// mix takes two colors and optional weight (50% assumed). mix evaluates the
// difference of alphas and factors this into the weight calculations
// For details see: http://sass-lang.com/documentation/Sass/Script/Functions.html#mix-instance_method
func mix(call *ast.CallExpr, args ...*ast.BasicLit) (*ast.BasicLit, error) {
wt, err := strconv.ParseFloat(args[2].Value, 8)
// Parse percentage ie. 50%
if err != nil {
var i float64
_, err := fmt.Sscanf(args[2].Value, "%f%%", &i)
if err != nil {
log.Fatal(err)
}
wt = i / 100
}
c1, err := ast.ColorFromHexString(args[0].Value)
if err != nil {
return nil, fmt.Errorf("failed to read hex string %s: %s",
args[0].Value, err)
}
c2, err := ast.ColorFromHexString(args[1].Value)
if err != nil {
return nil, fmt.Errorf("failed to read hex string %s: %s",
args[1].Value, err)
}
var r, g, b, a float64
a1, a2 := float64(c1.A)/100, float64(c2.A)/100
w := wt*2 - 1
a = a1 - a2
var w1 float64
// if w*a == -1, weight is w
if w*a == -1 {
w1 = w
} else {
w1 = (w + a) / (1 + w*a)
}
w1 = (w1 + 1) / 2
w2 := 1 - w1
r = w1*float64(c1.R) + w2*float64(c2.R)
g = w1*float64(c1.G) + w2*float64(c2.G)
b = w1*float64(c1.B) + w2*float64(c2.B)
alpha := (float64(c1.A) + float64(c2.A)) / 2
ret := color.RGBA{
R: uint8(round(r, 0)),
G: uint8(round(g, 0)),
B: uint8(round(b, 0)),
A: uint8(round(alpha, 2)),
}
return colorOutput(ret, call.Args[0]), nil
}
func invert(call *ast.CallExpr, args ...*ast.BasicLit) (*ast.BasicLit, error) {
val := args[0].Value
c, err := ast.ColorFromHexString(val)
if err != nil {
return nil, fmt.Errorf("invert failed to parse argument %s; %s", val, err)
}
c.R = 255 - c.R
c.G = 255 - c.G
c.B = 255 - c.B
return colorOutput(c, call.Args[0]), nil
}
func parseColors(args []*ast.BasicLit) (color.RGBA, error) {
ints := make([]uint8, 4)
var ret color.RGBA
var u uint8
for i := range args {
v := args[i]
switch v.Kind {
case token.FLOAT:
f, err := strconv.ParseFloat(args[i].Value, 8)
if err != nil {
return ret, err
}
// Has to be alpha, or bust
u = uint8(f * 100)
case token.INT:
i, err := strconv.Atoi(v.Value)
if err != nil {
return ret, err
}
u = uint8(i)
case token.COLOR:
if i != 0 {
return ret, fmt.Errorf("hex is only allowed as the first argumetn found: % #v", v)
}
var err error
ret, err = ast.ColorFromHexString(v.Value)
if err != nil {
return ret, err
}
// This is only allowed as the first argument
i = i + 2
default:
log.Fatalf("unsupported kind %s % #v\n", v.Kind, v)
}
ints[i] = u
}
if ints[0] > 0 {
ret.R = ints[0]
}
if ints[1] > 0 {
ret.G = ints[1]
}
if ints[2] > 0 {
ret.B = ints[2]
}
if ints[3] > 0 {
ret.A = ints[3]
}
return ret, nil
}