Constraint size and alignment simultaneously

Previously, the size was scaled to fit the requested maximum size and
then aligned. If the maximum size was not a multiple of the alignment,
the resulting size was suboptimal as it preserved the aspect ratio less
accurately.

This also prepares for additional video constraints.

PR #6766 <https://github.com/Genymobile/scrcpy/pull/6766>

server/src/main/java/com/genymobile/scrcpy/device/Size.java

@@ -29,59 +29,35 @@ public final class Size {
         return new Size(height, width);
     }
 
-    public Size limit(int maxSize) {
+    public Size constrain(int maxSize, int alignment) {
         assert maxSize >= 0 : "Max size may not be negative";
+        assert alignment > 0 : "Alignment must be positive";
+        assert (alignment & (alignment - 1)) == 0 : "Alignment must be a power-of-two";
 
-        if (maxSize == 0) {
-            // No limit
-            return this;
+        int alignedMaxSize = maxSize / alignment * alignment; // round to a multiple of alignment
+        int w, h;
+
+        if (maxSize > 0 && (width > alignedMaxSize || height > alignedMaxSize)) {
+            if (width > height) {
+                w = alignedMaxSize;
+                h = round(height * alignedMaxSize / width, alignment);
+            } else {
+                w = round(width * alignedMaxSize / height, alignment);
+                h = alignedMaxSize;
+            }
+        } else {
+            w = round(width, alignment);
+            h = round(height, alignment);
         }
 
-        boolean portrait = height > width;
-        int major = portrait ? height : width;
-        if (major <= maxSize) {
-            return this;
-        }
+        assert maxSize == 0 || w <= maxSize : "The width cannot exceed maxSize if maxSize is aligned";
+        assert maxSize == 0 || h <= maxSize : "The height cannot exceed maxSize if maxSize is aligned";
 
-        int minor = portrait ? width : height;
-
-        int newMajor = maxSize;
-        int newMinor = maxSize * minor / major;
-
-        int w = portrait ? newMinor : newMajor;
-        int h = portrait ? newMajor : newMinor;
         return new Size(w, h);
     }
 
-    /**
-     * Round both dimensions of this size to be multiples of {@code alignment}.
-     *
-     * @param alignment the required alignment
-     * @return the current size rounded
-     */
-    public Size round(int alignment) {
-        if (isMultipleOf(alignment)) {
-            // Already aligned
-            return this;
-        }
-
-        boolean portrait = height > width;
-        int major = portrait ? height : width;
-        int minor = portrait ? width : height;
-
-        major = major / alignment * alignment; // round down to not exceed the initial size
-        minor = (minor + (alignment / 2)) / alignment * alignment; // round to the nearest to minimize aspect ratio distortion
-        if (minor > major) {
-            minor = major;
-        }
-
-        int w = portrait ? minor : major;
-        int h = portrait ? major : minor;
-        return new Size(w, h);
-    }
-
-    public boolean isMultipleOf(int alignment) {
-        return width % alignment == 0 && height % alignment == 0;
+    private static int round(int value, int alignment) {
+        return (value + (alignment / 2)) / alignment * alignment;
     }
 
     public Rect toRect() {

server/src/main/java/com/genymobile/scrcpy/video/CameraCapture.java

@@ -149,7 +149,7 @@ public class CameraCapture extends SurfaceCapture {
         filter.addAngle(angle);
 
         transform = filter.getInverseTransform();
-        videoSize = filter.getOutputSize().limit(maxSize).round(getAlignment());
+        videoSize = filter.getOutputSize().constrain(maxSize, getAlignment());
     }
 
     private static String selectCamera(String explicitCameraId, CameraFacing cameraFacing) throws CameraAccessException, ConfigurationException {

server/src/main/java/com/genymobile/scrcpy/video/NewDisplayCapture.java

@@ -133,13 +133,9 @@ public class NewDisplayCapture extends SurfaceCapture {
         filter.addOrientation(displayRotation, captureOrientationLocked, captureOrientation);
         filter.addAngle(angle);
 
-        int alignment = getAlignment();
-        Size filteredSize = filter.getOutputSize();
-        if (!filteredSize.isMultipleOf(alignment) || (maxSize != 0 && filteredSize.getMax() > maxSize)) {
-            if (maxSize != 0) {
-                filteredSize = filteredSize.limit(maxSize);
-            }
-            filteredSize = filteredSize.round(alignment);
+        Size outputSize = filter.getOutputSize();
+        Size filteredSize = outputSize.constrain(maxSize, getAlignment());
+        if (!filteredSize.equals(outputSize)) {
             filter.addResize(filteredSize);
         }
 

server/src/main/java/com/genymobile/scrcpy/video/ScreenCapture.java

@@ -97,7 +97,7 @@ public class ScreenCapture extends SurfaceCapture {
         filter.addAngle(angle);
 
         transform = filter.getInverseTransform();
-        videoSize = filter.getOutputSize().limit(maxSize).round(getAlignment());
+        videoSize = filter.getOutputSize().constrain(maxSize, getAlignment());
     }
 
     @Override

server/src/test/java/com/genymobile/scrcpy/device/SizeTest.java

@@ -0,0 +1,35 @@
+package com.genymobile.scrcpy.device;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SizeTest {
+    @Test
+    public void testConstrainSize() {
+        Size size = new Size(207, 209);
+
+        Assert.assertEquals(size, size.constrain(0, 1));
+        Assert.assertEquals(new Size(208, 210), size.constrain(0, 2));
+        Assert.assertEquals(new Size(208, 208), size.constrain(0, 4));
+
+        Size s = size.constrain(208, 2);
+        Assert.assertEquals(208, s.getHeight());
+        Assert.assertTrue(s.getWidth() >= 206 && s.getWidth() <= 208 && s.getWidth() % 2 == 0);
+
+        Assert.assertEquals(new Size(207 * 208 / 209, 208), size.constrain(208, 2));
+        Assert.assertEquals(new Size(208, 208), size.constrain(208, 4));
+    }
+
+    @Test
+    public void testConstrainSizeUnchanged() {
+        Size size = new Size(256, 512);
+
+        Assert.assertEquals(size, size.constrain(0, 1));
+        Assert.assertEquals(size, size.constrain(512, 1));
+        Assert.assertEquals(size, size.constrain(515, 1));
+        Assert.assertEquals(size, size.constrain(512, 16));
+        Assert.assertEquals(size, size.constrain(515, 16));
+        Assert.assertEquals(size, size.constrain(0, 16));
+        Assert.assertEquals(size, size.constrain(4096, 16));
+    }
+}