I recently needed to implement a function in the QT+OPENGL environment, that is, I drew a cube (presumably in the center of the view) in my own defined framebuffer (I defined it as fbo) and colored it in red. And nothing is drawn in the default buffer, so I can't see my cube in the view (but it is drawn in the framebuffer fbo)
I hope that when I click in the middle of the view (the position of the cube), I can display the color of the cube----red instead of the color of the background of the view.
Here are the problems I have encountered: I can only get the color of the background of the view with the mouse, and the cube drawn in the frame buffer is not picked up (the cube is red).
In the initializeGL() function, I initialized and configured the framebuffer fbo and some of the configuration required to draw the cube.
In the paintGL() function, I bind my defined framebuffer to GL_FRAMEBUFFER and then do the drawing.
In the mousePressEvent(QMouseEvent *e) function, I did the picking work. This is the response function of the QT mouse click. I put the information read by glReadPixels into the array pix and print it out.
void OpenglWidget::initializeGL()
{
core1 = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_4_0_Core>();
core = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_3_3_Core>();
core->glGenFramebuffers(1, &fbo);
core->glBindFramebuffer(GL_FRAMEBUFFER, fbo);
// Create the texture object for the primitive information buffer
core->glGenTextures(1, &m_pickingTexture);
glBindTexture(GL_TEXTURE_2D, m_pickingTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB32UI, SCR_WIDTH, SCR_HEIGHT,
0, GL_RGB_INTEGER, GL_UNSIGNED_INT, NULL);
core1->glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D,
m_pickingTexture, 0);
// Create the texture object for the depth buffer
core->glGenTextures(1, &m_depthTexture);
core->glBindTexture(GL_TEXTURE_2D, m_depthTexture);
core->glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT,
0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
core1->glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D,
m_depthTexture, 0);
// Disable reading to avoid problems with older GPUs
core->glReadBuffer(GL_NONE);
// Verify that the FBO is correct
GLenum Status = core->glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (Status == GL_FRAMEBUFFER_COMPLETE) {
qDebug() << "ok";
}
// Restore the default framebuffer
core->glBindTexture(GL_TEXTURE_2D, 0);
core->glBindFramebuffer(GL_FRAMEBUFFER, 0);
GLfloat verticPosition[] = {
-0.5f, -0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
0.5f, 0.5f, -0.5f,
0.5f, 0.5f, -0.5f,
-0.5f, 0.5f, -0.5f,
-0.5f, -0.5f, -0.5f,
-0.5f, -0.5f, 0.5f,
0.5f, -0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f, -0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, -0.5f,
-0.5f, -0.5f, -0.5f,
-0.5f, -0.5f, -0.5f,
-0.5f, -0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
0.5f, 0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
0.5f, -0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
-0.5f, -0.5f, -0.5f,
0.5f, -0.5f, -0.5f,
0.5f, -0.5f, 0.5f,
0.5f, -0.5f, 0.5f,
-0.5f, -0.5f, 0.5f,
-0.5f, -0.5f, -0.5f,
-0.5f, 0.5f, -0.5f,
0.5f, 0.5f, -0.5f,
0.5f, 0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, -0.5f,
};
GLint beamIndices[] = {
0,1,2,3,4,5,6,7
};
core->glGenVertexArrays(1, &VAOBeam);
core->glGenBuffers(1, &VBOBeam);
core->glGenBuffers(1, &EBOBeam);
core->glBindVertexArray(VAOBeam);
core->glBindBuffer(GL_ARRAY_BUFFER, VBOBeam);
core->glBufferData(GL_ARRAY_BUFFER,sizeof(float) * 3 * 36, verticPosition, GL_STATIC_DRAW);
core->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBOBeam);
core->glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLint) * 8, beamIndices, GL_STATIC_DRAW);
core->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
core->glEnableVertexAttribArray(0);
core->glBindBuffer(GL_ARRAY_BUFFER, 0);
core->glBindVertexArray(0);
}
void OpenglWidget::paintGL()
{
core->glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glClearColor(0,0,1,1);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
float frametime =GetFrameTime();
mCamera.Update(frametime);
Shader GLprogram = Shader("E:\\QT\\OpenglTest\\vs.vert","E:\\QT\\OpenglTest\\fs.frag");
GLprogram.use();
core->glBindVertexArray(VAOBeam);
glm::mat4 model = glm::mat4(1.0f);
model = glm::translate(model, mCamera.TempTranslateVrc);
glm::mat4 view = glm::mat4(1.0f);
//view = glm::lookAt(glm::vec3(0.0f, 0.0f, 1.0f), glm::vec3(0.5f,0.5f,0.0f), glm::vec3(0.0f, 1.0f, 0.0f));
view = glm::lookAt(mCamera.mPos,mCamera.mViewCenter,mCamera.mUp);
glm::mat4 projection = glm::mat4(1.0f);
projection = glm::perspective(glm::radians(45.0f), (float)1.0, 0.1f, 100.0f);
GLprogram.setMatrix4f("model",model);
GLprogram.setMatrix4f("view",view);
GLprogram.setMatrix4f("projection",projection);
core->glDrawArrays(GL_TRIANGLES,0,36);
core->glUseProgram(0);
update();
}
void OpenglWidget::mousePressEvent(QMouseEvent *e)
{
core1 = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_4_0_Core>();
float pix[4] = {0.0};
mCamera.getInitPos(e->x(),e->y());//This is the camera's setup function, no need to worry about it.
core1->glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
core1->glReadBuffer(GL_COLOR_ATTACHMENT1);
core1->glReadPixels(e->x() , 500 - e->y() + 65, 1, 1, GL_RGBA, GL_FLOAT, pix);
qDebug() << e->x()<< 500 - e->y() <<pix[0] << pix[1] << pix[2] << pix[3];
}
I can only get the color of the background of the view with the mouse, and the cube drawn in the frame buffer is not picked up (the cube is red).
