feat(photos): добавить пресеты кривой и починить переключение фото

- PCHIP для предпросмотра и серверного рендера
- пресеты всех каналов в профиле, импорт и экспорт
- мерж настроек auth без потери разделов
- сохранение вкладки и правок текущего фото при переключении

backend/internal/auth/handlers.go

@@ -4,7 +4,10 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"math"
 	"net/http"
+	"strings"
+	"unicode/utf8"
 
 	"github.com/gin-gonic/gin"
 
@@ -181,6 +184,9 @@ const (
 	maxLabelEntries       = 500
 	maxPreferenceKeyLen   = 128
 	maxPreferenceValueLen = 128
+	maxCurvePresets       = 100
+	maxCurvePresetNameLen = 64
+	maxCurvePresetPoints  = 16
 )
 
 type photoInfoPreferences struct {
@@ -188,33 +194,102 @@ type photoInfoPreferences struct {
 	Labels  map[string]string `json:"labels,omitempty"`
 }
 
+type curvePresetPoint struct {
+	X float64 `json:"x"`
+	Y float64 `json:"y"`
+}
+
+type curvePresetChannels struct {
+	RGB   []curvePresetPoint `json:"rgb"`
+	Red   []curvePresetPoint `json:"red"`
+	Green []curvePresetPoint `json:"green"`
+	Blue  []curvePresetPoint `json:"blue"`
+}
+
+type curvePreset struct {
+	Name     string              `json:"name"`
+	Channels curvePresetChannels `json:"channels"`
+}
+
 type preferencesPayload struct {
-	PhotoInfo *photoInfoPreferences `json:"photo_info,omitempty"`
+	PhotoInfo    *photoInfoPreferences `json:"photo_info,omitempty"`
+	CurvePresets *[]curvePreset        `json:"curve_presets,omitempty"`
+}
+
+// normalize trims preset names before they are validated and stored.
+func (p *preferencesPayload) normalize() {
+	if p.CurvePresets == nil {
+		return
+	}
+	for i := range *p.CurvePresets {
+		(*p.CurvePresets)[i].Name = strings.TrimSpace((*p.CurvePresets)[i].Name)
+	}
 }
 
