Question

In OpenGL, I draw tree(composed of lines) like structure(neurons), and based on activity, i apply a color on each of the branches of the tree. Each branch portion may have a different color at an instance. I keep record of the color at an instance corresponding to the branch.

I am able to rotate (by changing the modelview matrix) the tree. I can see the changing color (activity) on the branches when updating.

However, i am not able to rotate the tree while the color change is happening. (the rotation is seen after the complete updating) This is also true with translating the model, not able to translate while updating.

How should i be doing this to see them simultaneously?

i call the updateViz function to update the colors.

def render(self):
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()
    self.renderAxis()   #draws 3 axes at origin
    for obj in self.vizObjects:
        glPushMatrix()
        glColor(obj.r, obj.g, obj.b)
        glLineWidth(2)
        glBegin(GL_LINES)
        glVertex3f(obj.l_coords[0],obj.l_coords[1],obj.l_coords[2])
        glVertex3f(obj.l_coords[3],obj.l_coords[4],obj.l_coords[5])
        glEnd()     
        glPopMatrix()

def updateViz(self,vals):
    inds = digitize(vals,colrMapVals)
    for i in range(0,len(self.vizObjects)):
        self.vizObjects[i].r,self.vizObjects[i].g,self.vizObjects[i].b= colorMap[inds[i]-1]

def translate(self, _trans):
    self.makeCurrent()
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()
    glTranslated(_trans[0], _trans[1], _trans[2])
    glMultMatrixd(self.modelview_matrix_)
    self.modelview_matrix_ = glGetDoublev(GL_MODELVIEW_MATRIX)
    self.translate_vector_[0] = self.modelview_matrix_[3][0]
    self.translate_vector_[1] = self.modelview_matrix_[3][1]
    self.translate_vector_[2] = self.modelview_matrix_[3][2]

def rotate(self, _axis, _angle):
    #self.modelview_matrix_ = glGetDoublev(GL_MODELVIEW_MATRIX)
    t = [self.modelview_matrix_[0][0] * self.center_[0] +
         self.modelview_matrix_[1][0] * self.center_[1] +
         self.modelview_matrix_[2][0] * self.center_[2] +
         self.modelview_matrix_[3][0],
         self.modelview_matrix_[0][1] * self.center_[0] +
         self.modelview_matrix_[1][1] * self.center_[1] +
         self.modelview_matrix_[2][1] * self.center_[2] +
         self.modelview_matrix_[3][1],
         self.modelview_matrix_[0][2] * self.center_[0] +
         self.modelview_matrix_[1][2] * self.center_[1] +
         self.modelview_matrix_[2][2] * self.center_[2] +
         self.modelview_matrix_[3][2]]

    self.makeCurrent()
    glLoadIdentity()
    glTranslatef(t[0], t[1], t[2])
    glRotated(_angle, _axis[0], _axis[1], _axis[2])
    glTranslatef(-t[0], -t[1], -t[2])
    glMultMatrixd(self.modelview_matrix_)
    self.modelview_matrix_ = glGetDoublev(GL_MODELVIEW_MATRIX)

def keyPressEvent(self, ev):
    if (ev.key() == QtCore.Qt.Key_Left):
        self.translate([-0.25, 0.0, 0.0])
        self.updateGL()
    elif (ev.key() == QtCore.Qt.Key_Right):
        self.translate([0.25, 0.0, 0.0])
        self.updateGL()
    elif (ev.key() == QtCore.Qt.Key_A):
        self.rotate([1.0, 0.0, 0.0],2.0)
        self.updateGL()
    elif (ev.key() == QtCore.Qt.Key_Q):
        self.rotate([1.0, 0.0, 0.0],-2.0)
        self.updateGL()

I use PyQt4 and PyGLWidget

Answer 1

your code looks all right to me. I think the problem is caused by how you update the rotation and color. OpenGL is a state machine, you feed it with all kinds of info (vertex pos, color, etc) and things get rendered, so MAKE SURE updateVis and translate/rotate are called on EVERY FRAME.

maybe your rotation/translation depends on Qt’s signal/event mechanism, and it’s not called every frame?