How to change vertices in QOpenGLWidget dynamically? - c++

Question

I use QOpenGLWidget to derive my own widget rendered OpenGL. I want to set vertices data later or changed them whenever possible instead of in initializeGL(). Trying to draw a triangle by giving vertices in initializedGL() is ok. But I want to call updateModel() function externally to changed model whenever I want.
In initializeGL(), commented lines are standard use of QOpenGLWidget. It works well. When I call updateModel() to changed vertices, it can't draw anything.
What's wrong? Thanks.
#include "openglwindow.h"
#include <QDebug>
#include <QOpenGLShader>
#include <QOpenGLShaderProgram>
#include <QDebug>
#include <QMouseEvent>
#include <QWheelEvent>
#include <QVector3D>
#include <QTimer>
OpenGLWidget::OpenGLWidget(QWidget *parent):
QOpenGLWidget(parent),
m_vshader(0),
m_fshader(0),
m_program(0),
m_mousePressed(false),
m_eye(QVector3D(0,0,10)),
m_center(QVector3D(0,0,0)),
m_up(QVector3D(0,1,0)),
m_verticalAngle(45.f){
m_modelUpdated = false;
setMinimumSize(300,300);
//matrix initialization
m_model.setToIdentity();
m_view.lookAt(m_eye,m_center,m_up),
m_projection.perspective(m_verticalAngle,aspectRatio(),0.01f,100.0f);
m_timer = new QTimer(this);
m_timer->setInterval(10);
connect(m_timer,&QTimer::timeout,this,QOverload<>::of(&QWidget::update));
}
OpenGLWidget::~OpenGLWidget()
{
// makeCurrent();
// delete m_program;
// delete m_vshader;
// delete m_fshader;
// m_vbo.destroy();
// m_vao.destroy();
// doneCurrent();
}
void OpenGLWidget::initializeGL()
{
qDebug()<<"initializeGL()";
initializeOpenGLFunctions();
glEnable(GL_DEPTH_TEST);
glClearColor(.2f,.3f,.3f,1.0f);
//Initialized program shader
m_vshader = new QOpenGLShader(QOpenGLShader::Vertex);
const char * vcode =
"#version 330 core \
layout (location = 0) in vec3 aPos;\
layout (location = 1) in vec3 aNor; \
uniform mat4 model; \
uniform mat4 view; \
uniform mat4 projection;\
out vec3 Normal;\
out vec3 FragPos;\
void main() \
{ \
gl_Position = projection*view*model*vec4(aPos,1.0);\
Normal = aNor;\
FragPos = vec3(model*vec4(aPos,1.0));\
}";
m_vshader->compileSourceCode(vcode);
m_fshader = new QOpenGLShader(QOpenGLShader::Fragment);
const char * fcode =
"#version 330 core \
out vec4 FragColor; \
in vec3 Normal;\
in vec3 FragPos;\
void main()\
{ \
FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\
} ";
m_fshader->compileSourceCode(fcode);
m_program = new QOpenGLShaderProgram();
m_program->addShader(m_vshader);
m_program->addShader(m_fshader);
m_program->link();
m_program->bind();
m_attriPos = m_program->attributeLocation("aPos");
// m_modelAttriLocation = m_program->attributeLocation("model");
// m_viewAttriLocation = m_program->attributeLocation("view");
// m_projectAttriLocation = m_program->attributeLocation("projection");
// m_vertices<<QVector3D(-0.5f,-0.5f,0.0f)
// <<QVector3D(0.5f,-0.5f,0.0f)
// <<QVector3D(0.0f,0.5f,0.0f)
// <<QVector3D(-0.5f,0.5f,0.0f)
// <<QVector3D(0.5f,0.5f,0.0f)
// <<QVector3D(0.0f,-0.5f,0.0f);
//create VAO
m_vao.create();
m_vao.bind();
//create VBO
m_vbo.create();
qDebug()<<m_vbo.bind();
m_vbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
m_vbo.allocate(m_vertices.constData(),m_vertices.count()*3*sizeof(float));
m_program->enableAttributeArray(0);
m_program->setAttributeBuffer(0,GL_FLOAT,0,3);
//m_vbo.release();
//m_vao.release();
m_program->release();
}
void OpenGLWidget::resizeGL(int w, int h){
//Updating m_projection matrix here
m_projection.setToIdentity();
m_projection.perspective(45.0f,w/float(h),0.01f,100.0f);
}
void OpenGLWidget::paintGL(){
//glClearColor(.2f,.3f,.3f,1.0f);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
// m_program->bind();
// {
// m_program->setUniformValue("projection",m_projection);
// m_program->setUniformValue("view",m_view);
// m_program->setUniformValue("model",m_model);
// m_vao.bind();
// glDrawArrays(GL_TRIANGLES,0,3);
// m_vao.release();
// }
// m_program->release();
paintModel();
}
void OpenGLWidget::mousePressEvent(QMouseEvent *event)
{
m_mousePressed = true;
m_prevXPos = event->x();
m_prevYPos = event->y();
}
void OpenGLWidget::mouseMoveEvent(QMouseEvent *event)
{
if(m_mousePressed == true){
//update matrix here
int deltaX = event->x()-m_prevXPos;
int deltaY = event->y()-m_prevXPos;
updateCameraVectors(deltaX,deltaY);
}
}
void OpenGLWidget::mouseReleaseEvent(QMouseEvent *event)
{
m_mousePressed = false;
}
void OpenGLWidget::wheelEvent(QWheelEvent *event)
{
updateCameraVectors(0,0,event->angleDelta().y());
}
float OpenGLWidget::aspectRatio()
{
return width()/static_cast<float>(height());
}
void OpenGLWidget::paintModel()
{
m_program->bind();
{
m_vao.bind();
m_program->setUniformValue("projection",m_projection);
m_program->setUniformValue("view",m_view);
m_program->setUniformValue("model",m_model);
glDrawArrays(GL_TRIANGLES,0,m_vertices.count());
m_vao.release();
}
m_program->release();
}
void OpenGLWidget::updateModel(const QVector<QVector3D> &model)
{
m_vertices = model;
if(isValid() == false)
return;
makeCurrent();
m_vbo.destroy();
m_vao.destroy();
if(m_vbo.isCreated() == false){
m_vao.create();
m_vao.bind();
m_vbo.create();
m_vbo.bind();
m_vbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
m_vbo.allocate(m_vertices.constData(),m_vertices.count()*3*sizeof(float));
for(GLenum err;(err = glGetError())!=GL_NO_ERROR;){
qDebug()<<"error:"<<err;
}
m_vbo.release();
m_vao.release();
}
doneCurrent();
}

Answer 1

When the VBO/VAO get deleted and recreated, you also have to redo the VAO setup, namely
m_program->enableAttributeArray(0);
m_program->setAttributeBuffer(0,GL_FLOAT,0,3);
You might be confused because these functions are called on the shader program object, but they are actually part of the VAO state.
Note, that deleting and generating the VAO/VBO again in the updateModel is not really necessary. If you want to change the vertices, it is sufficient to call m_vbo.allocate with the new data.