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Version 38 (modified by davea, 10 years ago) (diff)
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Providing graphics for BOINC applications

Providing graphics for BOINC applications

A BOINC application may provide graphics (e.g. visualizations) to volunteers. These graphics are shown in two contexts:

As a screensaver, if selected by the user.
In a window, opened using the Show Graphics button in the BOINC Manager.

Graphics apps

Graphics are generated by a 'graphics app' program (separate from the main application). This graphics app must have the properties that:

If invoked with --fullscreen, it opens a full-screen borderless window. It must exit on mouse or keyboard input (if you use the BOINC graphics API library this is handled automatically).
Otherwise it opens a standard window, and may handle mouse/keyboard input.

The logical name of the program must be 'graphics_app'. When you set up your application version directory, use an entry like

<file>
   <physical_name>uppercase_graphics_6.14_windows_intelx86.exe</physical_name>
   <logical_name>graphics_app</logical_name>
</file>

in your version.xml file.

The graphics app is launched by the BOINC Manager and/or by the screensaver. It may be killed at any time. Multiple instances of the graphics app may run at the same time (e.g. if the user opens a graphics window via the Manager, and then the screensaver runs and launches another instance).

The BOINC graphics API provides cross-platform support for developing graphics apps.

A complete example can be found in boinc/samples/example_app.

The BOINC Graphics API

BOINC supplies a library (libboinc_graphics2.a) with support for graphics apps. To use this library, the graphics app must call

boinc_graphics_loop(int argc, char** argv);

after its initialization. This function executes an event loop, and does not return.

The application must supply the following functions:

void app_graphics_init();

Called once, after the window has been created.

void app_graphics_render(int xs, ys, double time_of_day);

This will be called periodically. It should generate the current graphic. xs and ys are the X and Y sizes of the window, and time_of_day is the relative time in seconds.

void app_graphics_resize(int x, int y);

Called when the window size changes.

void boinc_app_mouse_move(
    int x, int y,       // new coords of cursor
    int left,          // whether left mouse button is down
    int middle,
    int right
);

void boinc_app_mouse_button(
    int x, int y,       // coords of cursor
    int which,          // which button (0/1/2)
    int is_down        // true iff button is now down
);

void boinc_app_key_press(
    int, int            // system-specific key encodings
)

void boinc_app_key_release(
    int, int            // system-specific key encodings
)

Communication between main and graphics apps

The graphics app may want to get information from the main app. This can be done using either shared memory or a file.

Shared memory

Communicating large amounts of data can be done efficiently using shared memory. The BOINC library supplies the following functions to facilitate this:

void* boinc_graphics_make_shmem(char* appname, int size);

Called from the main app. Creates a shared memory segment of the given size.

'appname' should be the name of this application (used to ensure uniqueness of the shared-memory segment name).

void* boinc_graphics_get_shmem(char* appname);

Called from the graphics app. Attaches to an existing segment. It must be called AFTER boinc_parse_init_data_file().

The contents of the shared memory segment are application-dependent; typically it contains numeric information describing the state of the computation.

You may want to include the following items:

struct UC_SHMEM {
    double update_time;
    double fraction_done;
    double cpu_time;
    BOINC_STATUS status;
    int countdown;
};

These items should be updated by the main app once per second, using boinc_set_timer_handler(). The items are:

update_time: The current time (dtime()). The graphics app should exit if the current time exceeds this by 5 seconds or so, so that it exits if the main app exits.
fraction_done: The last fraction done reported by the main app.
cpu_time: The current CPU time, as returned by boinc_worker_thread_cpu_time().
status: The BOINC status, as returned by boinc_get_status(). If the 'suspended' flag is set, the graphics app should stop changing its display, and instead show an "application suspended" message.
countdown: See below.

Keep in mind that multiple instances of the graphics app may run simultaneously; avoid having the graphics app write to the shared memory. If you use shared memory to store a data structure, use a semaphore to synchronize access so that the graphics app doesn't see an inconsistent state.

Updating the shared memory structure uses CPU time, and it's desirable to avoid this overhead if no graphics app is running.

One way to do this is to include a countdown field in the shared memory structure, as above.

The graphics sets this to 5 (say) in its app_graphics_render() function.
The main app decrements this (if positive) once per second.
The main app updates the application-specific data in shared memory only when countdown is nonzero.

See the example application for an example.

