Add show methods

richtextfx-demos/src/main/java/org/fxmisc/richtext/demo/ShowLineDemo.java

@@ -0,0 +1,100 @@
+package org.fxmisc.richtext.demo;
+
+import javafx.application.Application;
+import javafx.event.ActionEvent;
+import javafx.geometry.Pos;
+import javafx.scene.Scene;
+import javafx.scene.control.Button;
+import javafx.scene.control.TextField;
+import javafx.scene.layout.BorderPane;
+import javafx.scene.layout.VBox;
+import javafx.stage.Stage;
+import org.fxmisc.flowless.VirtualizedScrollPane;
+import org.fxmisc.richtext.InlineCssTextArea;
+
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+public class ShowLineDemo extends Application {
+
+    public static final int MIN_LINE_INDEX = 0;
+
+    private class NumbersOnlyField extends TextField {
+
+        NumbersOnlyField() {
+            super();
+            setOnKeyTyped(ke -> {
+                String keyEventText = ke.getCharacter();
+                if (Character.isDigit(keyEventText.charAt(0))) {
+                    if (getSelectedText().isEmpty()) {
+                        appendText(keyEventText);
+                    } else {
+                        replaceText(getSelection(), keyEventText);
+                    }
+                }
+                ke.consume();
+            });
+        }
+
+        public int getTextAsInt() {
+            String text = getText();
+            if (text.isEmpty()) {
+                setText(String.valueOf(MIN_LINE_INDEX));
+                return MIN_LINE_INDEX;
+            } else {
+                return Integer.parseInt(text);
+            }
+        }
+
+    }
+
+    private final NumbersOnlyField field = new NumbersOnlyField();
+    {
+        field.setPromptText("Input a number to indicate which line you want to show");
+    }
+
+    @Override
+    public void start(Stage primaryStage) throws Exception {
+        StringBuilder sb = new StringBuilder();
+        int max = 100;
+        for (int i = 0; i < max; i++) {
+            sb.append("Line Index: ").append(i).append("\n");
+        }
+        sb.append("Line Index: ").append(max);
+        InlineCssTextArea area = new InlineCssTextArea(sb.toString());
+        VirtualizedScrollPane<InlineCssTextArea> vsPane = new VirtualizedScrollPane<>(area);
+
+        Function<Integer, Integer> clamp = i -> Math.max(0, Math.min(i, area.getLength() - 1));
+        Button showInViewportButton = createButton("Show line somewhere in Viewport", ae -> {
+            area.showParagraphInViewport(clamp.apply(field.getTextAsInt()));
+        });
+        Button showAtViewportTopButton = createButton("Show line at top of viewport", ae -> {
+            area.showParagraphAtTop(clamp.apply(field.getTextAsInt()));
+        });
+        Button showAtViewportBottomButton = createButton("Show line at bottom of viewport", ae -> {
+            area.showParagraphAtBottom(clamp.apply(field.getTextAsInt()));
+        });
+
+        VBox vbox = new VBox(field, showInViewportButton, showAtViewportTopButton, showAtViewportBottomButton);
+        vbox.setAlignment(Pos.CENTER);
+
+        BorderPane root = new BorderPane();
+        root.setCenter(vsPane);
+        root.setBottom(vbox);
+
+        Scene scene = new Scene(root, 700, 500);
+        primaryStage.setScene(scene);
+        primaryStage.show();
+
+    }
+
+    private Button createButton(String text, Consumer<ActionEvent> handler) {
+        Button b = new Button(text);
+        b.setOnAction(ae -> {
+            handler.accept(ae);
+            field.requestFocus();
+        });
+        return b;
+    }
+
+}

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

@@ -962,6 +962,38 @@ void show(double y) {
         virtualFlow.show(y);
     }
 
+    /**
+     * Shows the paragraph somewhere in the viewport. If the line is already visible, no noticeable change occurs.
+     * If line is above the current view, it appears at the top of the viewport. If the line is below the current
+     * view, it appears at the bottom of the viewport.
+     */
+    public void showParagraphInViewport(int paragraphIndex) {
+        virtualFlow.show(paragraphIndex);
+    }
+
+    /**
+     * Lays out the viewport so that the paragraph is the first line (top) displayed in the viewport. Note: if
+     * the given area does not have enough lines that follow the given line to span its entire height, the paragraph
+     * may not appear at the very top of the viewport. Instead, it may simply be shown in the viewport. For example,
+     * given an unwrapped area whose height could show 10 lines but whose content only has 3 lines, calling
+     * {@code showParagraphAtTop(3)} would be no different than {@code showParagraphAtTop(1)}.
+     */
+    public void showParagraphAtTop(int paragraphIndex) {
+        virtualFlow.showAsFirst(paragraphIndex);
+    }
+
+    /**
+     * Lays out the viewport so that the paragraph is the last line (bottom) displayed in the viewport. Note: if
+     * the given area does not have enough lines preceding the given line to span its entire height, the paragraph
+     * may not appear at the very bottom of the viewport. Instead, it may appear towards the bottom of the viewport
+     * with some extra space following it. For example, given an unwrapped area whose height could show 10 lines but
+     * whose content only has 7 lines, calling {@code showParagraphAtBottom(1)} would be no different than calling
+     * {@code showParagraphAtBottom(7)}.
+     */
+    public void showParagraphAtBottom(int paragraphIndex) {
+        virtualFlow.showAsLast(paragraphIndex);
+    }
+
     void showCaretAtBottom() {
         int parIdx = getCurrentParagraph();
         Cell<Paragraph<PS, SEG, S>, ParagraphBox<PS, SEG, S>> cell = virtualFlow.getCell(parIdx);