ds-galo/backend/internal/photos/edit_render.go

package photos

import (
	"bytes"
	"image"
	"runtime"
	"sync"

	"github.com/disintegration/imaging"
	"github.com/gen2brain/webp"
)

// Object roles holding the non-destructive edited version of a photo. They
// mirror the base roles and are bound in addition to them.
const (
	RoleEdit        = "edit"
	RoleEditThumb   = "edit_thumb"
	RoleEditMedium  = "edit_medium"
	RoleEditPreview = "edit_preview"
)

// EditRoles lists the roles of the edited version. The edited version belongs
// to the photo whose edits produced it, so copies of that photo never share
// these roles.
func EditRoles() []string {
	return []string{RoleEdit, RoleEditThumb, RoleEditMedium, RoleEditPreview}
}

// IsEditRole reports whether the role belongs to the edited version.
func IsEditRole(role string) bool {
	switch role {
	case RoleEdit, RoleEditThumb, RoleEditMedium, RoleEditPreview:
		return true
	}
	return false
}

// applyLight renders the light adjustments into a copy of the image. The
// original pixels are never modified in place.
func applyLight(src image.Image, p LightParams) *image.NRGBA {
	// Clone returns a fresh NRGBA copy, so the source stays untouched.
	dst := imaging.Clone(src)

	master := curveLUT(p.Curve.RGB)
	red := curveLUT(p.Curve.Red)
	green := curveLUT(p.Curve.Green)
	blue := curveLUT(p.Curve.Blue)
	adj := newLightAdjuster(p)

	rows := dst.Rect.Dy()
	workers := runtime.GOMAXPROCS(0)
	if workers > rows {
		workers = rows
	}
	if workers <= 1 {
		applyLightRows(dst, 0, rows, adj, &master, &red, &green, &blue)
		return dst
	}
	// Рендер больших фото идёт по строкам параллельно.
	chunk := (rows + workers - 1) / workers
	var wg sync.WaitGroup
	for from := 0; from < rows; from += chunk {
		to := from + chunk
		if to > rows {
			to = rows
		}
		wg.Add(1)
		go func(from, to int) {
			defer wg.Done()
			applyLightRows(dst, from, to, adj, &master, &red, &green, &blue)
		}(from, to)
	}
	wg.Wait()
	return dst
}

// applyLightRows applies the adjustments to the given range of rows.
func applyLightRows(dst *image.NRGBA, from, to int, adj lightAdjuster, master, red, green, blue *[256]uint8) {
	width := dst.Rect.Dx()
	for y := from; y < to; y++ {
		row := dst.Pix[y*dst.Stride : y*dst.Stride+width*4]
		for i := 0; i+3 < len(row); i += 4 {
			if row[i+3] == 0 {
				continue
			}
			row[i] = uint8(adj.apply(float64(row[i]), master, red))
			row[i+1] = uint8(adj.apply(float64(row[i+1]), master, green))
			row[i+2] = uint8(adj.apply(float64(row[i+2]), master, blue))
		}
	}
}

// decodeAndAdjust decodes the original and applies the light adjustments to
// it, so the variants and the full-size version share one decode.
func decodeAndAdjust(data []byte, p EditParams) (*image.NRGBA, error) {
	img, err := imaging.Decode(bytes.NewReader(data), imaging.AutoOrientation(true))
	if err != nil {
		return nil, err
	}
	return applyLight(img, p.Light), nil
}

// encodeEditedVariants renders the grid variants of an edited photo. They
// mirror the base ones, so the grid and the viewer can switch to them
// transparently.
func encodeEditedVariants(edited *image.NRGBA) (thumb, medium, preview []byte, err error) {
	thumbImg := imaging.Fill(edited, 200, 200, imaging.Center, imaging.Lanczos)
	mediumImg := imaging.Fill(edited, 800, 800, imaging.Center, imaging.Lanczos)
	previewImg := imaging.Fit(edited, 1200, 1200, imaging.Lanczos)

	opts := webp.Options{Quality: 82}
	var buf bytes.Buffer
	if err := webp.Encode(&buf, thumbImg, opts); err != nil {
		return nil, nil, nil, err
	}
	thumb = buf.Bytes()

	buf.Reset()
	if err := webp.Encode(&buf, mediumImg, opts); err != nil {
		return nil, nil, nil, err
	}
	medium = buf.Bytes()

	buf.Reset()
	if err := webp.Encode(&buf, previewImg, opts); err != nil {
		return nil, nil, nil, err
	}
	preview = buf.Bytes()
	return thumb, medium, preview, nil
}

// encodeEdited renders an edited image part as WebP.
func encodeEdited(edited *image.NRGBA) ([]byte, error) {
	var buf bytes.Buffer
	if err := webp.Encode(&buf, edited, webp.Options{Quality: 82}); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}