Dissociate virtual display size and capture size

Allow capturing virtual displays at a lower resolution using
-m/--max-size.

In the original implementation in #5370, the virtual display size was
necessarily the same as the capture size. The --max-size value was only
allowed to determine the virtual display size when no explicit size was
provided.

Since the dpi was scaled down accordingly, it is often better to create
a virtual display at the target capture size directly. However, not
everything is rendered according to the virtual display DPI. For
example, a page in Firefox is rendered too big on small virtual
displays. Thus, it makes sense to be able create a virtual display at a
given size, and capture it at a lower resolution with --max-size. This
is now possible using OpenGL filters.

Therefore, change the behavior of --max-size for virtual displays:
 - it does not impact --new-display without size argument anymore (the
   virtual display size is the main display size);
 - it is used to limit the capture size (whether an explicit size is
   provided or not).

This new behavior is consistent with main display capture.

Refs #5370 comment <https://github.com/Genymobile/scrcpy/pull/5370#issuecomment-2438944401>
Refs <https://github.com/Genymobile/scrcpy/pull/5370>

app/scrcpy.1

@@ -318,14 +318,13 @@ Disable video and audio playback on the computer (equivalent to \fB\-\-no\-video
 
 .TP
 \fB\-\-new\-display\fR[=[\fIwidth\fRx\fIheight\fR][/\fIdpi\fR]]
-Create a new display with the specified resolution and density. If not provided, they default to the main display dimensions and DPI, and \fB\-\-max\-size\fR is considered.
+Create a new display with the specified resolution and density. If not provided, they default to the main display dimensions and DPI.
 
 Examples:
 
     \-\-new\-display=1920x1080
     \-\-new\-display=1920x1080/420
     \-\-new\-display         # main display size and density
-    \-\-new\-display -m1920  # scaled to fit a max size of 1920
     \-\-new\-display=/240    # main display size and 240 dpi
 
 .TP

app/src/cli.c

@@ -590,12 +590,11 @@ static const struct sc_option options[] = {
         .optional_arg = true,
         .text = "Create a new display with the specified resolution and "
                 "density. If not provided, they default to the main display "
-                "dimensions and DPI, and --max-size is considered.\n"
+                "dimensions and DPI.\n"
                 "Examples:\n"
                 "    --new-display=1920x1080\n"
                 "    --new-display=1920x1080/420  # force 420 dpi\n"
                 "    --new-display         # main display size and density\n"
-                "    --new-display -m1920  # scaled to fit a max size of 1920\n"
                 "    --new-display=/240    # main display size and 240 dpi",
     },
     {
@@ -2891,13 +2890,6 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
             LOGE("--new-display is incompatible with --no-video");
             return false;
         }
-
-        if (opts->max_size && opts->new_display[0] != '\0'
-                           && opts->new_display[0] != '/') {
-            // An explicit size is defined (not "" nor "/<dpi>")
-            LOGE("Cannot specify both --new-display size and -m/--max-size");
-            return false;
-        }
     }
 
     if (otg) {

doc/video.md

@@ -193,9 +193,9 @@ phone, landscape for a tablet).
 
 Cropping is performed before `--capture-orientation` and `--angle`.
 
-For screen mirroring, `--max-size` is applied after cropping. For camera and
+For display mirroring, `--max-size` is applied after cropping. For camera,
-virtual display mirroring, `--max-size` is applied first (because it selects the
+`--max-size` is applied first (because it selects the source size rather than
-source size rather than resizing it).
+resizing the content).
 
 
 ## Display

doc/virtual_display.md

@@ -8,7 +8,6 @@ To mirror a new virtual display instead of the device screen:
 scrcpy --new-display=1920x1080
 scrcpy --new-display=1920x1080/420  # force 420 dpi
 scrcpy --new-display         # use the main display size and density
-scrcpy --new-display -m1920  # ... scaled to fit a max size of 1920
 scrcpy --new-display=/240    # use the main display size and 240 dpi
 ```
 

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

@@ -60,7 +60,7 @@ public final class Size {
      * @return The current size rounded.
      */
     public Size round8() {
-        if ((width & 7) == 0 && (height & 7) == 0) {
+        if (isMultipleOf8()) {
             // Already a multiple of 8
             return this;
         }
@@ -80,6 +80,10 @@ public final class Size {
         return new Size(w, h);
     }
 
+    public boolean isMultipleOf8() {
+        return (width & 7) == 0 && (height & 7) == 0;
+    }
+
     public Rect toRect() {
         return new Rect(0, 0, width, height);
     }

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

@@ -48,7 +48,7 @@ public class NewDisplayCapture extends SurfaceCapture {
 
     private Size mainDisplaySize;
     private int mainDisplayDpi;
-    private int maxSize; // only used if newDisplay.getSize() != null
+    private int maxSize;
     private final Rect crop;
     private final boolean captureOrientationLocked;
     private final Orientation captureOrientation;
@@ -101,7 +101,7 @@ public class NewDisplayCapture extends SurfaceCapture {
         int displayRotation;
         if (virtualDisplay == null) {
             if (!newDisplay.hasExplicitSize()) {
-                displaySize = mainDisplaySize.limit(maxSize).round8();
+                displaySize = mainDisplaySize;
             }
             if (!newDisplay.hasExplicitDpi()) {
                 dpi = scaleDpi(mainDisplaySize, mainDisplayDpi, displaySize);
@@ -128,10 +128,19 @@ public class NewDisplayCapture extends SurfaceCapture {
         filter.addOrientation(displayRotation, captureOrientationLocked, captureOrientation);
         filter.addAngle(angle);
 
+        Size filteredSize = filter.getOutputSize();
+        if (!filteredSize.isMultipleOf8() || (maxSize != 0 && filteredSize.getMax() > maxSize)) {
+            if (maxSize != 0) {
+                filteredSize = filteredSize.limit(maxSize);
+            }
+            filteredSize = filteredSize.round8();
+            filter.addResize(filteredSize);
+        }
+
         eventTransform = filter.getInverseTransform();
 
         // DisplayInfo gives the oriented size (so videoSize includes the display rotation)
-        videoSize = filter.getOutputSize().limit(maxSize).round8();
+        videoSize = filter.getOutputSize();
 
         // But the virtual display video always remains in the origin orientation (the video itself is not rotated, so it must rotated manually).
         // This additional display rotation must not be included in the input events transform (the expected coordinates are already in the
@@ -231,11 +240,6 @@ public class NewDisplayCapture extends SurfaceCapture {
 
     @Override
     public synchronized boolean setMaxSize(int newMaxSize) {
-        if (newDisplay.hasExplicitSize()) {
-            // Cannot retry with a different size if the display size was explicitly provided
-            return false;
-        }
-
         maxSize = newMaxSize;
         return true;
     }

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

@@ -103,4 +103,17 @@ public class VideoFilter {
         double ccwAngle = -cwAngle;
         transform = AffineMatrix.rotate(ccwAngle).withAspectRatio(size).fromCenter().multiply(transform);
     }
+
+    public void addResize(Size targetSize) {
+        if (size.equals(targetSize)) {
+            return;
+        }
+
+        if (transform == null) {
+            // The requested scaling is performed by the viewport (by changing the output size), but the OpenGL filter must still run, even if
+            // resizing is not performed by the shader. So transform MUST NOT be null.
+            transform = AffineMatrix.IDENTITY;
+        }
+        size = targetSize;
+    }
 }