update backend to support rotating and resizing about the centerpoint

app/core/src/main/java/stirling/software/SPDF/controller/api/misc/StampController.java

@@ -239,34 +239,54 @@ public class StampController {
 
         PDRectangle pageSize = page.getMediaBox();
         float x, y;
-
-        if (overrideX >= 0 && overrideY >= 0) {
-            // Use override values if provided
-            x = overrideX;
-            y = overrideY;
-        } else {
-            x = calculatePositionX(pageSize, position, fontSize, font, fontSize, stampText, margin);
-            y =
-                    calculatePositionY(
-                            pageSize, position, calculateTextCapHeight(font, fontSize), margin);
-        }
         // Split the stampText into multiple lines
-        String[] lines = stampText.split("\\\\n");
+        String[] lines = stampText.split("\\r?\\n|\\\\n");
 
         // Calculate dynamic line height based on font ascent and descent
         float ascent = font.getFontDescriptor().getAscent();
         float descent = font.getFontDescriptor().getDescent();
         float lineHeight = ((ascent - descent) / 1000) * fontSize;
 
+        // Compute a single pivot for the entire text block to avoid line-by-line wobble
+        float capHeight = calculateTextCapHeight(font, fontSize);
+        float blockHeight = Math.max(lineHeight, lineHeight * Math.max(1, lines.length));
+        float maxWidth = 0f;
+        for (String ln : lines) {
+            maxWidth = Math.max(maxWidth, calculateTextWidth(ln, font, fontSize));
+        }
+
+        if (overrideX >= 0 && overrideY >= 0) {
+            // Use override values if provided
+            x = overrideX;
+            y = overrideY;
+        } else {
+            // Base positioning on the true multi-line block size
+            x = calculatePositionX(pageSize, position, maxWidth, null, 0, null, margin);
+            y = calculatePositionY(pageSize, position, blockHeight, margin);
+        }
+
+        // After anchoring the block, draw from the top line downward
+        float adjustedX = x;
+        float adjustedY = y;
+        float pivotX = adjustedX + maxWidth / 2f;
+        float pivotY = adjustedY + blockHeight / 2f;
+
+        // Apply rotation about the block center at the graphics state level
+        contentStream.saveGraphicsState();
+        contentStream.transform(Matrix.getTranslateInstance(pivotX, pivotY));
+        contentStream.transform(Matrix.getRotateInstance(Math.toRadians(rotation), 0, 0));
+        contentStream.transform(Matrix.getTranslateInstance(-pivotX, -pivotY));
+
         contentStream.beginText();
         for (int i = 0; i < lines.length; i++) {
             String line = lines[i];
-            // Set the text matrix for each line with rotation
+            // Start from top line: yTop = adjustedY + blockHeight - capHeight
-            contentStream.setTextMatrix(
+            float yLine = adjustedY + blockHeight - capHeight - (i * lineHeight);
-                    Matrix.getRotateInstance(Math.toRadians(rotation), x, y - (i * lineHeight)));
+            contentStream.setTextMatrix(Matrix.getTranslateInstance(adjustedX, yLine));
             contentStream.showText(line);
         }
         contentStream.endText();
+        contentStream.restoreGraphicsState();
     }
 
     private void addImageStamp(
@@ -310,9 +330,17 @@ public class StampController {
         }
 
         contentStream.saveGraphicsState();
-        contentStream.transform(Matrix.getTranslateInstance(x, y));
+        // Rotate and scale about the center of the image
+        float centerX = x + (desiredPhysicalWidth / 2f);
+        float centerY = y + (desiredPhysicalHeight / 2f);
+        contentStream.transform(Matrix.getTranslateInstance(centerX, centerY));
         contentStream.transform(Matrix.getRotateInstance(Math.toRadians(rotation), 0, 0));
-        contentStream.drawImage(xobject, 0, 0, desiredPhysicalWidth, desiredPhysicalHeight);
+        contentStream.drawImage(
+                xobject,
+                -desiredPhysicalWidth / 2f,
+                -desiredPhysicalHeight / 2f,
+                desiredPhysicalWidth,
+                desiredPhysicalHeight);
         contentStream.restoreGraphicsState();
     }
 

frontend/src/tools/AddStamp.tsx

@@ -11,7 +11,6 @@ import StampPreview from "../components/tools/addStamp/StampPreview";
 import LocalIcon from "../components/shared/LocalIcon";
 import styles from "../components/tools/addStamp/StampPreview.module.css";
 import { Tooltip } from "../components/shared/Tooltip";
-import FitText from "../components/shared/FitText";
 import ButtonSelector from "../components/shared/ButtonSelector";
 
 const AddStamp = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {