Qt5.7 QVector3D::unproject() mouse picking
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Hi !
I would like to "select" an object in my OpenGL world but first of all, I need to find the mouse position in the OpengGL world coordinates and I thought that the QVector3D::unproject() function was the best but I'm not getting what I want : the world coordinates I get don't seem to be right as I created a triangle, one of his corner is (-0.5, -0.5, 0.0) and when I click with the mouse on it, I get (1.96532, -3.93444, 4.93216).
I tried to change the z coordinate, move the camera ... but I never get close to a working code.
This is a part of my code so far :QMatrix4x4 modelView; modelView.setToIdentity(); modelView.lookAt(m_camera.getPosition(), m_camera.getTarget(), m_camera.getUp()); QMatrix4x4 projection; projection.perspective(70.0, width() / height(), 0.1, 120.0); GLint view[4]; glGetIntegerv(GL_VIEWPORT, &view[0]); QVector3D worldPosition = QVector3D(event->pos().x(), event->pos().y(), 0).unproject(modelView, projection, QRect(view[0], view[1], view[2], view[3])); qDebug() << worldPosition;I don't understand what's going wrong. Do you have a clue ?
Thanks in advance -
Try and edit following function from my old project: https://github.com/glararan/QEditor/blob/master/src/mapview.cpp#L1175
I guess based on your description, this is what you're looking for.
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Thank you for the help, I copy / pasted your code just to try it but I get values from (1.9, -3.8, 4.9) at the top left-hand corner of the window to (2.0, -3.9, 4.8) at the bottom right-hand corner of the window.
There is your code with my modifications. Do you see what I'm doing wrong ?QMatrix4x4 viewMatrix ; viewMatrix.lookAt(m_camera.getPosition(), m_camera.getTarget(), m_camera.getUp()); QMatrix4x4 projection; projection.perspective(70.0, width() / height(), 0.1, 120.0); QMatrix4x4 viewportMatrix; float w2 = width() / 2.0f; float h2 = height() / 2.0f; viewportMatrix.setToIdentity(); viewportMatrix.setColumn(0, QVector4D(w2, 0.0f, 0.0f, 0.0f)); viewportMatrix.setColumn(1, QVector4D(0.0f, h2, 0.0f, 0.0f)); viewportMatrix.setColumn(2, QVector4D(0.0f, 0.0f, 1.0f, 0.0f)); viewportMatrix.setColumn(3, QVector4D(w2, h2, 0.0f, 1.0f)); QMatrix4x4 modelMatrix; modelMatrix.setToIdentity(); QMatrix4x4 modelViewMatrix = viewMatrix * modelMatrix; QMatrix4x4 modelViewProject = projection * modelViewMatrix; QMatrix4x4 inverted = viewportMatrix * modelViewProject; inverted = inverted.inverted(); float posZ; float posY = height() - y - 1.0f; glReadPixels((int)x, (int)posY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &posZ); QVector4D clickedPointOnScreen(x, posY, 2.0f * posZ - 1.0f, 1.0f); QVector4D clickedPointIn3DOrgn = inverted * clickedPointOnScreen; clickedPointIn3DOrgn /= clickedPointIn3DOrgn.w(); qDebug() << clickedPointIn3DOrgn.toVector3DAffine(); -
I did some experimental researches and I finally discovered the problem, it was the z coordinate.
I've found the experimental value (0.961635) but I need the law to make the code work if I move the camera.
