61 lines
1.5 KiB
Go
61 lines
1.5 KiB
Go
package helper
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import (
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"image/color"
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"iter"
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)
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// Enum iterates over a sparse sample of the RGBA colour space.
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//
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// If alpha is true, the colours will include transparency,
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// otherwise the returned colours will be fully opaque.
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//
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// If slow is false, an even smaller number of samples will be returned
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// making this suitable for use in a nested loop.
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//
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// alpha=true slow=true: 87481 samples.
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// alpha=false slow=true: 140608 samples.
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// alpha=true slow=false: 649 samples.
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// alpha=false slow=false: 216 samples.
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func Enum(alpha, slow bool) iter.Seq[color.RGBA64] {
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var aStart, aStep, cDiv uint32
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switch {
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case alpha && slow:
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aStart, aStep, cDiv = 0, 0xffff/15, 17
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case alpha: // alpha && !slow
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aStart, aStep, cDiv = 0, 0xffff/3, 5
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case slow: // !alpha && slow
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aStart, aStep, cDiv = 0xffff, 1, 51
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default: // !alpha && !slow
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aStart, aStep, cDiv = 0xffff, 1, 5
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}
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return func(yield func(color.RGBA64) bool) {
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for a := aStart; a <= 0xffff; a += aStep {
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cStep := max(1, a/cDiv)
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for b := uint32(0); b <= a; b += cStep {
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for g := uint32(0); g <= a; g += cStep {
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for r := uint32(0); r <= a; r += cStep {
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if !yield(color.RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}) {
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return
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}
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}
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}
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}
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}
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}
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}
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// EnumColor is identical to [Enum], but invokes a [color.Model] to return a concrete colour type.
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func EnumColor[C color.Color](alpha, slow bool, m color.Model) iter.Seq[C] {
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return func(yield func(C) bool) {
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for rgba := range Enum(alpha, slow) {
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if !yield(m.Convert(rgba).(C)) {
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return
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}
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}
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}
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}
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