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Thread: Cube OpenGL ES 2.0 example with QGraphicsScene

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  1. #1
    Join Date
    Oct 2015
    Posts
    2
    Qt products
    Qt5 Qt/Embedded
    Platforms
    Unix/X11 Windows

    Default Cube OpenGL ES 2.0 example with QGraphicsScene

    Hi,
    I saw https://doc.qt.io/archives/qq/qq26-openglcanvas.html and tried to alter the code of the example "Cube OpenGL ES 2.0" so it uses a QGraphicsView. I only get black screen. I'm on Ubuntu 14.04 / Qt5.3.2.

    main.cpp:
    Qt Code:
    1. #include <QApplication>
    2. #include <QGLWidget>
    3.  
    4. #include "scene.h"
    5. #include "view.h"
    6.  
    7. int main(int argc, char *argv[])
    8. {
    9. QApplication a(argc, argv);
    10. QGLWidget *widget = new QGLWidget(QGLFormat(QGL::SampleBuffers));
    11. widget->setAutoFillBackground(false);
    12. widget->makeCurrent();
    13. Scene *scene= new Scene();
    14. View *mainView = new View();
    15. mainView->setViewport(widget);
    16. mainView->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
    17. mainView->setScene(scene);
    18. mainView->show();
    19. mainView->resize(800,800);
    20. return a.exec();
    21. }
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    scene.cpp:
    Qt Code:
    1. #include "scene.h"
    2.  
    3. #include <QGraphicsScene>
    4. #include <QGraphicsSceneMouseEvent>
    5. #include <QTimer>
    6.  
    7. Scene::Scene() : angularSpeed(0)
    8. {
    9. initializeGLFunctions();
    10. glClearColor(0.0f,0.0f,0.0f,1.0f);
    11. initShaders();
    12. initTextures();
    13. glEnable(GL_DEPTH_TEST);
    14. glEnable(GL_CULL_FACE);
    15. geometries.init();
    16. timer.start(12, this);
    17. }
    18. void Scene::drawBackground(QPainter *painter, const QRectF &rect)
    19. {
    20. painter->beginNativePainting();
    21. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    22. QMatrix4x4 matrix;
    23. matrix.translate(0.0, 0.0, -5.0);
    24. matrix.rotate(rotation);
    25. program.setUniformValue("mvp_matrix", projection * matrix);
    26. program.setUniformValue("texture", 0);
    27. geometries.drawCubeGeometry(&program);
    28. }
    29. void Scene::initShaders()
    30. {
    31. program.addShaderFromSourceFile(QGLShader::Vertex, ":/vshader.glsl");
    32. program.addShaderFromSourceFile(QGLShader::Fragment, ":/fshader.glsl");
    33. program.link();
    34. program.bind();
    35. }
    36. void Scene::initTextures()
    37. {
    38. glEnable(GL_TEXTURE_2D);
    39. textureData = new QOpenGLTexture(QImage(":/cube.png"));
    40. textureData->bind();
    41. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    42. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    43. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    44. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    45. }
    46. void Scene::timerEvent(QTimerEvent *)
    47. {
    48. angularSpeed *= 0.99;
    49. if (angularSpeed < 0.01) {
    50. angularSpeed = 0.0;
    51. } else {
    52. rotation = QQuaternion::fromAxisAndAngle(rotationAxis, angularSpeed) * rotation;
    53. update();
    54. }
    55. }
    56. void Scene::mousePressEvent(QGraphicsSceneMouseEvent *event)
    57. {
    58. mousePressPosition = QVector2D(event->scenePos());
    59. }
    60. void Scene::mouseReleaseEvent(QGraphicsSceneMouseEvent *e)
    61. {
    62. QVector2D diff = QVector2D(e->scenePos()) - mousePressPosition;
    63. QVector3D n = QVector3D(diff.y(), diff.x(), 0.0).normalized();
    64. qreal acc = diff.length() / 100.0;
    65. rotationAxis = (rotationAxis * angularSpeed + n * acc).normalized();
    66. angularSpeed += acc;
    67. }
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    view.h
    Qt Code:
    1. #include <QGraphicsView>
    2. #include <QResizeEvent>
    3. #include "geometryengine.h"
    4.  
    5.  
    6. class View : public QGraphicsView
    7. {
    8. Q_OBJECT
    9. protected:
    10. void resizeEvent(QResizeEvent *event){
    11. if (scene())
    12. scene()->setSceneRect(
    13. QRect(QPoint(0, 0), event->size()));
    14. QGraphicsView::resizeEvent(event);
    15. }
    16. public:
    17. View(){}
    18. };
    19.  
    20. #endif // VIEW_H
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    Any ideas where it went wrong?

