Question

We’re trying to port a C++ application to Android. We think that using NativeActivity should be easiest, and let all OpenGL/EGL-stuff be done natively.

Right now, we’re passing the ANativeWindow-pointer that we get from the android_app struct in android_native_app_glue.h through the application so that it can be used when the window is initialized. Here’s a few relevant lines from this code (stripped from debug-code):

bool OpenGLWindowES::Initialize(EGLNativeWindowType wnd, EGLNativeDisplayType dsp,
                            EGLint redSize, EGLint greenSize, EGLint blueSize, EGLint             alphaSize, EGLint depthSize, bool bMultiSample)
{
    m_display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    if(m_display == EGL_NO_DISPLAY)
    {
        return false;
    }

    EGLint iMajorVersion, iMinorVersion;
    if (!eglInitialize(m_display, &iMajorVersion, &iMinorVersion))
    {
        return false;
    }

    eglBindAPI(EGL_OPENGL_ES_API);
    bool ecc = eglChooseConfig(m_display, attribs, &m_config, 1, &iConfigs);
    if (!ecc || (iConfigs != 1))
    {
        return false;
    }

    EGLint format;
    eglGetConfigAttrib(m_display, m_config, EGL_NATIVE_VISUAL_ID, &format);
    ANativeWindow_setBuffersGeometry(wnd, 0, 0, format);
    m_windowSurface = eglCreateWindowSurface(m_display, m_config, wnd, NULL);
    //etc
}    

This code proceeds with creating a context, makecurrent etc, but we don’t get that far. We get a segmentation fault on eglCreateWindowSurface and since the display and config seem to be initialized correctly, this can only mean a problem with the ANativeWindow* (tyepdef’d to a EGLNativeWindowType). Error message:

signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 00000058

We also get a segmentation fault if we call for example:

ANativeWindow_getHeight(wnd);

So the question is, what can cause a segmentation fault at this point? wnd is not null, we’ve checked this before, so it should be initalized somehow and should be ready to use. Did we miss something before calling this function, or can there be some problem with the pointer?

EDIT: We’re currently wondering if this can have something to do with the APP_CMD_INIT_WINDOW command not being sent or received properly (we haven’t implemented any command handling at all yet so we’re looking into this).

Answer 1

Are you entirely sure that the window is correctly initialized?

The ANativeWindow pointer in the app struct is not automatically set when passed into the native entry point. It is provided by the main Android thread at a later point and will then be sent to the app via the callback system that app_glue has set up.

You need to handle the calls sent to the android_app yourself, in the native_activity example in the NDK they do it like this:

int ident;
int events;
struct android_poll_source* source;

// If not animating, we will block forever waiting for events.
// If animating, we loop until all events are read, then continue
// to draw the next frame of animation.
while ((ident=ALooper_pollAll(engine.animating ? 0 : -1, NULL, &events,
        (void**)&source)) >= 0) {

    // Process this event.
    if (source != NULL) {
        source->process(state, source);
    }
    ....
}

You probably need something like this in your main rendering loop, this will allow app_glue to automatically set the window correctly when it gets it from the main thread.