5,7 @@ package material
import (
"image/color"
"gioui.org/internal/f32color"
"gioui.org/layout"
"gioui.org/op"
"gioui.org/op/paint"
@@ -56,7 +57,7 @@ func (e EditorStyle) Layout(gtx layout.Context) layout.Dimensions {
if e.Editor.Len() > 0 {
textColor := e.Color
if disabled {
textColor = mulAlpha(textColor, 150)
textColor = f32color.MulAlpha(textColor, 150)
}
paint.ColorOp{Color: textColor}.Add(gtx.Ops)
e.Editor.PaintText(gtx)
widget/material/progressbar.go
+3 -13
View File
@@ -7,6 +7,7 @@ import (
"image/color"
"gioui.org/f32"
"gioui.org/internal/f32color"
"gioui.org/layout"
"gioui.org/op/clip"
"gioui.org/op/paint"
@@ -58,7 +59,7 @@ func (p ProgressBarStyle) Layout(gtx layout.Context) layout.Dimensions {
return layout.Stack{Alignment: layout.W}.Layout(gtx,
layout.Stacked(func(gtx layout.Context) layout.Dimensions {
// Use a transparent equivalent of progress color.
bgCol := mulAlpha(p.Color, 150)
bgCol := f32color.MulAlpha(p.Color, 150)
return shader(progressBarWidth, bgCol)
}),
@@ -66,20 +67,9 @@ func (p ProgressBarStyle) Layout(gtx layout.Context) layout.Dimensions {
fillWidth := (progressBarWidth / 100) * float32(progress)
fillColor := p.Color
if gtx.Queue == nil {
fillColor = mulAlpha(fillColor, 200)
fillColor = f32color.MulAlpha(fillColor, 200)
}
return shader(fillWidth, fillColor)
}),
)
}
// mulAlpha scales all color components by alpha/255.
func mulAlpha(c color.RGBA, alpha uint8) color.RGBA {
a := uint16(alpha)
return color.RGBA{
A: uint8(uint16(c.A) * a / 255),
R: uint8(uint16(c.R) * a / 255),
G: uint8(uint16(c.G) * a / 255),
B: uint8(uint16(c.B) * a / 255),
}
}
widget/material/slider.go
+3 -2
View File
@@ -7,6 +7,7 @@ import (
"image/color"
"gioui.org/f32"
"gioui.org/internal/f32color"
"gioui.org/layout"
"gioui.org/op"
"gioui.org/op/clip"
@@ -55,7 +56,7 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
color := s.Color
if gtx.Queue == nil {
color = mulAlpha(color, 150)
color = f32color.MulAlpha(color, 150)
}
// Draw track before thumb.
@@ -80,7 +81,7 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
track.Min.X = thumbPos
track.Max.X = float32(size.X) - halfWidth
clip.RRect{Rect: track}.Add(gtx.Ops)
paint.ColorOp{Color: mulAlpha(color, 96)}.Add(gtx.Ops)
paint.ColorOp{Color: f32color.MulAlpha(color, 96)}.Add(gtx.Ops)
paint.PaintOp{Rect: track}.Add(gtx.Ops)
st.Pop()
widget/material/switch.go
+3 -2
View File
@@ -7,6 +7,7 @@ import (
"image/color"
"gioui.org/f32"
"gioui.org/internal/f32color"
"gioui.org/io/pointer"
"gioui.org/layout"
"gioui.org/op"
@@ -52,9 +53,9 @@ func (s SwitchStyle) Layout(gtx layout.Context) layout.Dimensions {
col = s.Color.Enabled
}
if gtx.Queue == nil {
col = mulAlpha(col, 150)
col = f32color.MulAlpha(col, 150)
}
trackColor := mulAlpha(col, 150)
trackColor := f32color.MulAlpha(col, 150)
op.Offset(f32.Point{Y: trackOff}).Add(gtx.Ops)
clip.RRect{
Rect: trackRect,