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Thread: Update QGL Widget on different Thread

  1. #1
    Join Date
    May 2017
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    Qt products
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    Platforms
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    Default Update QGL Widget on different Thread

    Hi,

    Here is my problem, I'm trying to update the QGLWidget from an other thread. But when i try i got this warning:
    "QOpenGLContext::swapBuffers() called without corresponding makeCurrent()"

    I want to retrieve a video stream from a camera and display it on a QGLWidget. With the NVAPI, i fill one image in a GLTexture each frame. That's what i want to display. (and i have displayed it without update it in a thread)
    But as i need to update it continously for the stream, i want to do it in a stream.

    Here is my code:

    Qt Code:
    1. #include "widget.h"
    2. #include "ui_widget.h"
    3.  
    4. Widget::Widget(QGLWidget *parent) :
    5. QGLWidget(parent),
    6. ui(new Ui::Widget)
    7. {
    8. ui->setupUi(this);
    9. }
    10.  
    11. Widget::~Widget()
    12. {
    13.  
    14. nv.cleanupVideo();
    15. th.join();
    16. delete ui;
    17. }
    18.  
    19. void Widget::initializeGL(){
    20. glewInit();
    21. //Initialize the capture of the camera
    22. nv = NVConfig();
    23. this->contextGL = wglGetCurrentContext();
    24. nv.GlobalInit();
    25. nv.LockDevice(GetDC((HWND)this->winId()),this->contextGL);
    26. //Unbind the OpenGL context from this thread.
    27. wglMakeCurrent(0, 0);
    28. //Launch the capture on an other thread
    29. th = std::thread(&Widget::updateGL,this);
    30. }
    31.  
    32. void Widget::resizeGL(int w, int h){
    33. if(h==0)
    34. h =1;
    35. glViewport(0,0,w,h);
    36. glMatrixMode(GL_PROJECTION);
    37. glLoadIdentity();
    38. perspectiveGL(45.0f,w/h,0.1f,100.0f);
    39. glMatrixMode(GL_MODELVIEW);
    40. glLoadIdentity();
    41.  
    42. }
    43.  
    44. /*
    45. * The capture will fill a GL Texture 1280*720; GL_RGBA
    46. *
    47. */
    48. void Widget::updateGL(){
    49. //Start the capture, the previous OpenGL is bind again with
    50. // wglMakeCurrent(GetDC((HWND)this->winId()),this->contextGL)
    51. nv.StartCapture(GetDC((HWND)this->winId()),this->contextGL);
    52. }
    53.  
    54. void Widget::paintGL(){
    55. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    56. glLoadIdentity();
    57. glTranslatef(-1.5f,0.0f,-6.0f);
    58. glBegin(GL_QUADS);
    59. glTexCoord2f(0,1.0f);
    60. glVertex3f(0,0,0);
    61. glTexCoord2f(0,0);
    62. glVertex3f(0,1.0f,0);
    63. glTexCoord2f(1.0f,0);
    64. glVertex3f(1.0f,1.0f,0);
    65. glTexCoord2f(1.0f,1.0f);
    66. glVertex3f(1.0f,0,0);
    67. glEnd();
    68.  
    69.  
    70. }
    71.  
    72. void Widget::perspectiveGL(GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar){
    73. const GLdouble pi = 3.1415926535897932384626433832795;
    74. GLdouble fW, fH;
    75. fH = tan( fovY / 360 * pi) * zNear;
    76. fW = fH * aspect;
    77. glFrustum( -fW,fW,-fH,fH,zNear,zFar);
    78. }
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  2. #2
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    Default Re: Update QGL Widget on different Thread

    You need to make the GL context current to bind it to the thread. When you're done, you can release the context with a corresponding call.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  3. The following user says thank you to wysota for this useful post:

    miyoku157 (9th June 2017)

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