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Qt5 - QOpenGL terrain, trying get terrain coords by mouse


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#1 glararan   Members   -  Reputation: 215

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Posted 06 August 2013 - 12:43 PM

Hello,

I looking for something what will return xyz position on my terrain.

I used gluUnProject, but it still returning “nan” values

gluUnProject:

  1. GLint viewport[4];
  2.         GLdouble modelview[16], projection[16], posX, posY, posZ;
  3.         GLfloat winX, winY, winZ;
  4.  
  5.        // m_funcs = QOpenGLFunctions_4_1_Core
  6.        m_funcs->glGetIntegerv(GL_VIEWPORT, viewport);
  7.        m_funcs->glGetDoublev(GL_MODELVIEW_MATRIX, modelview);
  8.        m_funcs->glGetDoublev(GL_PROJECTION_MATRIX, projection);
  9.  
  10.         winX = mouse_position.x();
  11.         winY = static_cast<float>(viewport[3]) - mouse_position.y();
  12.  
  13.         m_funcs->glReadPixels(winX, winY, 1, 1, GL_DEPTH_COMPONENT,GL_FLOAT, &winZ);
  14.         gluUnProject(winX, winY, winZ, modelview, projection, viewport, &posX,&posY, &posZ);
  15.  
  16.         terrain_pos = QVector3D(posX, posY, posZ);

 

gluUnProject v2:

  1. GLint viewport[4];
  2.         GLdouble modelview[16], projection[16], posX, posY, posZ;
  3.         GLfloat winX, winY, winZ;
  4.  
  5.         int indexing = 0;
  6.  
  7.         // passing from own Camera class QMatrix4x4 modelView, projection and viewport
  8.         for(int i = 0; i < 4; i++)
  9.         {
  10.             viewport[i] = viewMatrix(0, i);
  11.  
  12.             for(int j = 0; j < 4; j++)
  13.             {
  14.                 modelview[indexing] = modelViewMatrix(i, j);
  15.                 projection[indexing] = mvp(i, j);
  16.  
  17.                 indexing++;
  18.             }
  19.         }
  20.  
  21.         winX = mouse_position.x();
  22.         winY = /*static_cast<float>(viewport[3]) -*/ mouse_position.y();
  23.  
  24.         m_funcs->glReadPixels(winX, winY, 1, 1, GL_DEPTH_COMPONENT,GL_FLOAT, &winZ);
  25.         gluUnProject(winX, winY, winZ, modelview, projection, viewport, &posX,&posY, &posZ);
  26.  
  27.         terrain_pos = QVector3D(posX, posY, posZ);

 

Every array and params have values in gluUnProject v2, so I don’t know why it returns nan :(

Then I tried to use some code from google, but it returns out range positions

  1. QMatrix4x4 mProjection = m_camera->viewMatrix() * m_camera->projectionMatrix();
  2.         QMatrix4x4 mInverse = mProjection.inverted();
  3.  
  4.         float in[4];
  5.         float winZ = 1.0f;
  6.  
  7.         in[0] = (2.0f * ((float)(mouse_position.x() - 0) / (this->width() - 0))) - 1.0f,
  8.         in[1] = 1.0f - (2.0f * ((float)(mouse_position.y() - 0) / (this->height() - 0)));
  9.         in[2] = 2.0f * winZ - 1.0f;
  10.         in[3] = 1.0f;
  11.  
  12.         QVector4D vIn(in[0], in[1], in[2], in[3]);
  13.  
  14.         QVector4D Vpos = vIn * mInverse;
  15.  
  16.         Vpos.setW(1.0f / Vpos.w());
  17.         Vpos.setX(Vpos.x() * Vpos.w());
  18.         Vpos.setY(Vpos.y() * Vpos.w());
  19.         Vpos.setZ(Vpos.z() * Vpos.z());
  20.  
  21.         terrain_pos = QVector3D(Vpos.x(), Vpos.y(), Vpos.z());

Is any better way to get heightmap xyz in Qt? Or its possible with Qt OpenGL and not with basic GL? Or why it doesnt work?

Using QGLWidget with QOpenGL headers and GL version 4.1

 

Pic from app: (I have debug mode, so I see QVector3D posX, posY, posZ returning nan)

34df6076f7cd758f8ba10f6ca928e875.png

 



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#2 glararan   Members   -  Reputation: 215

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Posted 09 August 2013 - 06:57 AM

BUMP

 

I’m trying to get terrain coords from camera QMatrix4×4, but it returns incorrets values.

Im using in camera these properties:
viewMatrix, projectionMatrix and viewProjectionMatrix.

I tried to figure it out with this code:

  1.         QMatrix4x4 inverted = m_camera->projectionMatrix() * m_camera->viewMatrix();
  2.         inverted = inverted.inverted();
  3.  
  4.         float posZ;
  5.  
  6.         // m_funcs = QOpenGLFuncions_4_0_Core
  7.         m_funcs->glReadPixels(mouse_position.x(), mouse_position.y(), 1, 1,GL_DEPTH_COMPONENT, GL_FLOAT, &posZ);
  8.  
  9.         QVector4D clickedPointOnScreen(mouse_position.x(),mouse_position.y(), posZ, 1.0f);
  10.         QVector4D clickedPointIn3DOrgn = inverted * clickedPointOnScreen;
  11.  
  12.         terrain_pos = clickedPointIn3DOrgn.toVector3D();
  13.  
  14.         qDebug()  << terrain_pos;

 

I’m with camera on position: 250.0f, 10.0f, 250.0f
And I’m getting: QVector3D(415.715, 99.3959, 6.45992) (cursor is in center ofQGLWidget screen, i calculated coords). It should be QVector3D(250.0f, 10.0f, 260f+-)






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