Using two QGLShaderProgram for objects in a same 3D scene [SOLVED]



  • Hello,

    i have this very weird behaviour happening here. I have two different QGLShaderProgram objects in my application, a 3D scene containing 2 objects is drawn in the paintGL method. I'm using program1 to draw object1, qnd program2 to draw object2 like this:
    @
    paintGL()
    {

    program1->bind();
    drawObject1();

    program2->bind()
    drawObject2();

    }
    @
    Then object1 is correctly drawn, but nothing is drawn for object2.
    If I invert the programs but not the object drawing order like this:

    @
    paintGL()
    {

    program2->bind();
    drawObject1();

    program1->bind()
    drawObject2();

    }
    @

    then object1 is drawn with program 2, but object2 is still not drawn at all.

    If I simply want to draw object2 only, using either program1 or program2, then object2 is perfectly drawn.

    Anybody has an idea of what my problem could be?
    And yes i tried to debug the code, but when pressing F11 on the bind line, then no source code shows up, I have recompiled Qt twice with -debug option, but nothing will do.

    Thank you for your help,
    Bill

    Edit: please use @ tags for code sections; Andre



  • Does the drawObject1() function leave the the GL state in the state expected by drawObject2(). For example are you applying some transformation without pushing/popping the matrix stack correctly?



  • Hello ZapB,

    It actually does, so I think, because if I run this:
    @
    paintGL()
    {

    program1->bind();
    drawObject1();

    program2->bind()
    drawObject2();

    program1->bind()
    drawObject3();

    }
    @
    Then object 3, is drawn correctly! Driving me mad, for sure! :)



  • OK does this work?

    @
    paintGL()
    {
    program1->bind();
    drawObject1();

    program2->bind()
    drawObject3();
    

    }
    @



  • in this case I will see object1, but not object3, :)



  • Hmmm, OK then. Could you post a small compilable example that shows the problem please so that we can take a look on our own machines? The simpler the better.



  • I wish I could, but my program is huge!
    I could try to make a simpler one though, but at least you seem to agree that my way of thinking is correct by calling the bind method twice in the same paintGL call to use different programs for different objects in my scene, right?

    now I tried to recompiled Qt (Windows XP) to be able to get the bind source code to show up when I press F11, but now I can't even recompile my entire code. The link is failing with this message:

    g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -mthreads -Wl -Wl,-subsystem,windows -o debug\ws2.exe object_script.ws2.Debug -L"d:_Personal\Progz\Qt\Qt472\lib" -lglu32 -lopengl32 -lgdi32 -luser32 -lmingw32 -lqtmaind -lQtOpenGLd4 -lQtGuid4 -lQtCored4
    mingw32-make[1]: Leaving directory D:/_Work/QTProjectsDir/WS2-build-desktop' mingw32-make: Leaving directoryD:/_Work/QTProjectsDir/WS2-build-desktop'
    d:/_personal/progz/qt/qtcreator_21/mingw/bin/../lib/gcc/mingw32/4.4.0/../../../../mingw32/bin/ld.exe: cannot find -lQtOpenGLd4
    collect2: ld returned 1 exit status
    mingw32-make[1]: *** [debug\ws2.exe] Error 1
    mingw32-make: *** [debug] Error 2
    The process "D:_Personal\Progz\Qt\qtcreator_21\mingw\bin\mingw32-make.exe" exited with code 2.
    Error while building project ws2 (target: Desktop)
    When executing build step 'Make'



  • The reason I asked for a small example is that often the action of producing such an example actually allows you to find the bug yourself whilst going through the process.

    Just make a simple class that inherits QGLWidget, provide a coule of very simply drawObjectN() functions and some simple shaders. See if that reproduces the problem. If it does then we can help, if not then the problem is elsewhere in your code but at least we'll know we need to dig deeper and see more of your code.

    Wrt to your linker error, does QtOpenGLd4.lib exist on your system where the linker is looking for it?



  • Yes I agree with your statement and the small openGL program.

    Concerning my new link issue:
    I actually just recompile Qt several times :
    first by calling configure -debug -opengl desktop -> but then the compilation of my application failed because it tried to open a GLES2 directory,
    so I restart by calling
    configure -debug -es2, but I got the same issue,
    i called make distclean which partially failed,
    and then recalled
    configure -debug, and since then I have this link error.
    I know I suck ;)



  • Before reconfiguring Qt, try doing:

    @make confclean@

    I'll keep an eye out for your example.



  • Thanks ZapB



  • Hey ZapB,
    My first use-case was actually wrong, I spent a lot of time on this, and the use cases are as follow:
    @
    paintGL()
    {

    program1->bind();
    drawObject1();

    program2->bind()
    drawObject2();

    drawObject3();

    }

    then object 1 is drawn using program 1, and object 2 and object 3 are drawn using program 2. which is fine!
    But now I have this other use case causing the issue:

    paintGL()
    {

    program1->bind();
    drawObject1();

    program2->bind()
    drawObject2();

    program1->bind()
    drawObject3();

    }
    @
    then object 1 and object 3 are drawn using program1, whereas object 2 is not drawn at all.

    It looks like the fact to return to another program (program1) before the end of paintGL function would sort of invalidate the drawing made by program2. Maybe I should add some method to force the rendering in program2, before swapping back to program1?



  • I tried to add some glFinish, and/or glEnd before swapping programs, but none of them helped in anyway to get my object 2 drawn.... Yes, I am Desperate!



  • Have you got anywehere with preparing the simple example yet?



  • Yes i have a very simple source code to send for you this afternoon.
    Bill



  • Hello ZapB how do I send yo my source code? it's a zip file. is it possible to send it to you by mail or something?