 func (p preferencesPayload) validate() error {
 	pi := p.PhotoInfo
-	if pi == nil {
-		return nil
-	}
-	if len(pi.Visible) > maxVisibleAttrs {
-		return fmt.Errorf("too many visible attributes")
-	}
-	for _, k := range pi.Visible {
-		if k == "" || len(k) > maxPreferenceKeyLen {
-			return fmt.Errorf("invalid visible attribute key")
+	if pi != nil {
+		if len(pi.Visible) > maxVisibleAttrs {
+			return fmt.Errorf("too many visible attributes")
+		}
+		for _, k := range pi.Visible {
+			if k == "" || len(k) > maxPreferenceKeyLen {
+				return fmt.Errorf("invalid visible attribute key")
+			}
+		}
+		if len(pi.Labels) > maxLabelEntries {
+			return fmt.Errorf("too many label overrides")
+		}
+		for k, v := range pi.Labels {
+			if k == "" || len(k) > maxPreferenceKeyLen {
+				return fmt.Errorf("invalid label key")
+			}
+			if len(v) > maxPreferenceValueLen {
+				return fmt.Errorf("label value too long")
+			}
 		}
 	}
-	if len(pi.Labels) > maxLabelEntries {
-		return fmt.Errorf("too many label overrides")
+	if p.CurvePresets != nil {
+		return validateCurvePresets(*p.CurvePresets)
 	}
-	for k, v := range pi.Labels {
-		if k == "" || len(k) > maxPreferenceKeyLen {
-			return fmt.Errorf("invalid label key")
+	return nil
+}
+
+func validateCurvePresets(presets []curvePreset) error {
+	if len(presets) > maxCurvePresets {
+		return fmt.Errorf("too many curve presets")
+	}
+	names := make(map[string]struct{}, len(presets))
+	for _, preset := range presets {
+		if preset.Name == "" || utf8.RuneCountInString(preset.Name) > maxCurvePresetNameLen {
+			return fmt.Errorf("invalid curve preset name")
 		}
-		if len(v) > maxPreferenceValueLen {
-			return fmt.Errorf("label value too long")
+		channels := []struct {
+			name   string
+			points []curvePresetPoint
+		}{
+			{"rgb", preset.Channels.RGB},
+			{"red", preset.Channels.Red},
+			{"green", preset.Channels.Green},
+			{"blue", preset.Channels.Blue},
 		}
+		for _, channel := range channels {
+			if len(channel.points) < 2 || len(channel.points) > maxCurvePresetPoints {
+				return fmt.Errorf("invalid curve preset points for %s", channel.name)
+			}
+			for _, pt := range channel.points {
+				if math.IsNaN(pt.X) || math.IsNaN(pt.Y) || math.IsInf(pt.X, 0) || math.IsInf(pt.Y, 0) {
+					return fmt.Errorf("invalid curve preset point")
+				}
+				if pt.X < 0 || pt.X > 1 || pt.Y < 0 || pt.Y > 1 {
+					return fmt.Errorf("invalid curve preset point")
+				}
+			}
+		}
+		if _, dup := names[preset.Name]; dup {
+			return fmt.Errorf("duplicate curve preset name")
+		}
+		names[preset.Name] = struct{}{}
 	}
 	return nil
 }
@@ -230,18 +305,40 @@ func (h *Handler) UpdatePreferences(c *gin.Context) {
 		httpx.RespondError(c, httpx.BadRequest("invalid_preferences", "preferences must be a JSON object"))
 		return
 	}
+	payload.normalize()
 	if err := payload.validate(); err != nil {
 		httpx.RespondError(c, httpx.BadRequest("invalid_preferences", err.Error()))
 		return
 	}
-	raw, err := json.Marshal(payload)
+
+	ctx := c.Request.Context()
+	u, err := h.svc.store.GetUserByID(ctx, UserID(c))
 	if err != nil {
-		httpx.RespondError(c, httpx.BadRequest("invalid_preferences", "could not encode preferences"))
+		httpx.RespondError(c, httpx.Unauthorized("unauthorized", "user not found"))
 		return
 	}
-	if err := h.svc.store.UpdatePreferences(c.Request.Context(), UserID(c), raw); err != nil {
-		httpx.RespondError(c, err)
-		return
+	// Merge the submitted sections into the stored blob so saving one section
+	// never clears the others. Unknown keys are preserved.
+	merged := make(map[string]any, len(u.Preferences)+2)
+	for k, v := range u.Preferences {
+		merged[k] = v
 	}
-	c.JSON(http.StatusOK, gin.H{"preferences": payload})
+	if payload.PhotoInfo != nil {
+		merged["photo_info"] = payload.PhotoInfo
+	}
+	if payload.CurvePresets != nil {
+		merged["curve_presets"] = *payload.CurvePresets
+	}
+	if payload.PhotoInfo != nil || payload.CurvePresets != nil {
+		raw, err := json.Marshal(merged)
+		if err != nil {
+			httpx.RespondError(c, httpx.BadRequest("invalid_preferences", "could not encode preferences"))
+			return
+		}
+		if err := h.svc.store.UpdatePreferences(ctx, UserID(c), raw); err != nil {
+			httpx.RespondError(c, err)
+			return
+		}
+	}
+	c.JSON(http.StatusOK, gin.H{"preferences": merged})
 }

