From e8be1f960099d16b4db81c09e483d6e936b2d833 Mon Sep 17 00:00:00 2001
From: Marek Ossowski <marek0ossowski@gmail.com>
Date: Sat, 2 Aug 2025 21:36:37 +0200
Subject: [PATCH] First version of HF Fax mode (copied from raw mode)

---
 app/src/main/java/xdsopl/robot36/Decoder.java |  4 +
 app/src/main/java/xdsopl/robot36/HFFax.java   | 86 +++++++++++++++++++
 .../java/xdsopl/robot36/MainActivity.java     |  4 +
 app/src/main/res/menu/menu_main.xml           |  5 ++
 app/src/main/res/values/strings.xml           |  1 +
 5 files changed, 100 insertions(+)
 create mode 100644 app/src/main/java/xdsopl/robot36/HFFax.java

diff --git a/app/src/main/java/xdsopl/robot36/Decoder.java b/app/src/main/java/xdsopl/robot36/Decoder.java
index dc7d9ea..caeccd6 100644
--- a/app/src/main/java/xdsopl/robot36/Decoder.java
+++ b/app/src/main/java/xdsopl/robot36/Decoder.java
@@ -38,6 +38,7 @@ public class Decoder {
 	private final int visCodeBitSamples;
 	private final int visCodeSamples;
 	private final Mode rawMode;
+	private final Mode hffaxMode;
 	private final ArrayList<Mode> syncPulse5msModes;
 	private final ArrayList<Mode> syncPulse9msModes;
 	private final ArrayList<Mode> syncPulse20msModes;
@@ -95,6 +96,7 @@ public class Decoder {
 		double scanLineToleranceSeconds = 0.001;
 		scanLineToleranceSamples = (int) Math.round(scanLineToleranceSeconds * sampleRate);
 		rawMode = new RawDecoder(rawName, sampleRate);
+		hffaxMode = new HFFax("HF Fax", sampleRate);
 		Mode robot36 = new Robot_36_Color(sampleRate);
 		currentMode = robot36;
 		currentScanLineSamples = robot36.getScanLineSamples();
@@ -450,6 +452,8 @@ public class Decoder {
 			mode = findMode(syncPulse9msModes, name);
 		if (mode == null)
 			mode = findMode(syncPulse20msModes, name);
+		if (mode == null && hffaxMode.getName().equals(name))
+			mode = hffaxMode;
 		if (mode == currentMode) {
 			lockMode = true;
 			return;
diff --git a/app/src/main/java/xdsopl/robot36/HFFax.java b/app/src/main/java/xdsopl/robot36/HFFax.java
new file mode 100644
index 0000000..5854419
--- /dev/null
+++ b/app/src/main/java/xdsopl/robot36/HFFax.java
@@ -0,0 +1,86 @@
+package xdsopl.robot36;
+
+public class HFFax implements Mode {
+    private final ExponentialMovingAverage lowPassFilter;
+    private final int smallPictureMaxSamples;
+    private final int mediumPictureMaxSamples;
+    private final String name;
+
+    private final int sr;
+
+    HFFax(String name, int sampleRate) {
+        this.name = name;
+        smallPictureMaxSamples = (int) Math.round(0.125 * sampleRate);
+        mediumPictureMaxSamples = (int) Math.round(0.175 * sampleRate);
+        lowPassFilter = new ExponentialMovingAverage();
+        this.sr = sampleRate;
+    }
+
+    private float freqToLevel(float frequency, float offset) {
+        return 0.5f * (frequency - offset + 1.f);
+    }
+
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public int getCode() {
+        return -1;
+    }
+
+    @Override
+    public int getWidth() {
+        return -1;
+    }
+
+    @Override
+    public int getHeight() {
+        return -1;
+    }
+
+    @Override
+    public int getBegin() {
+        return 0;
+    }
+
+    @Override
+    public int getFirstSyncPulseIndex() {
+        return -1;
+    }
+
+    @Override
+    public int getScanLineSamples() {
+        return sr / 2;
+    }
+
+    @Override
+    public void reset() {
+    }
+
+    @Override
+    public boolean decodeScanLine(PixelBuffer pixelBuffer, float[] scratchBuffer, float[] scanLineBuffer, int scopeBufferWidth, int syncPulseIndex, int scanLineSamples, float frequencyOffset) {
+        if (syncPulseIndex < 0 || syncPulseIndex + scanLineSamples > scanLineBuffer.length)
+            return false;
+        int horizontalPixels = scopeBufferWidth;
+        if (scanLineSamples < smallPictureMaxSamples)
+            horizontalPixels /= 2;
+        if (scanLineSamples < mediumPictureMaxSamples)
+            horizontalPixels /= 2;
+        lowPassFilter.cutoff(horizontalPixels, 2 * scanLineSamples, 2);
+        lowPassFilter.reset();
+        for (int i = 0; i < scanLineSamples; ++i)
+            scratchBuffer[i] = lowPassFilter.avg(scanLineBuffer[syncPulseIndex + i]);
+        lowPassFilter.reset();
+        for (int i = scanLineSamples - 1; i >= 0; --i)
+            scratchBuffer[i] = freqToLevel(lowPassFilter.avg(scratchBuffer[i]), frequencyOffset);
+        for (int i = 0; i < horizontalPixels; ++i) {
+            int position = (i * scanLineSamples) / horizontalPixels;
+            pixelBuffer.pixels[i] = ColorConverter.GRAY(scratchBuffer[position]);
+        }
+        pixelBuffer.width = horizontalPixels;
+        pixelBuffer.height = 1;
+        return true;
+    }
+}
diff --git a/app/src/main/java/xdsopl/robot36/MainActivity.java b/app/src/main/java/xdsopl/robot36/MainActivity.java
index 0a51384..2ed2563 100644
--- a/app/src/main/java/xdsopl/robot36/MainActivity.java
+++ b/app/src/main/java/xdsopl/robot36/MainActivity.java
@@ -612,6 +612,10 @@ public class MainActivity extends AppCompatActivity {
 			setMode(R.string.raw_mode);
 			return true;
 		}
+		if (id == R.id.action_force_hffax_mode) {
+			setMode("HF Fax");
+			return true;
+		}
 		if (id == R.id.action_force_robot36_color) {
 			setMode(R.string.robot36_color);
 			return true;
diff --git a/app/src/main/res/menu/menu_main.xml b/app/src/main/res/menu/menu_main.xml
index c06b4d5..25e28e5 100644
--- a/app/src/main/res/menu/menu_main.xml
+++ b/app/src/main/res/menu/menu_main.xml
@@ -102,6 +102,11 @@
 						android:icon="@drawable/baseline_image_not_supported_24"
 						android:title="@string/raw_mode"
 						app:iconTint="@color/tint" />
+					<item
+						android:id="@+id/action_force_hffax_mode"
+						android:icon="@drawable/baseline_image_not_supported_24"
+						android:title="@string/hffax_mode"
+						app:iconTint="@color/tint" />
 					<item
 						android:id="@+id/action_auto_mode"
 						android:icon="@drawable/baseline_auto_mode_24"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 210acc3..7a765dc 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -44,6 +44,7 @@
 	<string name="auto_mode">Auto Mode</string>
 	<string name="lock_mode">Lock Mode</string>
 	<string name="raw_mode">Raw Mode</string>
+	<string name="hffax_mode">HF Fax Mode</string>
 	<string name="listening">Listening</string>
 	<string name="audio_settings">Audio Settings</string>
 	<string name="sample_rate">Sample Rate</string>