2011-9-17 21:20:56

 

2011-9-17 21:20:56

 
  The Android-specific header 'framebuffer.h' is used to provide a generic interface between framebuffer 'producers' and 'clients'.
   Essentially, each QFrameBuffer object:
    - holds a contiguous pixel buffer allocated by the emulator.
    - can have one producer in charge of drawing into the pixel buffer
    - can have zero or more clients, in charge of displaying the pixel buffer to the final UI window (or remote VNC connection, whatever).
  The emulator will periodically call 'qframebuffer_check_updates()' which does the following:
 
  qframebuffer_check_updates
 
  foreach fb in framebuffers:
   if fb.producer:
    fb.producer.check_updates() => in producer foreach up in
   
     updates: qframebuffer_update(fb, up.x, up.y, up.w, up.h) => foreach cl in fb.clients: cl.update(cl.opaque, up.x, up.y. up.w, up.h)
 
  hw/goldfish_fb.c implements a producer
  the QEmulator type in android/main.c implements a client.

 
struct goldfish_fb_state {
    struct goldfish_device dev;
    QFrameBuffer*  qfbuff;
    uint32_t fb_base;
    uint32_t base_valid : 1;
    uint32_t need_update : 1;
    uint32_t need_int : 1;
    uint32_t set_rotation : 2;
    uint32_t blank : 1;
    uint32_t int_status;
    uint32_t int_enable;
    int      rotation;   /* 0, 1, 2 or 3 */
};

 

 

3 - DisplayState (console.h):
-----------------------------
  The upstream QEMU sources use a DisplayState object to model the state of each "display".
   This is not conceptually exactly the same thing than a QFrameBuffer object as it can also be used to emulated text-based displays instead of pixel framebuffers,
  
    and incorporates input state
  as well.
  See sdl_display_init() in android/main.c which is called from vl-android.c on startup to initialize the display. This really registers a function, sdl_refresh()
 
  (in android/main.c), that will get called every 1/60th of a second to handle pending inputs.
 
 
  sdl_refresh() also calls qframebuffer_check_updates(), ensuring that any animation in the emulated framebuffer will be displayed at the same frequency.
  The refresh frequency is defined by the GUI_REFRESH_INTERVAL defined at the top of console.h
4 - QEmulator object:
---------------------
  Currently defined and implemented in android/main.c (we may want to move it to a different location). The QEmulator object bridges provides a framebuffer client
 
   that uses the "generic" skin code under android/skin to display the main UI window.
  
  
   qframebuffer_check_updates
  
  
   Android Framebuffer emulation technical notes: ==============================================
This document tries to explain how framebuffer emulation works in the Android emulator.
1 - Hardware emulation (hw/goldfish_fb.c):
------------------------------------------
  The emulated hardware provides a bunch of i/o registers to allow
  the following:
  - let the kernel query the framebuffer's dimensions (both in pixels and millimeters) (see goldfish_fb_read)
  - let the kernel control the physical base address for the framebuffer and the internal pixel rotation to apply before display (see goldfish_fb_write).
  The pixel buffer is itself a set of physical pages allocated by the kernel driver in the emulated system. These pages are contiguous in
  the emulated system, but not in the emulator's process space which places them randomly in the heap.
  Also, a function called goldfish_fb_update_display() is in charge of checking the dirty bits of the framebuffer physical pages, in order to compute the bounding rectangle of pixel updates since the last call, and send them to the UI through qframebuffer_update(). More on this later.
2 - Framebuffer abstract interface (framebuffer.h):
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