1package imaging
2
3import (
4	"image"
5	"math"
6	"runtime"
7	"sync"
8)
9
10// parallel processes the data in separate goroutines.
11func parallel(start, stop int, fn func(<-chan int)) {
12	count := stop - start
13	if count < 1 {
14		return
15	}
16
17	procs := runtime.GOMAXPROCS(0)
18	if procs > count {
19		procs = count
20	}
21
22	c := make(chan int, count)
23	for i := start; i < stop; i++ {
24		c <- i
25	}
26	close(c)
27
28	var wg sync.WaitGroup
29	for i := 0; i < procs; i++ {
30		wg.Add(1)
31		go func() {
32			defer wg.Done()
33			fn(c)
34		}()
35	}
36	wg.Wait()
37}
38
39// absint returns the absolute value of i.
40func absint(i int) int {
41	if i < 0 {
42		return -i
43	}
44	return i
45}
46
47// clamp rounds and clamps float64 value to fit into uint8.
48func clamp(x float64) uint8 {
49	v := int64(x + 0.5)
50	if v > 255 {
51		return 255
52	}
53	if v > 0 {
54		return uint8(v)
55	}
56	return 0
57}
58
59func reverse(pix []uint8) {
60	if len(pix) <= 4 {
61		return
62	}
63	i := 0
64	j := len(pix) - 4
65	for i < j {
66		pi := pix[i : i+4 : i+4]
67		pj := pix[j : j+4 : j+4]
68		pi[0], pj[0] = pj[0], pi[0]
69		pi[1], pj[1] = pj[1], pi[1]
70		pi[2], pj[2] = pj[2], pi[2]
71		pi[3], pj[3] = pj[3], pi[3]
72		i += 4
73		j -= 4
74	}
75}
76
77func toNRGBA(img image.Image) *image.NRGBA {
78	if img, ok := img.(*image.NRGBA); ok {
79		return &image.NRGBA{
80			Pix:    img.Pix,
81			Stride: img.Stride,
82			Rect:   img.Rect.Sub(img.Rect.Min),
83		}
84	}
85	return Clone(img)
86}
87
88// rgbToHSL converts a color from RGB to HSL.
89func rgbToHSL(r, g, b uint8) (float64, float64, float64) {
90	rr := float64(r) / 255
91	gg := float64(g) / 255
92	bb := float64(b) / 255
93
94	max := math.Max(rr, math.Max(gg, bb))
95	min := math.Min(rr, math.Min(gg, bb))
96
97	l := (max + min) / 2
98
99	if max == min {
100		return 0, 0, l
101	}
102
103	var h, s float64
104	d := max - min
105	if l > 0.5 {
106		s = d / (2 - max - min)
107	} else {
108		s = d / (max + min)
109	}
110
111	switch max {
112	case rr:
113		h = (gg - bb) / d
114		if g < b {
115			h += 6
116		}
117	case gg:
118		h = (bb-rr)/d + 2
119	case bb:
120		h = (rr-gg)/d + 4
121	}
122	h /= 6
123
124	return h, s, l
125}
126
127// hslToRGB converts a color from HSL to RGB.
128func hslToRGB(h, s, l float64) (uint8, uint8, uint8) {
129	var r, g, b float64
130	if s == 0 {
131		v := clamp(l * 255)
132		return v, v, v
133	}
134
135	var q float64
136	if l < 0.5 {
137		q = l * (1 + s)
138	} else {
139		q = l + s - l*s
140	}
141	p := 2*l - q
142
143	r = hueToRGB(p, q, h+1/3.0)
144	g = hueToRGB(p, q, h)
145	b = hueToRGB(p, q, h-1/3.0)
146
147	return clamp(r * 255), clamp(g * 255), clamp(b * 255)
148}
149
150func hueToRGB(p, q, t float64) float64 {
151	if t < 0 {
152		t++
153	}
154	if t > 1 {
155		t--
156	}
157	if t < 1/6.0 {
158		return p + (q-p)*6*t
159	}
160	if t < 1/2.0 {
161		return q
162	}
163	if t < 2/3.0 {
164		return p + (q-p)*(2/3.0-t)*6
165	}
166	return p
167}
168