  • error



  • In the meantime you can download it from here:
    http://www.mediafire.com/?bdejk5y93gr3wqv

    In the draw function, you will see there are four different UseCases, you can use the "define" preprocessor directive to activate each one, and see the problems occuring,

    Thank you,
    Bill



  • Hello ZapB, did you have time to test my source code?
    Thank you,
    Bill



  • I managed to get it built yesterday but when I ran it I got some error complaining about one of your shaders not defining some variable as a varying. I can't recall which it was at the moment. I am really busy today so I'll try to take a proper look tomorrow.



  • In the myWidget.cpp file, you can choose three different options declared as defines.
    #define PC_BILL , #define PC_WORK, #define TARGET_IMX
    maybe you can switch between the two firsts (either PC_BILL, or PC_WORK), and see if your vertex compiles alright then.
    I have this workshop forecast on monday, it could be nice if I can solve the issue before if you are able to help me ;)

    Thank you,
    Bill



  • Hello, anybody?



  • Hey, I got your program compiled using BILL definition. The output of the program:
    myWidget::myWidget parent WinID = 0x80650
    BILL : InitializeGL
    Vertex Shader compiled OK ""
    Fragment Shader compiled OK ""
    Program 3 linked OK ""
    Vertex Shader compiled OK ""
    Fragment Shader compiled OK ""
    Program 6 linked OK ""
    BILL : ResizeGL
    BILL : myWidget instance : myWidget(0x9ba6f18)
    model draw
    Error 1282 myWidget.cpp 436
    model draw
    model draw
    model draw
    BILL : myWidget ~myWidget
    BILL : myWidget instance : myWidget(0x9ba6f18)

    As visual, I saw three identical green triangles.

    I dunno if this helps any, I need to dive into shader programs and source code to deeply analyze what the shaders are supposed to do, and are they doing what they are suppose to :)

    edit: forgot to say that this output was from USE_CASE1. Running now the rest of them.

    edit2: Ran the rest of the use cases and got indeed some missing triangles, now digging into the code :)



  • Sorry for the delay on this. I'll try to take another look this weekend too.



  • Found the problem:

    When you set uniform values like this:
    @
    g_hProjMatrixLoc = qGLShaderProgramTextures->uniformLocation("g_matProj");
    qGLShaderProgramTextures->setUniformValue(g_hProjMatrixLoc, matProj3);
    @
    you have to have your shaderprogram binded to current context with
    @
    qGLShaderProgramTextures->bind()
    @
    before modifying uniforms.

    Also a tip:
    the two clauses above can be replaced with one:
    @
    qGLShaderProgramTextures->setUniformValue("g_matProj", matProj3);
    @
    where it uses uniform name directly.

    Of course if you want to save your uniform location for later use, then the tip is useless :)

    edited to format code blocks.



  • matrixx: Well spotted and it applies to the other matrices too.

    The fix is to change your paintGL() function to this:

    @
    void myWidget::paintGL()
    {
    /prepare projection matrix, only once!/
    static bool loop = 1;
    static GLfloat matProj3[4][4];
    if (loop == 1)
    {
    memset (matProj3, 0, 16*sizeof(GLfloat));
    matProj3[0][0] = 2;
    matProj3[1][1] = matProj3[0][0] * g_fAspectRatio;
    matProj3[2][2] = -1.0f;
    matProj3[2][3] = -1.0f;
    matProj3[3][2] = -1.0f;
    loop = 0;
    }

    // Clear the colorbuffer and depth-buffer
    QColor bgColor(10,15,255,255);
    qglClearColor( bgColor );
    DEBUGBILL
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    DEBUGBILL
    
    qGLShaderProgramTextures->bind();
    g_hProjMatrixLoc = qGLShaderProgramTextures->uniformLocation("g_matProj");
    qGLShaderProgramTextures->setUniformValue(g_hProjMatrixLoc, matProj3);
    
    qGLShaderProgramScreen->bind();
    g_hProjMatrixLoc = qGLShaderProgramScreen->uniformLocation("g_matProj");
    qGLShaderProgramScreen->setUniformValue(g_hProjMatrixLoc, matProj3);
    
    QMatrix4x4 tempRot(+cosf( fAngle ),0,-sinf( fAngle ),0,
                       0,1,0,0,
                       +sinf( fAngle ) ,0,+cosf( fAngle ),0,
                       0,0,0,1.0);
    
    GLuint g_hSamplerLoc = 0;
    qGLShaderProgramTextures->bind();
    g_hSamplerLoc = qGLShaderProgramTextures->uniformLocation("g_matModelView");
    qGLShaderProgramTextures->setUniformValue(g_hSamplerLoc, tempRot);
    
    qGLShaderProgramScreen->bind();
    g_hSamplerLoc = qGLShaderProgramScreen->uniformLocation("g_matModelView");
    qGLShaderProgramScreen->setUniformValue(g_hSamplerLoc, tempRot);
    
    drawTest();
    

    }
    @

    The reason it worked for the different shaders depending which one was drawn first is beause your were not properly restoring which shader was bound each time around the rendering loop. Now they are explicitly set.

    As an aside this type of thing is much easier to spot if you use a consistent coding style. I can spot at least two different coding styles in this file.



  • matrixx and ZapB YOU ARE GENIOUS! Thank you so much for this, I really didn't know this, but of course the more I progress in openGL the more this error is made obvious.
    THANK YOU!!!



  • we can lock this thread now of course!



  • Thread closing is not neccessary (because there can be other people who will have similar problem later). But marking as [solved] will be good, don't forget to do it.


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