openGL (Qt) bind properly + Two rotation at the same time - qt

Question

I'm trying to get some experience in openGL, but now I'm facing "1.5" problems ;).
The first problem / question is how can I get a rotation in two directions "simultaneously"?
I want to draw a coordinate system which is movable on the x- and y-axis. But I'm only able to move on the x-axis or y-axis. I can't figure it out how to do both at the same time.
My other half problem is not really a problem but as you can see I'm binding my shaders all the time new when I move my mouse. Is there a better way how it could been done?
void GLWidget::mouseMoveEvent(QMouseEvent *event)
{
differencePostition.setX(event->x() - lastPosition.x());
differencePostition.setY(event->y() - lastPosition.y());
shaderProgram.removeAllShaders();
shaderProgram.addShaderFromSourceFile(QGLShader::Vertex, "../Vector/yRotation.vert");
shaderProgram.addShaderFromSourceFile(QGLShader::Fragment, "../Vector/CoordinateSystemLines.frag");
shaderProgram.link();
shaderProgram.bind();
shaderProgram.setAttributeValue("angle", differencePostition.x());
//shaderProgram.release();
//shaderProgram.addShaderFromSourceFile(QGLShader::Vertex, "../Vector/xRotation.vert");
//shaderProgram.addShaderFromSourceFile(QGLShader::Fragment, "../Vector/CoordinateSystemLines.frag");
//shaderProgram.link();
//shaderProgram.bind();
//shaderProgram.setAttributeValue("angle", differencePostition.y());
updateGL();
}
void GLWidget::mousePressEvent(QMouseEvent *event)
{
lastPosition = event->posF();
}
xRotation.vert
#version 330
in float angle;
const float PI = 3.14159265358979323846264;
void main(void)
{
float rad_angle = angle * PI / 180.0;
vec4 oldPosition = gl_Vertex;
vec4 newPosition = oldPosition;
newPosition.y = oldPosition.y * cos(rad_angle) - oldPosition.z * sin(rad_angle);
newPosition.z = oldPosition.y * sin(rad_angle) + oldPosition.z * cos(rad_angle);
gl_Position = gl_ModelViewProjectionMatrix * newPosition;
}
yRotation.vert
#version 330
in float angle;
const float PI = 3.14159265358979323846264;
void main(void)
{
float rad_angle = angle * PI / 180.0;
vec4 oldPosition = gl_Vertex;
vec4 newPosition = oldPosition;
newPosition.x = oldPosition.x * cos(rad_angle) + oldPosition.z * sin(rad_angle);
newPosition.z = oldPosition.z * cos(rad_angle) - oldPosition.x * sin(rad_angle);
gl_Position = gl_ModelViewProjectionMatrix * newPosition;
}

Answer 1

Rotation in more than one direction at the same time requires a combination of matrices ( commonly called a general rotation matrix )
There are several sites that show how this matrix is generated if you are more interested.
As to your second problem, the shaders are usually initialized in the init section.
Example: http://doc-snapshot.qt-project.org/5.0/qtopengl/cube-mainwidget-cpp.html

Answer 2

You only need to call shaderProgram.bind(); every time before you want to draw an object with your shader. Loading and linking is usually only done once in the initialization of your programm. Only call shaderProgram.setAttributeValue your mouseMoveEvent method.
EDIT
A quick way to solve your rotation problem is to write a shader that does both rotations one after the other. Add a second in variable and set both using the setAttributeValue method.
#version 330
in float angleX;
in float angleY;
const float PI = 3.14159265358979323846264;
void main(void)
{
float rad_angle_x = angleX * PI / 180.0;
vec4 oldPosition = gl_Vertex;
vec4 newPositionX = oldPosition;
newPositionX.y = oldPosition.y * cos(rad_angle_x) - oldPosition.z * sin(rad_angle_x);
newPositionX.z = oldPosition.y * sin(rad_angle_x) + oldPosition.z * cos(rad_angle_x);
float rad_angle_y = angleY * PI / 180.0;
vec4 newPositionXY = newPositionX;
newPositionXY.x = newPositionX.x * cos(rad_angle_y) + newPositionX.z * sin(rad_angle_y);
newPositionXY.z = newPositionX.z * cos(rad_angle_y) - newPositionX.x * sin(rad_angle_y);
gl_Position = gl_ModelViewProjectionMatrix * newPositionXY;
}
This way you don't need to know matrix multiplications.