feat(image): preserve transparency for alpha images end to end

Skip WebP re-encoding for PNG/AVIF/BMP uploads and any bitmap that actually contains alpha, tag transparency-capable canvas uploads with the transparent-image tone, and detect alpha in merged layers so the composed node keeps a transparent tone. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-07-08 01:54:32 +08:00
parent bd327e8564
commit 07aa33d30e
4 changed files with 141 additions and 3 deletions
@@ -129,6 +129,71 @@ func TestMergeLayersFlattensTextOverImage(t *testing.T) {
 	}
 }

+func TestMergeLayersPreservesTransparentPixels(t *testing.T) {
+	ctx := context.Background()
+	repo := memory.NewProjectRepository()
+	service := NewDesignService(repo, nil, nil, nil, nil)
+	transparentLayer := image.NewNRGBA(image.Rect(0, 0, 3, 2))
+	transparentLayer.SetNRGBA(1, 0, color.NRGBA{R: 255, A: 255})
+	project := design.Project{
+		ID:        "project-merge-transparent",
+		Title:     "Merge transparent",
+		Status:    design.StatusReady,
+		UpdatedAt: time.Now(),
+		Nodes: []design.Node{
+			{
+				ID:      "transparent",
+				Type:    design.NodeTypeImage,
+				Title:   "Transparent",
+				X:       0,
+				Y:       0,
+				Width:   3,
+				Height:  2,
+				Content: testPNGDataURLFromImage(transparentLayer),
+				Status:  "success",
+			},
+			{
+				ID:      "blue",
+				Type:    design.NodeTypeImage,
+				Title:   "Blue",
+				X:       2,
+				Y:       1,
+				Width:   1,
+				Height:  1,
+				Content: testPNGDataURL(color.NRGBA{B: 255, A: 255}, 1, 1),
+				Status:  "success",
+			},
+		},
+	}
+	if err := repo.Save(ctx, project); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := service.MergeLayers(ctx, project.ID, []string{"transparent", "blue"}, "Transparent merge"); err != nil {
+		t.Fatal(err)
+	}
+
+	merged := waitForMergedProject(t, repo, project.ID)
+	node := merged.Nodes[0]
+	if node.Tone != "transparent-image" {
+		t.Fatalf("expected transparent merged image tone, got %q", node.Tone)
+	}
+	imageData, _, _, ok, err := decodeDataImage(node.Content)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Fatalf("expected merged content data URL, got %s", node.Content)
+	}
+	decoded, err := png.Decode(bytes.NewReader(imageData))
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertPixel(t, decoded, 0, 0, color.NRGBA{})
+	assertPixel(t, decoded, 1, 0, color.NRGBA{R: 255, A: 255})
+	assertPixel(t, decoded, 2, 1, color.NRGBA{B: 255, A: 255})
+}
+
 func waitForMergedProject(t *testing.T, repo design.Repository, projectID string) design.Project {
 	t.Helper()
 	deadline := time.After(2 * time.Second)
@@ -160,6 +225,10 @@ func testPNGDataURL(fill color.NRGBA, width int, height int) string {
 			img.SetNRGBA(x, y, fill)
 		}
 	}
+	return testPNGDataURLFromImage(img)
+}
+
+func testPNGDataURLFromImage(img image.Image) string {
 	var buf bytes.Buffer
 	if err := png.Encode(&buf, img); err != nil {
 		panic(err)