This is a new project that I made to see things more clearly :#include "mainwindow.h" #include <QVector3D> #include <QKeyEvent> #include <qDebug> MainWindow::MainWindow(QWidget *parent) : QOpenGLWidget(parent) { } MainWindow::~MainWindow() { } void MainWindow::initializeGL() { initializeOpenGLFunctions(); glClearColor(0.7f, 0.7f, 1.0f, 0.0f); m_program.addShaderFromSourceFile(QOpenGLShader::Vertex, ":/vertexshader.vsh"); m_program.addShaderFromSourceFile(QOpenGLShader::Fragment, ":/fragmentshader.fsh"); m_program.link(); m_matrix.setToIdentity(); m_matrix.perspective(70.0, width() / height(), 0.1, 120.0); m_matrix.lookAt(QVector3D(0, 0, 5), QVector3D(0, 0, 0), QVector3D(0, 1, 0)); } void MainWindow::paintGL() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); m_program.bind(); m_program.setUniformValue("mvp", m_matrix); GLfloat vertices[] = { 0.0f, 1.0f, 0.0f, -0.5f, -0.5f, 0.0f, 0.5f, -0.5f, 0.0f }; glVertexAttribPointer(m_program.attributeLocation("vertexPosition_modelspace"), 3, GL_FLOAT, GL_FALSE, 0, vertices); glEnableVertexAttribArray(0); glDrawArrays(GL_TRIANGLES, 0, 3); glDisableVertexAttribArray(0); m_program.release(); } void MainWindow::mousePressEvent(QMouseEvent *event) { QMatrix4x4 viewMatrix ; viewMatrix.setToIdentity(); viewMatrix.lookAt(QVector3D(0, 0, 5), QVector3D(0, 0, 0), QVector3D(0, 1, 0)); QMatrix4x4 projection; projection.setToIdentity(); projection.perspective(70.0, width() / height(), 0.1, 120.0); QMatrix4x4 viewportMatrix; float w2 = width() / 2.0f; float h2 = height() / 2.0f; viewportMatrix.setToIdentity(); viewportMatrix.setColumn(0, QVector4D(w2, 0.0f, 0.0f, 0.0f)); viewportMatrix.setColumn(1, QVector4D(0.0f, h2, 0.0f, 0.0f)); viewportMatrix.setColumn(2, QVector4D(0.0f, 0.0f, 1.0f, 0.0f)); viewportMatrix.setColumn(3, QVector4D(w2, h2, 0.0f, 1.0f)); QMatrix4x4 modelMatrix; modelMatrix.setToIdentity(); QMatrix4x4 modelViewMatrix = viewMatrix * modelMatrix; QMatrix4x4 modelViewProject = projection * modelViewMatrix; QMatrix4x4 inverted = viewportMatrix * modelViewProject; inverted = inverted.inverted(); float posZ; float posY = height() - event->pos().y() - 1.0f; glReadPixels((int)event->pos().x(), (int)posY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &posZ); qDebug() << 2.0f * posZ - 1.0f; QVector4D clickedPointOnScreen(event->pos().x(), posY, 0.961635, 1.0f); QVector4D clickedPointIn3DOrgn = inverted * clickedPointOnScreen; clickedPointIn3DOrgn /= clickedPointIn3DOrgn.w(); qDebug() << clickedPointIn3DOrgn.toVector3DAffine(); } -
After some testing, it turned out that I need the projected z coordinate to unproject the x and y but in order to get it, I need the unprojected x and y ... it's an infinite loop !
Here's the code I came up with :QMatrix4x4 viewMatrix ; viewMatrix.lookAt(m_camera.getPosition(), m_camera.getTarget(), m_camera.getUp()); QMatrix4x4 projection; projection.perspective(70.0, width() / height(), 0.1, 120.0); QVector3D Z(0, 0, 0); // instead of 0 for x and y i need worldPosition.x() and worldPosition.y() .... Z = Z.project(viewMatrix, projection, QRect(0, 0, width(), height())); QVector3D worldPosition = QVector3D(x, height() - y, Z.z()).unproject(viewMatrix, projection, QRect(0, 0, width(), height())); qDebug() << worldPosition; -
I was searching for a way the pass few days. This reference is the most detailed I have seen.
Long story short, screen coordinates (x, y, 0) will transfer into the near field z value, and (x, y, 1) will transfer into far field z value. If you want the values in between a specific position, linear interpolation will help.