backend/internal/auth/handlers_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 
 	"github.com/gin-gonic/gin"
@@ -30,6 +31,7 @@ func newTestRouter(t *testing.T) *gin.Engine {
 	authed.PATCH("/auth/me", h.UpdateMe)
 	authed.POST("/auth/me/password", h.ChangePassword)
 	authed.POST("/auth/me/identifiers", h.AddIdentifier)
+	authed.PATCH("/auth/me/preferences", h.UpdatePreferences)
 	authed.DELETE("/auth/me", h.DeleteMe)
 	return r
 }
@@ -213,3 +215,215 @@ func TestDeleteMeHandler(t *testing.T) {
 		t.Fatalf("me after delete status = %d", rec.Code)
 	}
 }
+
+func curvePresetPayloadWith(name, channel string, points []map[string]float64) map[string]any {
+	linear := func() []map[string]float64 {
+		return []map[string]float64{
+			{"x": 0, "y": 0},
+			{"x": 1, "y": 1},
+		}
+	}
+	channels := map[string]any{
+		"rgb":   linear(),
+		"red":   linear(),
+		"green": linear(),
+		"blue":  linear(),
+	}
+	channels[channel] = points
+	return map[string]any{"name": name, "channels": channels}
+}
+
+func curvePresetPayload(name string) map[string]any {
+	return curvePresetPayloadWith(name, "rgb", []map[string]float64{
+		{"x": 0, "y": 0},
+		{"x": 1, "y": 0.8},
+	})
+}
+
+func decodePreferences(t *testing.T, rec *httptest.ResponseRecorder) map[string]any {
+	t.Helper()
+	var body struct {
+		Preferences map[string]any `json:"preferences"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Fatalf("decode preferences %s: %v", rec.Body.String(), err)
+	}
+	return body.Preferences
+}
+
+func TestUpdatePreferencesMergesSections(t *testing.T) {
+	r := newTestRouter(t)
+	reg := doJSON(r, http.MethodPost, "/auth/register", "", map[string]string{
+		"email": "prefs@test.local", "password": "password123", "name": "Prefs",
+	})
+	token := decodeAuth(t, reg).Tokens.AccessToken
+
+	rec := doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"photo_info": map[string]any{
+			"visible": []string{"camera"},
+			"labels":  map[string]string{"camera": "Камера"},
+		},
+	})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("save photo_info status = %d body = %s", rec.Code, rec.Body.String())
+	}
+
+	rec = doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"curve_presets": []any{curvePresetPayload("Мой")},
+	})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("save presets status = %d body = %s", rec.Code, rec.Body.String())
+	}
+	prefs := decodePreferences(t, rec)
+	if _, ok := prefs["photo_info"]; !ok {
+		t.Fatalf("photo_info lost after saving presets: %+v", prefs)
+	}
+	presets, ok := prefs["curve_presets"].([]any)
+	if !ok || len(presets) != 1 {
+		t.Fatalf("presets = %#v, want one", prefs["curve_presets"])
+	}
+
+	// Saving photo_info again must keep the presets.
+	rec = doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"photo_info": map[string]any{"visible": []string{"iso"}},
+	})
+	prefs = decodePreferences(t, rec)
+	if presets, ok := prefs["curve_presets"].([]any); !ok || len(presets) != 1 {
+		t.Fatalf("presets lost after saving photo_info: %+v", prefs)
+	}
+	info, _ := prefs["photo_info"].(map[string]any)
+	if visible, _ := info["visible"].([]any); len(visible) != 1 || visible[0] != "iso" {
+		t.Fatalf("photo_info not updated: %+v", prefs["photo_info"])
+	}
+
+	// The merged state is what GET /auth/me returns.
+	rec = doJSON(r, http.MethodGet, "/auth/me", token, nil)
+	var me struct {
+		Preferences map[string]any `json:"preferences"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &me); err != nil {
+		t.Fatalf("decode me: %v", err)
+	}
+	if _, ok := me.Preferences["photo_info"]; !ok {
+		t.Fatalf("me lost photo_info: %+v", me.Preferences)
+	}
+	if _, ok := me.Preferences["curve_presets"]; !ok {
+		t.Fatalf("me lost curve_presets: %+v", me.Preferences)
+	}
+
+	// An empty preset list clears only presets.
+	rec = doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"curve_presets": []any{},
+	})
+	prefs = decodePreferences(t, rec)
+	if presets, ok := prefs["curve_presets"].([]any); !ok || len(presets) != 0 {
