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View Full Version : Drawing rectangle by mouse shows weird shape



michaelpiano
08-17-2016, 06:49 AM
I am using the Qt framework to handle mouse events and other window options.
Also, I'm using OpenGL version 4.5 with nVidia 361.42 in Ubuntu 16.04.
This is my code so far:


void oglCanvas::initializeGL()
{
initializeOpenGLFunctions();

// setting matrices
view.lookAt( // top view
QVector3D(0.0, 0.0, 5.0),
QVector3D(0.0, 0.0, 0.0),
QVector3D(0.0, 1.0, 0.0));
model.setToIdentity();

// background color
glClearColor(0.2, 0.2, 0.2, 1);

initShaders();
initTextures();

// Enable back face culling
glEnable(GL_CULL_FACE);

shapes = new VertexEngine;
}

void oglCanvas::resizeGL(int w, int h)
{
// Calculate aspect ratio
qreal aspect = qreal(w) / qreal(h ? h : 1);

// Set near plane to 3.0, far plane to 7.0, field of view 45 degrees
const qreal zNear = 1.0, zFar = 100.0, fov = 45.0;
// near-z far-z specifies how much your scene is projecting
// it's like the depth your camera can reach [zh-tw: ru/3gp ]
// set near z to 1.0f so mouse coordinates can meet the original size

// Reset projection
projection.setToIdentity();

// Set perspective projection
projection.perspective(fov, aspect, zNear, zFar);
}

void oglCanvas::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

texture->bind();

// send the mvp matrix to GPU
program.setUniformValue("mvp_matrix", projection * view * model);

// use texture unit 0
program.setUniformValue("texture", 0);

// shapes->drawCube(&program);
shapes->draw(&program);
}


void oglCanvas::mousePressEvent(QMouseEvent *event)
{
float thickness = 0.16, zPos = 0; // in model coordinates
QVector3D coord1_0, coord1_1, coord2_0, coord2_1;

if (event->button() == Qt::LeftButton) {
setMouseTracking(true);
coord1 = coord2;
//coord2 = toGLCoord(event->x(), event->y());
coord2.setX(event->x());
coord2.setY((event->y()));
//coord2.setZ(zPos);
if (coord1.x()!=0 && coord1.y()!=0) {
qDebug()<< coord1.x() << coord1.y() <<" : "<< coord2.x()<< coord2.y();
// transform to model coordinate system before passing
coord1.setZ(0.0);
coord1_0 = coord1.unproject(view, projection, this->geometry());
coord2.setZ(0.0);
coord2_0 = coord2.unproject(view, projection, this->geometry());

coord1.setZ(1.0);
coord1_1 = coord1.unproject(view, projection, this->geometry());
coord2.setZ(1.0);
coord2_1 = coord2.unproject(view, projection, this->geometry());

coord1 = coord1_0 + 5/(100.0-0.1)*(coord1_1 - coord1_0);
coord2 = coord2_0 + 5/(100.0-0.1)*(coord2_1 - coord2_0);

qDebug()<< coord1.x() << coord1.y() << coord1.z() <<" : "<< coord2.x()<< coord2.y() << coord2.z();
shapes->addRect(coord1, coord2, zPos, zPos + thickness);
coord2 = QVector3D(0,0,0);
setMouseTracking(false);
}
}
}



void VertexEngine::addRect(QVector3D p1, QVector3D p3, float zstart, float zstop)
{
QVector3D center = (p1 + p3)/2;
QVector3D p2 = QVector3D(p3.x(), p1.y(), 0);
QVector3D p4 = QVector3D(p1.x(), p3.y(), 0);
center.setZ(zstart);
p1.setZ(zstart);
p2.setZ(zstart);
p3.setZ(zstart);
p4.setZ(zstart);
TexturedVertex temp_vertex[] = {
{p1, QVector2D(0.0f, 1.0f)},
{p2, QVector2D(0.0f, 0.0f)},
{p3, QVector2D(1.0f, 0.0f)},
{p4, QVector2D(1.0f, 1.0f)}
};
GLushort ind[4] = {
0, 1, 2, 3
};

std::copy(temp_vertex,temp_vertex+3,vertex);
std::copy(ind,ind+4,index);

updateBuffer();
qDebug()<< "rectangle created";
}

void VertexEngine::draw(QOpenGLShaderProgram *program)
{
arrBuf.bind();
indBuf.bind();

qintptr offset = 0;

program->enableAttributeArray(0); // a_position
program->setAttributeBuffer(0, GL_FLOAT, offset, 3, sizeof(TexturedVertex));

offset += sizeof(QVector3D);

program->enableAttributeArray(1); // a_texcoord
program->setAttributeBuffer(1, GL_FLOAT, offset, 2, sizeof(TexturedVertex));

GLsizei count[] = {sizeof(vertex)};
GLvoid* index_test[] = {
BUFFER_OFFSET(0)
};

//! crashed because of some weird pointer issue
//glMultiDrawElements( GL_POLYGON, count, GL_UNSIGNED_SHORT, index_test, sizeof(count) );
glDrawElements(GL_POLYGON, sizeof(index), GL_UNSIGNED_SHORT, 0);
//qDebug()<< "elements drawed";

/*for (int i = 0; i < primcount; ++i) {
glDrawElements(GL_TRIANGLE_FAN, count[i], GL_UNSIGNED_SHORT, index[i]);
}*/
}

void VertexEngine::updateBuffer()
{
arrBuf.bind();
arrBuf.allocate(&vertex, sizeof(vertex) * sizeof(TexturedVertex));
indBuf.bind();
indBuf.allocate(&index, sizeof(index) * sizeof(GLushort));
qDebug()<< "buffer set!";
}


As you can see above, I constructed my rectangle using a polygon in CCW order, but most of the times the shapes didn't end up at my cursor :doh:
The editor keep giving me an error "not a valid image file" so I can't post images right now.
can someone tell me what might be the cause?