  2. #2
    Join Date
    Oct 2015
    Posts
    2
    Qt products
    Qt5 Qt/Embedded
    Platforms
    Unix/X11 Windows

    Default Re: Cube OpenGL ES 2.0 example with QGraphicsScene

    - Projection matrices were missing.
    - Shader bindings must come after beginNativePainting()
    - Buffers must be unbounded in geometryengine.cpp ( glBindBuffer(GL_ARRAY_BUFFER, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);)

    Now program works as intended on ubuntu. When I try it on imx6 Sabre board (3.10.17 with eglfs) I got flicker (like two of the same image try to draw on another (one in smaller resolution, other in fullscreen)). Besides that, dice texture isn't shown (Black cube).

    shader.cpp
    Qt Code:
    1. #include "scene.h"
    2.  
    3. #include <QGraphicsScene>
    4. #include <QGraphicsSceneMouseEvent>
    5. #include <QTimer>
    6. #include <QVBoxLayout>
    7. #include <QLabel>
    8. #include <QGraphicsItem>
    9. #include <QRectF>
    10.  
    11. Scene::Scene() : angularSpeed(0)
    12. {
    13. QWidget *instructions = createDialog(tr("Instructions"));
    14. instructions->layout()->addWidget(new QLabel(tr("Use mouse wheel to zoom model, and click and drag to rotate model")));
    15. instructions->layout()->addWidget(new QLabel(tr("Move the sun around to change the light position")));
    16. addWidget(instructions);
    17.  
    18. QPointF pos(10, 10);
    19. foreach (QGraphicsItem *item, items()) {
    20. item->setFlag(QGraphicsItem::ItemIsMovable);
    21. item->setCacheMode(QGraphicsItem::DeviceCoordinateCache);
    22.  
    23. const QRectF rect = item->boundingRect();
    24. item->setPos(pos.x() - rect.x(), pos.y() - rect.y());
    25. pos += QPointF(0, 10 + rect.height());
    26. }
    27.  
    28. uint32_t w = 800;
    29. uint32_t h = 800;
    30. //glViewport(0, 0, w, h);
    31. qreal aspect = qreal(w) / qreal(h ? h : 1);
    32. const qreal zNear = 1.0, zFar = 7.0, fov = 45.0;
    33. projection.setToIdentity();
    34. projection.perspective(fov, aspect, zNear, zFar);
    35. initShaders();
    36. //initTextures();
    37. textureData = new QOpenGLTexture(QImage(":/cube.png"));
    38. geometries.init();
    39. timer.start(12, this);
    40. }
    41. void Scene::drawBackground(QPainter *painter, const QRectF &rect)
    42. {
    43. painter->beginNativePainting();
    44. glEnable(GL_DEPTH_TEST);
    45. glEnable(GL_CULL_FACE);
    46. glClearColor(0.8f,0.8f,0.1f,1.0f);
    47. program.bind();
    48. textureData->bind();
    49. glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    50. QMatrix4x4 matrix;
    51. matrix.translate(0.0, 0.0, -5.0);
    52. matrix.rotate(rotation);
    53. program.setUniformValue("mvp_matrix", projection * matrix);
    54. program.setUniformValue("texture", 0);
    55. geometries.drawCubeGeometry(&program);
    56. program.release();
    57. textureData->release();
    58. glDisable(GL_DEPTH_TEST);
    59. glDisable(GL_CULL_FACE);
    60. painter->endNativePainting();
    61. QTimer::singleShot(20, this, SLOT(update()));
    62. }
    63. void Scene::initShaders()
    64. {
    65. program.addShaderFromSourceFile(QGLShader::Vertex, ":/vshader.glsl");
    66. program.addShaderFromSourceFile(QGLShader::Fragment, ":/fshader.glsl");
    67. program.link();
    68. // program.bind();
    69. }
    70. void Scene::initTextures()
    71. {
    72. glEnable(GL_TEXTURE_2D);
    73.  
    74. // textureData->bind();
    75. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    76. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    77. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    78. glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    79. }
    80. void Scene::timerEvent(QTimerEvent *)
    81. {
    82. angularSpeed *= 0.99;
    83. if (angularSpeed < 0.01) {
    84. angularSpeed = 0.0;
    85. } else {
    86. rotation = QQuaternion::fromAxisAndAngle(rotationAxis, angularSpeed) * rotation;
    87. update();
    88. }
    89. }
    90. void Scene::mousePressEvent(QGraphicsSceneMouseEvent *event)
    91. {
    92. mousePressPosition = QVector2D(event->scenePos());
    93. }
    94. void Scene::mouseReleaseEvent(QGraphicsSceneMouseEvent *e)
    95. {
    96. QVector2D diff = QVector2D(e->scenePos()) - mousePressPosition;
    97. QVector3D n = QVector3D(diff.y(), diff.x(), 0.0).normalized();
    98. qreal acc = diff.length() / 100.0;
    99. rotationAxis = (rotationAxis * angularSpeed + n * acc).normalized();
    100. angularSpeed += acc;
    101. }
    102.  
    103. QDialog *Scene::createDialog(const QString &windowTitle) const
    104. {
    105. QDialog *dialog = new QDialog(0, Qt::CustomizeWindowHint | Qt::WindowTitleHint);
    106.  
    107. dialog->setWindowOpacity(0.8);
    108. dialog->setWindowTitle(windowTitle);
    109. dialog->setLayout(new QVBoxLayout);
    110.  
    111. return dialog;
    112. }
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    Last edited by jannn; 9th October 2015 at 12:32. Reason: updated contents

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