+		t.Fatalf("presets not cleared: %+v", prefs["curve_presets"])
+	}
+	if _, ok := prefs["photo_info"]; !ok {
+		t.Fatalf("photo_info lost after clearing presets: %+v", prefs)
+	}
+
+	// Names are stored without surrounding whitespace.
+	rec = doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"curve_presets": []any{curvePresetPayload("  Мой  ")},
+	})
+	prefs = decodePreferences(t, rec)
+	presets = prefs["curve_presets"].([]any)
+	first, _ := presets[0].(map[string]any)
+	if first["name"] != "Мой" {
+		t.Fatalf("preset name = %#v, want trimmed", first["name"])
+	}
+}
+
+func TestPreferencesArePrivate(t *testing.T) {
+	r := newTestRouter(t)
+	first := decodeAuth(t, doJSON(r, http.MethodPost, "/auth/register", "", map[string]string{
+		"email": "private1@test.local", "password": "password123", "name": "One",
+	}))
+	second := decodeAuth(t, doJSON(r, http.MethodPost, "/auth/register", "", map[string]string{
+		"email": "private2@test.local", "password": "password123", "name": "Two",
+	}))
+
+	rec := doJSON(r, http.MethodPatch, "/auth/me/preferences", first.Tokens.AccessToken, map[string]any{
+		"curve_presets": []any{curvePresetPayload("Секрет")},
+	})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("save status = %d body = %s", rec.Code, rec.Body.String())
+	}
+
+	rec = doJSON(r, http.MethodGet, "/auth/me", second.Tokens.AccessToken, nil)
+	var me struct {
+		Preferences map[string]any `json:"preferences"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &me); err != nil {
+		t.Fatalf("decode me: %v", err)
+	}
+	if _, ok := me.Preferences["curve_presets"]; ok {
+		t.Fatalf("other user sees presets: %+v", me.Preferences)
+	}
+}
+
+func TestUpdatePreferencesRejectsInvalidCurvePresets(t *testing.T) {
+	r := newTestRouter(t)
+	reg := doJSON(r, http.MethodPost, "/auth/register", "", map[string]string{
+		"email": "invalidprefs@test.local", "password": "password123", "name": "Invalid",
+	})
+	token := decodeAuth(t, reg).Tokens.AccessToken
+
+	rec := doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+		"curve_presets": []any{curvePresetPayload("Хороший")},
+	})
+	if rec.Code != http.StatusOK {
+		t.Fatalf("seed status = %d body = %s", rec.Code, rec.Body.String())
+	}
+
+	manyPoints := make([]map[string]float64, 17)
+	for i := range manyPoints {
+		manyPoints[i] = map[string]float64{"x": float64(i) / 16, "y": float64(i) / 16}
+	}
+	tooMany := make([]any, 101)
+	for i := range tooMany {
+		tooMany[i] = curvePresetPayload("preset-" + string(rune('a'+i%26)) + strings.Repeat("x", i/26))
+	}
+
+	missingChannel := curvePresetPayload("bad")
+	delete(missingChannel["channels"].(map[string]any), "blue")
+
+	cases := []struct {
+		name    string
+		presets []any
+	}{
+		{"too long name", []any{curvePresetPayload(strings.Repeat("a", 65))}},
+		{"missing channel", []any{missingChannel}},
+		{"one point", []any{curvePresetPayloadWith("one", "red", []map[string]float64{
+			{"x": 0, "y": 0},
+		})}},
+		{"too many points", []any{curvePresetPayloadWith("many", "rgb", manyPoints)}},
+		{"x out of range", []any{curvePresetPayloadWith("range", "blue", []map[string]float64{
+			{"x": 1.1, "y": 0},
+			{"x": 1, "y": 1},
+		})}},
+		{"duplicate name", []any{curvePresetPayload("dup"), curvePresetPayload("dup")}},
+		{"too many presets", tooMany},
+	}
+	for _, tc := range cases {
+		rec := doJSON(r, http.MethodPatch, "/auth/me/preferences", token, map[string]any{
+			"curve_presets": tc.presets,
+		})
+		if rec.Code != http.StatusBadRequest {
+			t.Fatalf("%s status = %d body = %s", tc.name, rec.Code, rec.Body.String())
+		}
+	}
+
+	rec = doJSON(r, http.MethodGet, "/auth/me", token, nil)
+	var me struct {
+		Preferences map[string]any `json:"preferences"`
+	}
+	if err := json.Unmarshal(rec.Body.Bytes(), &me); err != nil {
+		t.Fatalf("decode me: %v", err)
+	}
+	presets, _ := me.Preferences["curve_presets"].([]any)
+	if len(presets) != 1 {
+		t.Fatalf("invalid requests changed presets: %+v", me.Preferences)
+	}
+}

