AudioServer: Allow muting the system audio

This patch adds muting to ASMixer, which works by substituting what we
would normally send to the sound card with zero-filled memory instead.
We do it this way to ensure that the queued sample buffers keep getting
played (silently.)

This is obviously not the perfect way of doing this, and in the future
we should improve on this, and also find a way to utilize any hardware
mixing functions in the sound card.

1 files changed, 24 insertions, 13 deletions

diff --git a/Servers/AudioServer/ASMixer.cpp b/Servers/AudioServer/ASMixer.cpp
index 15a317e4a4..2cd71e8bec 100644
--- a/Servers/AudioServer/ASMixer.cpp
+++ b/Servers/AudioServer/ASMixer.cpp
@@ -15,6 +15,8 @@ ASMixer::ASMixer()
         return;
     }
 
+    m_zero_filled_buffer = (u8*)malloc(4096);
+    bzero(m_zero_filled_buffer, 4096);
     m_sound_thread.start();
 }
 
@@ -66,33 +68,42 @@ void ASMixer::mix()
             }
         }
 
+        bool muted = m_muted;
+
         // output the mixed stuff to the device
         u8 raw_buffer[4096];
-        auto buffer = ByteBuffer::wrap(raw_buffer, sizeof(raw_buffer));
-        BufferStream stream(buffer);
+        auto buffer = ByteBuffer::wrap(muted ? m_zero_filled_buffer : raw_buffer, sizeof(raw_buffer));
 
-        for (int i = 0; i < mixed_buffer_length; ++i) {
-            auto& mixed_sample = mixed_buffer[i];
+        BufferStream stream(buffer);
+        if (!muted) {
+            for (int i = 0; i < mixed_buffer_length; ++i) {
+                auto& mixed_sample = mixed_buffer[i];
 
-            mixed_sample.scale(m_main_volume);
-            mixed_sample.clip();
+                mixed_sample.scale(m_main_volume);
+                mixed_sample.clip();
 
-            i16 out_sample;
-            out_sample = mixed_sample.left * std::numeric_limits<i16>::max();
-            stream << out_sample;
+                i16 out_sample;
+                out_sample = mixed_sample.left * std::numeric_limits<i16>::max();
+                stream << out_sample;
 
-            ASSERT(!stream.at_end()); // we should have enough space for both channels in one buffer!
-            out_sample = mixed_sample.right * std::numeric_limits<i16>::max();
-            stream << out_sample;
+                ASSERT(!stream.at_end()); // we should have enough space for both channels in one buffer!
+                out_sample = mixed_sample.right * std::numeric_limits<i16>::max();
+                stream << out_sample;
+            }
         }
 
         if (stream.offset() != 0) {
             buffer.trim(stream.offset());
-            m_device->write(buffer);
         }
+        m_device->write(buffer);
     }
 }
 
+void ASMixer::set_muted(bool muted)
+{
+    m_muted = muted;
+}
+
 ASBufferQueue::ASBufferQueue(ASClientConnection& client)
     : m_client(client.make_weak_ptr())
 {