Add Chart.setSize so a chart can be resized before export

README.md

@@ -167,6 +167,13 @@ ChartEncoder.saveChart(chart, outputStream, "png");
 byte[] bytes = ChartEncoder.getBytes(chart, "png");
 ```
 
+To export a chart at a different size than it was built with, for example a chart constructed by code you don't control, resize it first with `setSize`:
+
+```java
+chart.setSize(1920, 1080);
+ChartEncoder.saveChart(chart, "./MyChart", "png");
+```
+
 * **Raster formats** (`png`, `jpg`, `bmp`, `gif`, `tiff`) are delegated to `javax.imageio.ImageIO`. Any other format for which an `ImageWriter` plugin is registered on the classpath works too — e.g. add `com.github.usefulness:webp-imageio` to export `webp` (see the `ExampleWebP` demo), or an AVIF plugin to export `avif`. Call `ChartEncoder.getSupportedRasterFormats()` to see what the current classpath can write. For AVIF, where no bundleable ImageIO writer exists yet, the `ExampleAvif` demo shows a portable fallback that pipes a PNG through the `avifenc` CLI (`brew install libavif`).
 * **Vector formats** (`svg`, `eps`, `pdf`) require the optional dependencies below.
 

xchart-demo/src/main/java/org/knowm/xchart/standalone/issues/TestForIssue807.java

@@ -0,0 +1,36 @@
+package org.knowm.xchart.standalone.issues;
+
+import java.io.IOException;
+import org.knowm.xchart.ChartEncoder;
+import org.knowm.xchart.SwingWrapper;
+import org.knowm.xchart.XYChart;
+import org.knowm.xchart.XYChartBuilder;
+
+/**
+ * Demonstrates resizing an already constructed chart before export, so a chart received from
+ * elsewhere can be saved at any dimensions. https://github.com/knowm/XChart/issues/807
+ */
+public class TestForIssue807 {
+
+  public static void main(String[] args) throws IOException {
+
+    XYChart chart = getChart();
+    chart.setSize(1280, 720);
+    ChartEncoder.saveChart(chart, "./TestForIssue807", "png");
+    new SwingWrapper<>(chart).displayChart();
+  }
+
+  public static XYChart getChart() {
+
+    XYChart chart =
+        new XYChartBuilder()
+            .width(640)
+            .height(480)
+            .title("Resized before export")
+            .xAxisTitle("Time")
+            .yAxisTitle("Value")
+            .build();
+    chart.addSeries("Sample", new double[] {0, 1, 2, 3, 4}, new double[] {1, 3, 2, 5, 4});
+    return chart;
+  }
+}

xchart/src/main/java/org/knowm/xchart/internal/chartpart/Chart.java

@@ -96,6 +96,26 @@ protected void setHeight(int height) {
     this.height = height;
   }
 
+  /**
+   * Sets the chart's width and height in pixels. This is useful for a chart constructed elsewhere
+   * that should be exported or displayed at a different size than it was built with. Exporters
+   * such as {@code ChartEncoder} lay the chart out at these dimensions.
+   *
+   * @param width the new width, greater than 0
+   * @param height the new height, greater than 0
+   * @return this chart, for chaining
+   * @throws IllegalArgumentException if either dimension is not positive
+   */
+  public Chart<ST, S> setSize(int width, int height) {
+
+    if (width <= 0 || height <= 0) {
+      throw new IllegalArgumentException("Chart width and height must be greater than 0 !!!");
+    }
+    this.width = width;
+    this.height = height;
+    return this;
+  }
+
   // TODO remove public
   public String getTitle() {
 

xchart/src/test/java/org/knowm/xchart/ChartSizeTest.java

@@ -0,0 +1,94 @@
+package org.knowm.xchart;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.awt.image.BufferedImage;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import javax.imageio.ImageIO;
+import org.apache.pdfbox.Loader;
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.junit.jupiter.api.Test;
+
+/** https://github.com/knowm/XChart/issues/807 */
+public class ChartSizeTest {
+
+  private static XYChart sampleChart() {
+    XYChart chart = new XYChartBuilder().width(500).height(400).title("Sample").build();
+    chart.addSeries("y(x)", new double[] {0, 1, 2}, new double[] {2, 1, 0});
+    return chart;
+  }
+
+  @Test
+  public void setSizeUpdatesDimensionsAndChains() {
+
+    XYChart chart = sampleChart();
+    assertThat(chart.setSize(1920, 1080)).isSameAs(chart);
+    assertThat(chart.getWidth()).isEqualTo(1920);
+    assertThat(chart.getHeight()).isEqualTo(1080);
+  }
+
+  @Test
+  public void setSizeRejectsNonPositiveDimensions() {
+
+    XYChart chart = sampleChart();
+    for (int[] size : new int[][] {{0, 100}, {100, 0}, {-1, 100}, {100, -1}}) {
+      assertThatThrownBy(() -> chart.setSize(size[0], size[1]))
+          .isInstanceOf(IllegalArgumentException.class);
+    }
+    assertThat(chart.getWidth()).isEqualTo(500);
+    assertThat(chart.getHeight()).isEqualTo(400);
+  }
+
+  @Test
+  public void rasterExportUsesNewSize() throws IOException {
+
+    XYChart chart = sampleChart();
+    chart.setSize(800, 300);
+    BufferedImage image =
+        ImageIO.read(new ByteArrayInputStream(ChartEncoder.getBytes(chart, "png")));
+    assertThat(image.getWidth()).isEqualTo(800);
+    assertThat(image.getHeight()).isEqualTo(300);
+  }
+
+  @Test
+  public void vectorExportUsesNewSize() throws IOException {
+
+    XYChart chart = sampleChart();
+    chart.setSize(720, 360);
+
+    String svg = new String(ChartEncoder.getBytes(chart, "svg"), StandardCharsets.UTF_8);
+    Matcher viewBox = Pattern.compile("viewBox=\"([^\"]+)\"").matcher(svg);
+    assertThat(viewBox.find()).isTrue();
+    String[] bounds = viewBox.group(1).trim().split("\\s+");
+    assertThat(Double.parseDouble(bounds[2])).isEqualTo(720.0);
+    assertThat(Double.parseDouble(bounds[3])).isEqualTo(360.0);
+
+    try (PDDocument pdf = Loader.loadPDF(ChartEncoder.getBytes(chart, "pdf"))) {
+      assertThat(pdf.getPage(0).getMediaBox().getWidth()).isEqualTo(720.0f);
+      assertThat(pdf.getPage(0).getMediaBox().getHeight()).isEqualTo(360.0f);
+    }
+  }
+
+  @Test
+  public void setSizeWorksForOtherChartTypes() throws IOException {
+
+    PieChart pie = new PieChartBuilder().width(500).height(400).build();
+    pie.addSeries("A", 3);
+    pie.setSize(300, 600);
+    BufferedImage image = ImageIO.read(new ByteArrayInputStream(ChartEncoder.getBytes(pie, "png")));
+    assertThat(image.getWidth()).isEqualTo(300);
+    assertThat(image.getHeight()).isEqualTo(600);
+
+    CategoryChart bars = new CategoryChartBuilder().width(500).height(400).build();
+    bars.addSeries("Sample", new double[] {1, 2, 3}, new double[] {2, 4, 3});
+    bars.setSize(640, 200);
+    image = ImageIO.read(new ByteArrayInputStream(ChartEncoder.getBytes(bars, "png")));
+    assertThat(image.getWidth()).isEqualTo(640);
+    assertThat(image.getHeight()).isEqualTo(200);
+  }
+}