Fix high DPI issue in ChartPanel - bug #170

jfree · Oct 23, 2020 · fa5a113 · fa5a113
1 parent 7dc25a0
commit fa5a113
Show file tree

Hide file tree

Showing 2 changed files with 38 additions and 15 deletions.
diff --git a/README.md b/README.md
@@ -26,6 +26,17 @@ The library is licensed under the terms of the GNU Lesser General Public
 License (LGPL) version 2.1 or later.
 
 
+Using JFreeChart
+----------------
+To use JFreeChart in your projects, add the following dependency to your build tool:
+
+    <dependency>
+        <groupId>org.jfree</groupId>
+        <artifactId>jfreechart</artifactId>
+        <version>1.5.1</version>
+    </dependency>
+
+
 Building JFreeChart
 -------------------
 You can build JFreeChart using Maven.  The build requires JDK 8 or later.
@@ -49,6 +60,7 @@ History
 -------
 
 ##### Version 1.5.1 (not yet released)
+- modify buffer in ChartPanel to handle high DPI displays (bug #170);
 - added Catalan translations (PR #117);
 - fix for LayeredBarRenderer (bug #169);
 - migrated to JUnit 5.

diff --git a/src/main/java/org/jfree/chart/ChartPanel.java b/src/main/java/org/jfree/chart/ChartPanel.java
@@ -2,7 +2,7 @@
  * JFreeChart : a free chart library for the Java(tm) platform
  * ===========================================================
  *
- * (C) Copyright 2000-2017, by Object Refinery Limited and Contributors.
+ * (C) Copyright 2000-2020, by Object Refinery Limited and Contributors.
  *
  * Project Info:  http://www.jfree.org/jfreechart/index.html
  *
@@ -218,8 +218,8 @@
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.util.ArrayList;
 import java.util.EventListener;
-import java.util.Iterator;
 import java.util.List;
 import java.util.ResourceBundle;
 
@@ -747,7 +747,7 @@ public ChartPanel(JFreeChart chart, int width, int height,
             this.panMask = InputEvent.ALT_MASK;
         }
 
-        this.overlays = new java.util.ArrayList<Overlay>();
+        this.overlays = new ArrayList<Overlay>();
     }
 
     /**
@@ -1566,12 +1566,21 @@ else if (drawHeight > this.maximumDrawHeight) {
         // are we using the chart buffer?
         if (this.useBuffer) {
 
+            // for better rendering on the HiDPI monitors upscaling the buffer to the "native" resoution
+            // instead of using logical one provided by Swing
+            final AffineTransform globalTransform = ((Graphics2D) g).getTransform();
+            final double globalScaleX = globalTransform.getScaleX();
+            final double globalScaleY = globalTransform.getScaleY();
+
+            final int scaledWidth = (int) (available.getWidth() * globalScaleX);
+            final int scaledHeight = (int) (available.getHeight() * globalScaleY);
+
             // do we need to resize the buffer?
             if ((this.chartBuffer == null)
-                    || (this.chartBufferWidth != available.getWidth())
-                    || (this.chartBufferHeight != available.getHeight())) {
-                this.chartBufferWidth = (int) available.getWidth();
-                this.chartBufferHeight = (int) available.getHeight();
+                    || (this.chartBufferWidth != scaledWidth)
+                    || (this.chartBufferHeight != scaledHeight)) {
+                this.chartBufferWidth = scaledWidth;
+                this.chartBufferHeight = scaledHeight;
                 GraphicsConfiguration gc = g2.getDeviceConfiguration();
                 this.chartBuffer = gc.createCompatibleImage(
                         this.chartBufferWidth, this.chartBufferHeight,
@@ -1584,17 +1593,19 @@ else if (drawHeight > this.maximumDrawHeight) {
 
                 this.refreshBuffer = false; // clear the flag
 
+                // scale graphics of the buffer to the same value as global 
+                // Swing graphics - this allow to paint all elements as usual 
+                // but applies all necessary smoothing
+                Graphics2D bufferG2 = (Graphics2D) this.chartBuffer.getGraphics();
+                bufferG2.scale(globalScaleX, globalScaleY);
+
                 Rectangle2D bufferArea = new Rectangle2D.Double(
-                        0, 0, this.chartBufferWidth, this.chartBufferHeight);
+                        0, 0, available.getWidth(), available.getHeight());
 
                 // make the background of the buffer clear and transparent
-                Graphics2D bufferG2 = (Graphics2D)
-                        this.chartBuffer.getGraphics();
                 Composite savedComposite = bufferG2.getComposite();
-                bufferG2.setComposite(AlphaComposite.getInstance(
-                        AlphaComposite.CLEAR, 0.0f));
-                Rectangle r = new Rectangle(0, 0, this.chartBufferWidth,
-                        this.chartBufferHeight);
+                bufferG2.setComposite(AlphaComposite.getInstance(AlphaComposite.CLEAR, 0.0f));
+                Rectangle r = new Rectangle(0, 0, (int) available.getWidth(), (int) available.getHeight());
                 bufferG2.fill(r);
                 bufferG2.setComposite(savedComposite);
 
@@ -1614,7 +1625,7 @@ else if (drawHeight > this.maximumDrawHeight) {
             }
 
             // zap the buffer onto the panel...
-            g2.drawImage(this.chartBuffer, insets.left, insets.top, this);
+            g2.drawImage(this.chartBuffer, insets.left, insets.top, (int) available.getWidth(), (int) available.getHeight(), this);
 
         } else { // redrawing the chart every time...
             AffineTransform saved = g2.getTransform();