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Thread: Convert a GL texture (GLuint) to QImage or QOpenGLTexture

  1. #1
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    Default Convert a GL texture (GLuint) to QImage or QOpenGLTexture

    Hi,

    I find a lot of way to pass a QImage to GL but in fact i retrieve a gl texture from an API. So i'm trying to convert it either in a QImage or in a QOpenGLTexture to display it. I didn't see any function that could do it. I'm still trying by retrieving the data with glteximage and trying to fill a QImage but i don't know if it will work.

    This is my code to display :
    Qt Code:
    1. void GLWidget::paintGL()
    2. {
    3. glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    4. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    5.  
    6. QMatrix4x4 m;
    7. m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    8. m.translate(0.0f, 0.0f, -10.0f);
    9. nv.StartCapture();
    10. program->setUniformValue("matrix", m);
    11. program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    12. program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    13. program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    14. program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    15. textures[0]->bind();
    16. glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
    17. }
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    If you have any idea.
    Thanks

  2. #2
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    Default Re: Convert a GL texture (GLuint) to QImage or QOpenGLTexture

    There is no direct way to do it since the texture resides in your graphics card's memory. The most direct way I can think of is to render a rectangle with the texture to a frame buffer object and that can easily be converted to a QImage. As for QOpenGLTexture I see nothing in its API that could be used to bind it to an externally defined texture.
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  3. #3
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    Default Re: Convert a GL texture (GLuint) to QImage or QOpenGLTexture

    Hi,
    Thanks for your answer
    Currently, i retrieve the Gltexture from an opengl extension and i was thinking that the best way to draw it was to convert it in QImage. but if i can directly draw it in my glwidget, that's better. I've tried to set the GLTexture in uniform param but i have a black screen for the moment. I'm going to look at the framebuffer.

    Qt Code:
    1. void GLWidget::initializeGL()
    2. {
    3. initializeOpenGLFunctions();
    4. GLenum te=glewInit();
    5. glGenFramebuffers(1, &frameBuffer);
    6. glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    7.  
    8.  
    9. nvc = NVConfig();
    10. nvc.GlobalInit();
    11. nv= NVGL(nvc.l_vioConfig,GetDC((HWND)this->winId()));
    12. makeObject();
    13.  
    14. glEnable(GL_DEPTH_TEST);
    15. glEnable(GL_CULL_FACE);
    16.  
    17. #define PROGRAM_VERTEX_ATTRIBUTE 0
    18. #define PROGRAM_TEXCOORD_ATTRIBUTE 1
    19.  
    20. QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
    21. const char *vsrc =
    22. "attribute highp vec4 vertex;\n"
    23. "attribute mediump vec4 texCoord;\n"
    24. "varying mediump vec4 texc;\n"
    25. "uniform mediump mat4 matrix;\n"
    26. "void main(void)\n"
    27. "{\n"
    28. " gl_Position = matrix * vertex;\n"
    29. " texc = texCoord;\n"
    30. "}\n";
    31. vshader->compileSourceCode(vsrc);
    32.  
    33. QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
    34. const char *fsrc =
    35. "uniform sampler2D texture;\n"
    36. "varying mediump vec4 texc;\n"
    37. "void main(void)\n"
    38. "{\n"
    39. " gl_FragColor = texture2D(texture, texc.st);\n"
    40. "}\n";
    41. fshader->compileSourceCode(fsrc);
    42.  
    43. program = new QOpenGLShaderProgram;
    44. program->addShader(vshader);
    45. program->addShader(fshader);
    46. program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
    47. program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
    48. program->link();
    49. program->bind();
    50. program->setUniformValue("texture", nv.m_videoTexture);
    51. }
    52.  
    53. void GLWidget::paintGL()
    54. {
    55. glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
    56. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    57.  
    58. QMatrix4x4 m;
    59. m.ortho(-1, 1, +1.f, -01.f, 1.0f, 20.0f);
    60. m.translate(0.0f, 0.0f, -10.0f);
    61. nv.StartCapture(); //This function retrieve the GLTexture
    62. program->setUniformValue("matrix", m);
    63. program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
    64. program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
    65. program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
    66. program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));
    67. glDrawArrays(GL_TRIANGLE_FAN, 0 * 4, 4);
    68. }
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    EDIT***
    I still have a black screen, so to be sure i have a correct texture, i saved my texture in .tiff file. And i got a correct result. So my problem is really to draw my texture on the widget
    Last edited by miyoku157; 12th June 2017 at 11:41.

  4. #4
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    Default Re: Convert a GL texture (GLuint) to QImage or QOpenGLTexture

    I finally found my mistake, i was just misbinding my texture. Work great now.

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