1 files changed, 58 insertions, 10 deletions

diff --git a/test-rig/Pixhash.java b/test-rig/Pixhash.java
index b35a560..3bd8c8a 100644
--- a/test-rig/Pixhash.java
+++ b/test-rig/Pixhash.java
@@ -1,9 +1,9 @@
-// Verify that a screencap PNG is non-uniform - i.e., MediaCodec
-// actually painted something. Exits 0 if the image has at least
-// `--min` percent of pixels that differ from pixel (0,0); 1 otherwise.
+// Verify a screencap. The default checks non-uniformity. --pattern also
+// requires the four large color fields drawn by the debug Pattern activity,
+// so ordinary app chrome cannot make a black video surface pass.
 //
 //   java test-rig/Pixhash.java <png>            # default min=5%
-//   java test-rig/Pixhash.java <png> --min 1
+//   java test-rig/Pixhash.java <png> --pattern
 //
 // ImageIO/BufferedImage live in java.desktop, which the image's
 // openjdk-17-jdk-headless package does ship (headless only disables
@@ -17,16 +17,26 @@ import java.awt.image.BufferedImage;
 public final class Pixhash {
 
     public static void main(String[] args) throws IOException {
-        if (args.length < 1) {
-            System.err.println("usage: java Pixhash.java <png> [--min N]");
-            System.exit(2);
-        }
+        if (args.length < 1) usage();
         double minPercent = 5.0;
+        boolean pattern = false;
         for (int i = 1; i < args.length; i++) {
-            if ("--min".equals(args[i]) && i + 1 < args.length) {
-                minPercent = Double.parseDouble(args[++i]);
+            if ("--min".equals(args[i])) {
+                if (++i >= args.length) usage();
+                try {
+                    minPercent = Double.parseDouble(args[i]);
+                } catch (NumberFormatException e) {
+                    usage();
+                }
+            } else if ("--pattern".equals(args[i])) {
+                pattern = true;
+            } else {
+                usage();
             }
         }
+        if (!Double.isFinite(minPercent) || minPercent < 0.0 || minPercent > 100.0) {
+            usage();
+        }
 
         BufferedImage img = ImageIO.read(new File(args[0]));
         if (img == null) {
@@ -50,5 +60,43 @@ public final class Pixhash {
             System.err.printf("pixhash: only %.2f%% differ, need %.2f%%%n", pct, minPercent);
             System.exit(1);
         }
+        if (pattern) checkPattern(img);
+    }
+
+    private static void usage() {
+        System.err.println("usage: java Pixhash.java <png> [--min N] [--pattern]");
+        System.exit(2);
+    }
+
+    private static void checkPattern(BufferedImage img) {
+        long red = 0, green = 0, blue = 0, yellow = 0, sampled = 0;
+        // Sampling every fourth pixel keeps the check cheap on 1080p images.
+        for (int y = 0; y < img.getHeight(); y += 4) {
+            for (int x = 0; x < img.getWidth(); x += 4) {
+                int rgb = img.getRGB(x, y);
+                int r = (rgb >>> 16) & 0xff;
+                int g = (rgb >>> 8) & 0xff;
+                int b = rgb & 0xff;
+                sampled++;
+                if (r >= 140 && g <= 110 && b <= 110) red++;
+                else if (g >= 110 && r <= 120 && b <= 120) green++;
+                else if (b >= 140 && r <= 110 && g <= 130) blue++;
+                else if (r >= 140 && g >= 120 && b <= 120) yellow++;
+            }
+        }
+        double rp = 100.0 * red / sampled;
+        double gp = 100.0 * green / sampled;
+        double bp = 100.0 * blue / sampled;
+        double yp = 100.0 * yellow / sampled;
+        System.out.printf("pixhash: pattern red=%.2f green=%.2f blue=%.2f yellow=%.2f%%%n",
+                rp, gp, bp, yp);
+        // A rotated 16:9 target fills only about one third of a portrait
+        // source after correct letterboxing. Require every field and strong
+        // combined coverage rather than assuming the video fills the screen.
+        if (rp < 5.0 || gp < 5.0 || bp < 5.0 || yp < 5.0
+                || rp + gp + bp + yp < 25.0) {
+            System.err.println("pixhash: expected four-color target pattern was not rendered");
+            System.exit(1);
+        }
     }
 }