backend/internal/e2e/curve_presets_test.go

@@ -0,0 +1,56 @@
+package e2e
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+)
+
+// Curve presets live in the user profile: they survive a round trip through
+// the metadata layer and are never visible to another user.
+func TestCurvePresetsPersistAndArePrivate(t *testing.T) {
+	ctx := context.Background()
+	st, closeDB := openStack(t, filepath.Join(t.TempDir(), "galo.db"), t.TempDir())
+	defer closeDB()
+
+	owner, _, err := st.auth.Register(ctx, "presets@test.local", "", "password123", "Owner")
+	if err != nil {
+		t.Fatalf("register owner: %v", err)
+	}
+	other, _, err := st.auth.Register(ctx, "otherpresets@test.local", "", "password123", "Other")
+	if err != nil {
+		t.Fatalf("register other: %v", err)
+	}
+
+	raw := []byte(`{"curve_presets":[{"name":"Мой контраст","channels":{"rgb":[{"x":0,"y":0},{"x":1,"y":0.9}],"red":[{"x":0,"y":0},{"x":1,"y":1}],"green":[{"x":0,"y":0},{"x":1,"y":1}],"blue":[{"x":0,"y":0},{"x":1,"y":1}]}}]}`)
+	if err := st.repos.Auth.UpdatePreferences(ctx, owner.ID, raw); err != nil {
+		t.Fatalf("update preferences: %v", err)
+	}
+
+	got, err := st.repos.Auth.GetUserByID(ctx, owner.ID)
+	if err != nil {
+		t.Fatalf("get owner: %v", err)
+	}
+	presets, ok := got.Preferences["curve_presets"].([]any)
+	if !ok || len(presets) != 1 {
+		t.Fatalf("presets not stored: %+v", got.Preferences)
+	}
+	preset, _ := presets[0].(map[string]any)
+	if preset["name"] != "Мой контраст" {
+		t.Fatalf("preset = %+v", preset)
+	}
+	channels, _ := preset["channels"].(map[string]any)
+	for _, channel := range []string{"rgb", "red", "green", "blue"} {
+		if points, ok := channels[channel].([]any); !ok || len(points) != 2 {
+			t.Fatalf("channel %s = %#v", channel, channels[channel])
+		}
+	}
+
+	otherUser, err := st.repos.Auth.GetUserByID(ctx, other.ID)
+	if err != nil {
+		t.Fatalf("get other: %v", err)
+	}
+	if _, ok := otherUser.Preferences["curve_presets"]; ok {
+		t.Fatalf("other user sees presets: %+v", otherUser.Preferences)
+	}
+}

