Increase watermark coverage to fill page with the new calculation (#2049

)

src/main/java/stirling/software/SPDF/controller/api/security/WatermarkController.java

@@ -187,24 +187,32 @@ private void addTextWatermark(
         float watermarkHeight = heightSpacer + fontSize * textLines.length;
         float pageWidth = page.getMediaBox().getWidth();
         float pageHeight = page.getMediaBox().getHeight();
-        int watermarkRows = (int) (pageHeight / watermarkHeight + 1);
-        int watermarkCols = (int) (pageWidth / watermarkWidth + 1);
 
-        // Calculating the effective line length according to the angle used
-        float effectiveHeight = watermarkHeight / (float) Math.cos(Math.toRadians(rotation));
-        int watermarkRowsRotation = (int) (pageHeight / effectiveHeight + 1);
+
+        //Calculating the new width and height depending on the angle.
+        float radians = (float) Math.toRadians(rotation);
+        float newWatermarkWidth =
+                (float)
+                        (Math.abs(watermarkWidth * Math.cos(radians))
+                                + Math.abs(watermarkHeight * Math.sin(radians)));
+        float newWatermarkHeight =
+                (float)
+                        (Math.abs(watermarkWidth * Math.sin(radians))
+                                + Math.abs(watermarkHeight * Math.cos(radians)));
+
+        //Calculating the number of rows and columns.
+        int watermarkRows = (int) (pageHeight / newWatermarkHeight + 1);
+        int watermarkCols = (int) (pageWidth / newWatermarkWidth + 1);
 
         // Add the text watermark
-        /* In the 'for' loop, is do (watermarkRowsRotation - watermarkRows) so that the watermark starts at the bottom of the page.
-        This compensate for the rotation by adjusting the starting point for inserting the watermark. */
-        for (int i = (watermarkRowsRotation - watermarkRows); i < watermarkRows; i++) {
-            for (int j = 0; j < watermarkCols; j++) {
+        for (int i = 0; i <= watermarkRows; i++) {
+            for (int j = 0; j <= watermarkCols; j++) {
                 contentStream.beginText();
                 contentStream.setTextMatrix(
                         Matrix.getRotateInstance(
                                 (float) Math.toRadians(rotation),
-                                j * watermarkWidth,
-                                i * watermarkHeight));
+                                j * newWatermarkWidth,
+                                i * newWatermarkHeight));
 
                 for (int k = 0; k < textLines.length; ++k) {
                     contentStream.showText(textLines[k]);