File

Alternatively, you can communicate data from main app to graphics app via a file. The BOINC library provides two functions for this purpose. The main program can call

int boinc_write_graphics_status(
    const char* filename, double cpu_time, double elapsed_time,
    double fraction_done
);

to write a file containing its status in XML format. The graphics app can call

int boinc_parse_graphics_status(
    const char* filename, double* update_time, double* cpu_time,
    double* elapsed_time, double* fraction_done, BOINC_STATUS* status
);

to read and parse this file.

Creating an icon for your applications

For Windows:

make Icons (there's a tool for this in Visual Studio), say "boincAppIcon16x16.ico", "boincAppIcon32x32.ico" and "boincAppIcon48x48.ico".
create a simple resource description file "boincAppIcon.rc" in the same directory as the icon files pointing to the icon filenames, the first entry is the resource name that is later passed to setWinIcon():
```
boinca16 ICON boincAppIcon16x16.ico
boinca32 ICON boincAppIcon32x32.ico
boinca48 ICON boincAppIcon48x48.ico
```
compile the resource (I do this on a Visual Studio Command Prompt):
```
rc.exe boincAppIcon.rc
```
when linking the App, add the resulting file boincAppIcon.RES to the objects

we call setWinIcon("boinca16","boinca48") in app_graphics_init()

Support classes

Several graphics-related classes were developed for SETI@home. They may be of general utility.

TEXTURE_DESC

Represents a JPEG image displayed in 3 dimensions.

PROGRESS and PROGRESS_2D

Represent progress bars, depicted in 3 or 2 dimensions.

REDUCED_ARRAY

Represents a two-dimensional array of data, which is reduced to a smaller dimension by averaging or taking extrema. Includes member functions for drawing the reduced data as a 3D graph in several ways (lines, rectangles, connected surface).

RIBBON_GRAPH

Represents of 3D graph of a function of 1 variable.

MOVING_TEXT_PANEL

Represents a flanged 3D panel, moving cyclically in 3 dimensions, on which text is displayed.

STARFIELD

Represents a set of randomly-generated stars that move forwards or backwards in 3 dimensions.

The file api/ttfont.cpp has support functions from drawing nice-looking 3D text.

Displaying a static image

An application can display a pre-existing JPEG file as its graphic. This is the simplest approach since you don't need to develop any code. You must include the image file with each workunit. To do this, link the application with api/static_graphics.cpp (edit this file to use your filename). You can change the image over time, but you must change the (physical, not logical) name of the file each time.

Using Web graphics

You can also generate graphics using HTML. Note: this works for graphics windows created using the Manager's Show Graphics button; it doesn't provide a screensaver.

In this case your main program supplies a URL that supplies the HTML. This may be an external URL, or it may refer to a web server embedded in your main program (i.e. a URL of the form http://localhost:port). Your main program can call

boinc_web_graphics_url(char* url)

to register a URL to be used for graphics; in this case, the BOINC Manager's Show Graphics button will open a Web browser window to this URL.

Displaying text

BOINC supports the display of text using TrueType fonts.

Add the files api/ttfont.cpp and api/ttfont.h to your application (they are not included in any BOINC library.)
Link with the FreeType2 and FTGL libraries. Depending on how you build the FreeType2 library, FreeType2 may require the libz and libbz2 libraries. For Windows, prebuilt libraries are available in the boinc_depends_win_vs2005 repository. To build these libraries on the Mac, please see MacBuild.
Include the desired TrueType fonts in your app versions. The set of free Liberation fonts in included the api/ttf/ directory. If you wish to use other TrueType fonts, you'll need to adjust the list of font names in ttfont.cpp. (Another source of free fonts is the GNU Freefont project.)

To display text, use the following API functions:

float white[4] = {1., 1., 1., 1.};
APP_INIT_DATA aid;
boinc_get_init_data(aid);

// read font files; they're in the project directory
//
ttf_load_fonts(aid.project_dir);
...
ttf_render_string(
   x, y, z,            // where to display string
   500,                // size
   white,              // color
   "App suspended"     // the text
   0,                  // which font (see ttfont.cpp)
                       // default is Sans-Regular (0)
);

Other parameters to ttf_render_string() let you specify rotation; see ttfont.h. For examples, see the clientscr/ss_app.cpp and samples/exampple_app/uc2_graphics.cpp in the BOINC trunk.

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