WindowServer: Support windows with alpha channels. And per-WSWindow opacity.

This patch also adds a Format concept to GraphicsBitmap. For now there are
only two formats: RGB32 and RGBA32. Windows with alpha channel have their
backing stores created in the RGBA32 format.

Use this to make Terminal windows semi-transparent for that comfy rice look.
There is one problem here, in that window compositing overdraw incurs
multiple passes of blending of the same pixels. This leads to a mismatch in
opacity which is obviously not good. I will work on this in a later patch.

The alpha blending is currently straight C++. It should be relatively easy
to optimize this using SSE instructions.

For now I'm just happy with the cute effect. :^)

1 files changed, 4 insertions, 3 deletions

diff --git a/WindowServer/WSWindow.cpp b/WindowServer/WSWindow.cpp
index 8e440e1ec8..61e9073123 100644
--- a/WindowServer/WSWindow.cpp
+++ b/WindowServer/WSWindow.cpp
@@ -44,9 +44,10 @@ void WSWindow::set_rect(const Rect& rect)
     m_rect = rect;
     if (!m_backing || old_rect.size() != rect.size()) {
         if (m_menu)
-            m_backing = GraphicsBitmap::create(m_rect.size());
-        else if (m_client)
-            m_backing = m_client->create_shared_bitmap(m_rect.size());
+            m_backing = GraphicsBitmap::create(GraphicsBitmap::Format::RGB32, m_rect.size());
+        else if (m_client) {
+            m_backing = m_client->create_shared_bitmap(m_has_alpha_channel ? GraphicsBitmap::Format::RGBA32 : GraphicsBitmap::Format::RGB32, m_rect.size());
+        }
 
     }
     WSWindowManager::the().notify_rect_changed(*this, old_rect, rect);