topfans/backend/gateway/service/compositor/finish.go

package compositor

import (
	"image"
	"math"
)

// DrawMetallicSheen 绘制对角金属反光梯度（screen 混合）
func DrawMetallicSheen(dst *image.NRGBA, cfg GratingConfig) {
	cw := dst.Bounds().Dx()
	ch := dst.Bounds().Dy()

	deg := cfg.SheenBandAngle
	if deg == 0 {
		deg = 135
	}
	// 与色带垂直方向
	deg += 90
	rad := deg * math.Pi / 180

	diag := math.Sqrt(float64(cw*cw + ch*ch))
	cx := float64(cw) / 2
	cy := float64(ch) / 2
	x0 := cx - math.Cos(rad)*diag/2
	y0 := cy - math.Sin(rad)*diag/2
	x1 := cx + math.Cos(rad)*diag/2
	y1 := cy + math.Sin(rad)*diag/2

	alpha := 0.10 // 调低金属反光强度，让人物更清晰

	for y := 0; y < ch; y++ {
		for x := 0; x < cw; x++ {
			// 计算投影位置 0-1
			t := projectPointOnLine(float64(x), float64(y), x0, y0, x1, y1)

			// 中间带高亮，两端透明
			var brightness float64
			if t > 0.30 && t < 0.70 {
				// 高亮区域：余弦波
				brightness = math.Cos((t-0.50)/0.20*math.Pi) * 0.5
				if brightness < 0 {
					brightness = 0
				}
			}

			if brightness < 0.01 {
				continue
			}

			applyScreenPixel(dst, x, y, 220.0/255.0, 230.0/255.0, 240.0/255.0, brightness*alpha)
		}
	}
}

func projectPointOnLine(px, py, lx0, ly0, lx1, ly1 float64) float64 {
	dx := lx1 - lx0
	dy := ly1 - ly0
	lenSq := dx*dx + dy*dy
	if lenSq < 0.001 {
		return 0.5
	}
	t := ((px-lx0)*dx + (py-ly0)*dy) / lenSq
	return clamp01(t)
}

// DrawFrostMatte 磨砂哑光层
func DrawFrostMatte(dst *image.NRGBA, variantIndex int) {
	cw := dst.Bounds().Dx()
	ch := dst.Bounds().Dy()

	frost := 0.04 // 调低磨砂强度，真实镭射卡没有雾面效果

	// 颗粒噪声
	seed := variantIndex*1201 + 77
	n := int(500 + frost*7500)

	for k := 0; k < n; k++ {
		seed = (seed*9301 + 49297) % 233280
		x := seed % cw
		seed = (seed*9301 + 49297) % 233280
		y := seed % ch

		seed = (seed*9301 + 49297) % 233280
		v := 190 + seed%65
		a := 0.022 + float64(seed%55)/1000.0

		idx := dst.PixOffset(x, y)

		// soft-light 混合简化
		factor := a * (0.35 + frost*0.25)
		dst.Pix[idx] = uint8(clamp01(float64(dst.Pix[idx])/255.0+float64(v)*factor/255.0) * 255)
		dst.Pix[idx+1] = uint8(clamp01(float64(dst.Pix[idx+1])/255.0+float64(v)*factor/255.0) * 255)
		dst.Pix[idx+2] = uint8(clamp01(float64(dst.Pix[idx+2])/255.0+float64(v+6)*factor/255.0) * 255)
	}
}

// DrawFilmGrain 胶片颗粒
func DrawFilmGrain(dst *image.NRGBA, variantIndex int) {
	cw := dst.Bounds().Dx()
	ch := dst.Bounds().Dy()
	maxDots := 8

	seed := variantIndex*313 + 17
	for i := 0; i < maxDots; i++ {
		seed = (seed*1103515245 + 12345) & 0x7fffffff
		fx := float64(seed) / float64(0x7fffffff) * float64(cw)
		seed = (seed*1103515245 + 12345) & 0x7fffffff
		fy := float64(seed) / float64(0x7fffffff) * float64(ch)

		x := int(fx)
		y := int(fy)
		if x < 0 || x >= cw || y < 0 || y >= ch {
			continue
		}

		seed = (seed*1103515245 + 12345) & 0x7fffffff
		radius := float64(seed)/float64(0x7fffffff)*1.5 + 0.3
		alpha := 0.08 + float64(seed%12)/100.0

		drawSoftDot(dst, x, y, int(radius), alpha)
	}
}

func drawSoftDot(dst *image.NRGBA, cx, cy, radius int, alpha float64) {
	for dy := -radius; dy <= radius; dy++ {
		for dx := -radius; dx <= radius; dx++ {
			if dx*dx+dy*dy > radius*radius {
				continue
			}
			px, py := cx+dx, cy+dy
			if px < 0 || px >= dst.Bounds().Dx() || py < 0 || py >= dst.Bounds().Dy() {
				continue
			}

			dist := math.Sqrt(float64(dx*dx + dy*dy))
			fade := 1 - dist/float64(radius)
			idx := dst.PixOffset(px, py)

			sc := alpha * fade
			dst.Pix[idx] = uint8(clamp01(float64(dst.Pix[idx])/255.0+1.0*sc) * 255)
			dst.Pix[idx+1] = uint8(clamp01(float64(dst.Pix[idx+1])/255.0+1.0*sc) * 255)
			dst.Pix[idx+2] = uint8(clamp01(float64(dst.Pix[idx+2])/255.0+1.0*sc) * 255)
		}
	}
}

// DrawGratingFinish 光栅 finish：颗粒 + 磨砂
func DrawGratingFinish(dst *image.NRGBA, variantIndex int) {
	DrawFilmGrain(dst, variantIndex)
	DrawFrostMatte(dst, variantIndex)
}