backend/internal/photos/edit.go

@@ -317,8 +317,9 @@ func clampInt(v, min, max int) int {
 }
 
 // curveLUT builds a 256-entry lookup table from the control points of a
-// curve. The first and last points extend to the edges of the range, and the
-// values in between are interpolated linearly.
+// curve. The first and last points extend to the edges of the range as flat
+// shelves, and the values in between are interpolated with a monotone cubic
+// Hermite spline (PCHIP, Fritsch–Carlson).
 func curveLUT(points []CurvePoint) [256]uint8 {
 	var lut [256]uint8
 	pts := normalizeCurve(points)
@@ -328,16 +329,71 @@ func curveLUT(points []CurvePoint) [256]uint8 {
 		}
 		return lut
 	}
+	tangents := curveTangents(pts)
 	for i := 0; i < 256; i++ {
 		x := float64(i) / 255
-		lut[i] = uint8(math.Round(clamp01(curveEval(pts, x)) * 255))
+		lut[i] = uint8(math.Round(clamp01(curveEvalWithTangents(pts, tangents, x)) * 255))
 	}
 	return lut
 }
 
-// curveEval evaluates the curve at x using linear interpolation between the
-// surrounding control points.
+// curveTangents returns the PCHIP slopes at the control points. Interior
+// tangents are weighted harmonic means of the neighbouring slopes; endpoint
+// tangents use the one-sided three-point formula with the Fritsch–Carlson
+// shape-preserving clamp.
+func curveTangents(points []CurvePoint) []float64 {
+	n := len(points)
+	if n < 2 {
+		return nil
+	}
+	h := make([]float64, n-1)
+	delta := make([]float64, n-1)
+	for i := 0; i < n-1; i++ {
+		h[i] = points[i+1].X - points[i].X
+		delta[i] = (points[i+1].Y - points[i].Y) / h[i]
+	}
+	m := make([]float64, n)
+	if n == 2 {
+		m[0] = delta[0]
+		m[1] = delta[0]
+		return m
+	}
+	m[0] = endpointTangent(h[0], h[1], delta[0], delta[1])
+	m[n-1] = endpointTangent(h[n-2], h[n-3], delta[n-2], delta[n-3])
+	for i := 1; i < n-1; i++ {
+		if delta[i-1]*delta[i] <= 0 {
+			m[i] = 0
+			continue
+		}
+		w1 := 2*h[i] + h[i-1]
+		w2 := h[i] + 2*h[i-1]
+		m[i] = (w1 + w2) / (w1/delta[i-1] + w2/delta[i])
+	}
+	return m
+}
+
+// endpointTangent is the one-sided endpoint slope of the PCHIP spline.
+func endpointTangent(h0, h1, d0, d1 float64) float64 {
+	m := ((2*h0+h1)*d0 - h0*d1) / (h0 + h1)
+	if m*d0 <= 0 {
+		return 0
+	}
+	if d0*d1 < 0 && math.Abs(m) > math.Abs(3*d0) {
+		return 3 * d0
+	}
+	return m
+}
+
+// curveEval evaluates the curve at x with a monotone cubic Hermite spline.
+// Outside the first and last points the value is constant.
 func curveEval(points []CurvePoint, x float64) float64 {
+	if len(points) < 2 {
+		return x
+	}
+	return curveEvalWithTangents(points, curveTangents(points), x)
+}
+
+func curveEvalWithTangents(points []CurvePoint, tangents []float64, x float64) float64 {
 	if x <= points[0].X {
 		return points[0].Y
 	}
@@ -345,19 +401,23 @@ func curveEval(points []CurvePoint, x float64) float64 {
 	if x >= last.X {
 		return last.Y
 	}
-	for i := 1; i < len(points); i++ {
-		if x > points[i].X {
-			continue
-		}
-		x0, y0 := points[i-1].X, points[i-1].Y
-		x1, y1 := points[i].X, points[i].Y
-		if x1-x0 < 1e-9 {
-			return y1
-		}
-		t := (x - x0) / (x1 - x0)
-		return y0 + t*(y1-y0)
+	i := 1
+	for i < len(points)-1 && x > points[i].X {
+		i++
 	}
-	return last.Y
+	p0, p1 := points[i-1], points[i]
+	h := p1.X - p0.X
+	if h < 1e-9 {
+		return p1.Y
+	}
+	t := (x - p0.X) / h
+	t2 := t * t
+	t3 := t2 * t
+	h00 := 2*t3 - 3*t2 + 1
+	h10 := t3 - 2*t2 + t
+	h01 := -2*t3 + 3*t2
+	h11 := t3 - t2
+	return h00*p0.Y + h10*h*tangents[i-1] + h01*p1.Y + h11*h*tangents[i]
 }
 
