feat: backport of PWA icon image lazy generation (#21263)

This commit is a backport of #16994 (limited to PWA icon handling)

Fixes #21253

Author: mcollovati

flow-server/src/main/java/com/vaadin/flow/server/PwaIcon.java

@@ -9,6 +9,9 @@
 package com.vaadin.flow.server;
 
 import javax.imageio.ImageIO;
+import java.awt.Color;
+import java.awt.Graphics2D;
+import java.awt.Image;
 import java.awt.image.BufferedImage;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -56,6 +59,8 @@ public enum Domain {
     private final Map<String, String> attributes = new HashMap<>();
     private String tag = "link";
 
+    private PwaRegistry registry;
+
     PwaIcon(int width, int height, String baseName) {
         this(width, height, baseName, Domain.HEADER);
     }
@@ -202,6 +207,10 @@ public Domain getDomain() {
         return domain;
     }
 
+    public void setRegistry(PwaRegistry registry) {
+        this.registry = registry;
+    }
+
     /**
      * Sets the image presenting the icon.
      *
@@ -227,6 +236,11 @@ public void setImage(BufferedImage image) {
      *            output stream to write the icon image to
      */
     public void write(OutputStream outputStream) {
+        if (data == null) {
+            // New image with wanted size
+            // Store byte array and hashcode of image (GeneratedImage)
+            setImage(drawIconImage(getBaseImage()));
+        }
         try {
             outputStream.write(data);
         } catch (IOException ioe) {
@@ -236,4 +250,49 @@ public void write(OutputStream outputStream) {
         }
     }
 
+    // visible for test
+    protected BufferedImage getBaseImage() {
+        return registry.getBaseImage();
+    }
+
+    private BufferedImage drawIconImage(BufferedImage baseImage) {
+        // Pick top-left pixel as fill color if needed for image
+        // resizing
+        int bgColor = baseImage.getRGB(0, 0);
+
+        BufferedImage bimage = new BufferedImage(this.getWidth(),
+                this.getHeight(), BufferedImage.TYPE_INT_ARGB);
+        // Draw the image on to the buffered image
+        Graphics2D graphics = bimage.createGraphics();
+
+        // fill bg with fill-color
+        graphics.setBackground(new Color(bgColor, true));
+        graphics.clearRect(0, 0, this.getWidth(), this.getHeight());
+
+        // calculate ratio (bigger ratio) for resize
+        float ratio = (float) baseImage.getWidth()
+                / (float) this.getWidth() > (float) baseImage.getHeight()
+                        / (float) this.getHeight()
+                                ? (float) baseImage.getWidth()
+                                        / (float) this.getWidth()
+                                : (float) baseImage.getHeight()
+                                        / (float) this.getHeight();
+
+        // Forbid upscaling of image
+        ratio = ratio > 1.0f ? ratio : 1.0f;
+
+        // calculate sizes with ratio
+        int newWidth = Math.round(baseImage.getHeight() / ratio);
+        int newHeight = Math.round(baseImage.getWidth() / ratio);
+
+        // draw rescaled img in the center of created image
+        graphics.drawImage(
+                baseImage.getScaledInstance(newWidth, newHeight,
+                        Image.SCALE_SMOOTH),
+                (this.getWidth() - newWidth) / 2,
+                (this.getHeight() - newHeight) / 2, null);
+        graphics.dispose();
+        return bimage;
+    }
+
 }

flow-server/src/main/java/com/vaadin/flow/server/PwaRegistry.java

@@ -11,9 +11,6 @@
 import javax.imageio.ImageIO;
 import javax.servlet.ServletContext;
 
-import java.awt.Color;
-import java.awt.Graphics2D;
-import java.awt.Image;
 import java.awt.image.BufferedImage;
 import java.io.BufferedReader;
 import java.io.IOException;
@@ -75,6 +72,7 @@ public class PwaRegistry implements Serializable {
     private long offlineHash;
     private List<PwaIcon> icons = new ArrayList<>();
     private final PwaConfiguration pwaConfiguration;
+    private BufferedImage baseImage;
 
     /**
      * Creates a new PwaRegistry instance.
@@ -109,6 +107,10 @@ public PwaRegistry(PWA pwa, ServletContext servletContext)
         initializeResources(servletContext);
     }
 
+    BufferedImage getBaseImage() {
+        return baseImage;
+    }
+
     private void initializeResources(ServletContext servletContext)
             throws MalformedURLException, IOException {
         if (!pwaConfiguration.isEnabled()) {
@@ -126,17 +128,13 @@ private void initializeResources(ServletContext servletContext)
 
         // Load base logo from servlet context if available
         // fall back to local image if unavailable
-        BufferedImage baseImage = getBaseImage(logo);
+        baseImage = getBaseImage(logo);
 
         if (baseImage == null) {
             getLogger().error("Image is not found or can't be loaded: " + logo);
         } else {
-            // Pick top-left pixel as fill color if needed for image
-            // resizing
-            int bgColor = baseImage.getRGB(0, 0);
-
             // initialize icons
-            icons = initializeIcons(baseImage, bgColor);
+            icons = initializeIcons();
         }
 
         // Load offline page as string, from servlet context if
@@ -171,54 +169,14 @@ private URL getResourceUrl(ServletContext context, String path)
         return resourceUrl;
     }
 
-    private List<PwaIcon> initializeIcons(BufferedImage baseImage,
-            int bgColor) {
+    private List<PwaIcon> initializeIcons() {
         for (PwaIcon icon : getIconTemplates(pwaConfiguration.getIconPath())) {
-            // New image with wanted size
-            icon.setImage(drawIconImage(baseImage, bgColor, icon));
-            // Store byte array and hashcode of image (GeneratedImage)
+            icon.setRegistry(this);
             icons.add(icon);
         }
         return icons;
     }
 
-    private BufferedImage drawIconImage(BufferedImage baseImage, int bgColor,
-            PwaIcon icon) {
-        BufferedImage bimage = new BufferedImage(icon.getWidth(),
-                icon.getHeight(), BufferedImage.TYPE_INT_ARGB);
-        // Draw the image on to the buffered image
-        Graphics2D graphics = bimage.createGraphics();
-
-        // fill bg with fill-color
-        graphics.setBackground(new Color(bgColor, true));
-        graphics.clearRect(0, 0, icon.getWidth(), icon.getHeight());
-
-        // calculate ratio (bigger ratio) for resize
-        float ratio = (float) baseImage.getWidth()
-                / (float) icon.getWidth() > (float) baseImage.getHeight()
-                        / (float) icon.getHeight()
-                                ? (float) baseImage.getWidth()
-                                        / (float) icon.getWidth()
-                                : (float) baseImage.getHeight()
-                                        / (float) icon.getHeight();
-
-        // Forbid upscaling of image
-        ratio = ratio > 1.0f ? ratio : 1.0f;
-
-        // calculate sizes with ratio
-        int newWidth = Math.round(baseImage.getHeight() / ratio);
-        int newHeight = Math.round(baseImage.getWidth() / ratio);
-
-        // draw rescaled img in the center of created image
-        graphics.drawImage(
-                baseImage.getScaledInstance(newWidth, newHeight,
-                        Image.SCALE_SMOOTH),
-                (icon.getWidth() - newWidth) / 2,
-                (icon.getHeight() - newHeight) / 2, null);
-        graphics.dispose();
-        return bimage;
-    }
-
     /**
      * Creates manifest.webmanifest json object.
      *