1 files changed, 36 insertions, 0 deletions
diff --git a/internal/comic/pageframe.go b/internal/comic/pageframe.go
new file mode 100644
index 0000000..82ab363
--- /dev/null
+++ b/internal/comic/pageframe.go
@@ -0,0 +1,36 @@
+package comic
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// DescribePageFrame returns human-readable page shape text for image prompts,
+// derived from a Gemini-style aspect ratio such as "16:9" or "2:3".
+func DescribePageFrame(aspectRatio string) string {
+	aspectRatio = strings.TrimSpace(aspectRatio)
+	if aspectRatio == "" {
+		aspectRatio = comicPageAspectRatio
+	}
+	parts := strings.Split(aspectRatio, ":")
+	if len(parts) != 2 {
+		return fmt.Sprintf("%s format", aspectRatio)
+	}
+	w, errW := strconv.Atoi(strings.TrimSpace(parts[0]))
+	h, errH := strconv.Atoi(strings.TrimSpace(parts[1]))
+	if errW != nil || errH != nil || w <= 0 || h <= 0 {
+		return fmt.Sprintf("%s format", aspectRatio)
+	}
+	switch {
+	case w < h:
+		if w == 3 && h == 4 {
+			return "portrait 3:4 format (ISO A4–class sheet: 210×297 mm target; image API uses 3:4 as the closest standard ratio)"
+		}
+		return fmt.Sprintf("portrait %s format (tall comic book page proportions)", aspectRatio)
+	case w > h:
+		return fmt.Sprintf("landscape %s format (widescreen)", aspectRatio)
+	default:
+		return fmt.Sprintf("square %s format", aspectRatio)
+	}
+}