Styled area refactor: Get bounds of paragraph on screen

richtextfx/src/main/java/org/fxmisc/richtext/GenericStyledArea.java

@@ -2091,23 +2091,7 @@ private Bounds getParagraphBoundsOnScreen(Cell<Paragraph<PS, SEG, S>, ParagraphB
         Bounds nodeScreen = cell.getNode().localToScreen(nodeLocal);
         Bounds areaLocal = getBoundsInLocal();
         Bounds areaScreen = localToScreen(areaLocal);
-
-        // use area's minX if scrolled right and paragraph's left is not visible
-        double minX = nodeScreen.getMinX() < areaScreen.getMinX()
-                ? areaScreen.getMinX()
-                : nodeScreen.getMinX();
-        // use area's minY if scrolled down vertically and paragraph's top is not visible
-        double minY = nodeScreen.getMinY() < areaScreen.getMinY()
-                ? areaScreen.getMinY()
-                : nodeScreen.getMinY();
-        // use area's width whether paragraph spans outside of it or not
-        // so that short or long paragraph takes up the entire space
-        double width = areaScreen.getWidth();
-        // use area's maxY if scrolled up vertically and paragraph's bottom is not visible
-        double maxY = nodeScreen.getMaxY() < areaScreen.getMaxY()
-                ? nodeScreen.getMaxY()
-                : areaScreen.getMaxY();
-        return new BoundingBox(minX, minY, width, maxY - minY);
+        return new ScreenBounds(areaScreen).getParagraphBoundsFrom(nodeScreen);
     }
 
     private Optional<Bounds> getRangeBoundsOnScreen(int paragraphIndex, int from, int to) {

richtextfx/src/main/java/org/fxmisc/richtext/ScreenBounds.java

@@ -0,0 +1,29 @@
+package org.fxmisc.richtext;
+
+import javafx.geometry.BoundingBox;
+import javafx.geometry.Bounds;
+
+class ScreenBounds {
+    private final Bounds screen;
+
+    public ScreenBounds(Bounds screen) {
+        this.screen = screen;
+    }
+
+    /**
+     * Evaluate the paragraph node bounds in the area.
+     * @param paragraph the paragraph bound position on screen
+     * @return the bounds inside the area of the provided paragraph bounds.
+     */
+    public Bounds getParagraphBoundsFrom(Bounds paragraph) {
+        // use area's minX,minY if scrolled right/down and paragraph's left/top is not visible
+        double minX = Math.max(paragraph.getMinX(), screen.getMinX());
+        double minY = Math.max(paragraph.getMinY(), screen.getMinY());
+        // use area's width whether paragraph spans outside of it or not
+        // so that short or long paragraph takes up the entire space
+        double width = screen.getWidth();
+        // use area's maxY if scrolled up vertically and paragraph's bottom is not visible
+        double maxY = Math.min(paragraph.getMaxY(), screen.getMaxY());
+        return new BoundingBox(minX, minY, width, maxY - minY);
+    }
+}

richtextfx/src/test/java/org/fxmisc/richtext/BoundsEvaluatorTest.java

@@ -0,0 +1,45 @@
+package org.fxmisc.richtext;
+
+import javafx.geometry.BoundingBox;
+import javafx.geometry.Bounds;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class BoundsEvaluatorTest {
+    private void checkBounds(Bounds bounds, double xMin, double yMin, double xMax, double yMax) {
+        assertEquals(xMin, bounds.getMinX(), "Invalid min X value");
+        assertEquals(yMin, bounds.getMinY(), "Invalid min Y value");
+        assertEquals(xMax, bounds.getMaxX(), "Invalid max X value");
+        assertEquals(yMax, bounds.getMaxY(), "Invalid max Y value");
+    }
+
+    @Test
+    @DisplayName("Evaluate paragraph bounds on screen")
+    void evaluateParagraphBoundsOnScreen() {
+        ScreenBounds boundsEvaluator = new ScreenBounds(new BoundingBox(20, 20, 100, 100));
+        // Start < Screen ; End < Screen
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(10, 10, 50, 50)),
+                20, 20, 120, 60);
+        // Start < Screen ; End > Screen
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(10, 10, 111, 111)),
+                20, 20, 120, 120);
+        // Start > Screen ; End > Screen
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(21, 21, 100, 100)),
+                21, 21, 121, 120);
+        // Start > Screen ; End < Screen
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(21, 21, 98, 98)),
+                21, 21, 121, 119);
+        // Start = Screen ; End = Screen
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(20, 20, 100, 100)),
+                20, 20, 120, 120);
+        // Miscellaneous
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(0, 0, 80, 80)),
+                20, 20, 120, 80);
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(30, 30, 120, 120)),
+                30, 30, 130, 120);
+        checkBounds(boundsEvaluator.getParagraphBoundsFrom(new BoundingBox(110, 110, 130, 130)),
+                110, 110, 210, 120);
+    }
+}