 // lightAdjuster holds the precomputed factors of the light adjustments. The

backend/internal/photos/edit_test.go

@@ -91,6 +91,70 @@ func TestCurveLUTSteepens(t *testing.T) {
 	}
 }
 
+// The client builds the same 256-entry LUT (frontend/src/lib/edit.ts). The
+// hard-coded samples keep the Go and TypeScript implementations in sync.
+func TestCurveLUTMatchesClient(t *testing.T) {
+	samples := []int{0, 32, 64, 128, 192, 224, 255}
+	cases := []struct {
+		name   string
+		points []CurvePoint
+		want   []int
+	}{
+		{"linear", []CurvePoint{{0, 0}, {1, 1}}, []int{0, 32, 64, 128, 192, 224, 255}},
+		{
+			"medium",
+			[]CurvePoint{{0, 0}, {0.25, 0.2}, {0.5, 0.5}, {0.75, 0.8}, {1, 1}},
+			[]int{0, 23, 51, 128, 205, 233, 255},
+		},
+		{
+			"strong",
+			[]CurvePoint{{0, 0}, {0.2, 0.12}, {0.5, 0.5}, {0.8, 0.88}, {1, 1}},
+			[]int{0, 17, 43, 128, 213, 239, 255},
+		},
+		{
+			"inner",
+			[]CurvePoint{{0.1, 0.05}, {0.4, 0.3}, {0.9, 0.95}},
+			[]int{13, 17, 42, 104, 186, 234, 242},
+		},
+	}
+	for _, tc := range cases {
+		lut := curveLUT(tc.points)
+		for i, index := range samples {
+			if int(lut[index]) != tc.want[i] {
+				t.Fatalf("%s lut[%d] = %d, want %d", tc.name, index, lut[index], tc.want[i])
+			}
+		}
+	}
+}
+
+func TestCurveLUTIsMonotone(t *testing.T) {
+	for _, points := range [][]CurvePoint{
+		{{0, 0}, {0.25, 0.2}, {0.5, 0.5}, {0.75, 0.8}, {1, 1}},
+		{{0, 0}, {0.2, 0.12}, {0.5, 0.5}, {0.8, 0.88}, {1, 1}},
+	} {
+		lut := curveLUT(points)
+		for i := 1; i < len(lut); i++ {
+			if lut[i] < lut[i-1] {
+				t.Fatalf("lut[%d] = %d < lut[%d] = %d", i, lut[i], i-1, lut[i-1])
+			}
+		}
+	}
+}
+
+func TestCurveLUTFlatOutsideEndpoints(t *testing.T) {
+	lut := curveLUT([]CurvePoint{{0.1, 0.05}, {0.4, 0.3}, {0.9, 0.95}})
+	for i := 0; i <= int(math.Floor(0.1*255)); i++ {
+		if lut[i] != 13 {
+			t.Fatalf("lut[%d] = %d, want flat 13", i, lut[i])
+		}
+	}
+	for i := 230; i < len(lut); i++ {
+		if lut[i] != 242 {
+			t.Fatalf("lut[%d] = %d, want flat 242", i, lut[i])
+		}
+	}
+}
+
 func TestApplyLightBrightensAndKeepsSource(t *testing.T) {
 	src := image.NewNRGBA(image.Rect(0, 0, 2, 2))
 	for i := range src.Pix {