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howie_007

Stencil buffer not working on Android NDK implementation

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Got my game engine to build and run on the Android over the week end. It also builds and runs on Windows and Linux.

 

Is there some extra step to get stencil buffering working? Same code works as expected on WIndows and Linux.

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Thanks frob but I found the problem (face palm).

 

I was setting glStencilMask() before and after the render to the stencil buffer. I found some info about how this should be set before the stencil buffer is cleared and in many cases, only needs to be set in your init with all your other OpenGL settings on start up.

 

My implementation was from some stencil buffer demo but worked fine in WIndows and Linux. Odd.

Edited by GameCodingNinja

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i will be using stencil in future, can you tell more about it? are you only setting stencil bits during opengl initialization, or did you write something else?

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I'm only setting it in the init now. My stencil needs at the moment are very simple but I can't see needing to do more at this time.

 

The way to think of this is the glStencilMask() is like glClearColor, you're telling OpenGL what value to use when clearing the stencil buffer, just like the color or depth buffer. This all happens when glClear is used. Example: glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT )

 

See my adjusted code below.

/************************************************************************
*    desc:  Init the game
************************************************************************/
void CBaseGame::Init()
{
    // Init the clear color
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    
    // Init the stencil clear mask based on the bit size of the mask
    // Stencil buffer can only be 1 or 8 bits per pixel
    if( CSettings::Instance().GetStencilBufferBitSize() == 1 )
        glStencilMask(0x1);
    else if( CSettings::Instance().GetStencilBufferBitSize() == 8 )
        glStencilMask(0xff);

    // Cull the back face
    glFrontFace(GL_CCW);
    glCullFace(GL_BACK);
    glEnable(GL_CULL_FACE);

    // Enable alpha blending
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    // Make the zero texture the active texture
    glActiveTexture(GL_TEXTURE0);

    // Show the window
    CDevice::Instance().ShowWindow( true );

    if( CSettings::Instance().GetClearTargetBuffer() )
        m_clearBufferMask |= GL_COLOR_BUFFER_BIT;

    if( CSettings::Instance().GetEnableDepthBuffer() )
        m_clearBufferMask |= GL_DEPTH_BUFFER_BIT;
    
    if( CSettings::Instance().GetClearStencilBuffer() )
        m_clearBufferMask |= GL_STENCIL_BUFFER_BIT;
    
    // Display a black screen
    glClear( GL_COLOR_BUFFER_BIT );
    SDL_GL_SwapWindow( m_pWindow );

}   // Init

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