Moving Camera in OpenGL - c++

Question

I am working on rendering a terrain in OpenGL.
My code is the following:
void Render_Terrain(int k)
{
GLfloat angle = (GLfloat) (k/40 % 360);
//PROJECTION
glm::mat4 Projection = glm::perspective(45.0f, 1.0f, 0.1f, 100.0f);
//VIEW
glm::mat4 View = glm::mat4(1.);
//ROTATION
//View = glm::rotate(View, angle * -0.1f, glm::vec3(1.f, 0.f, 0.f));
//View = glm::rotate(View, angle * 0.2f, glm::vec3(0.f, 1.f, 0.f));
//View = glm::rotate(View, angle * 0.9f, glm::vec3(0.f, 0.f, 1.f));
View = glm::translate(View, glm::vec3(0.f,0.f, -4.0f)); // x, y, z position ?
//MODEL
glm::mat4 Model = glm::mat4(1.0);
glm::mat4 MVP = Projection * View * Model;
glUniformMatrix4fv(glGetUniformLocation(shaderprogram, "MVP_matrix"), 1, GL_FALSE, glm::value_ptr(MVP));
//Transfer additional information to the vertex shader
glm::mat4 MV = Model * View;
glUniformMatrix4fv(glGetUniformLocation(shaderprogram, "MV_matrix"), 1, GL_FALSE, glm::value_ptr(MV));
glClearColor(0.0, 0.0, 0.0, 1.0);
glDrawArrays(GL_LINE_STRIP, terrain_start, terrain_end );
}
I can do a rotation around the X,Y,Z axis, scale my terrain but I can't find a way to move the camera. I am using OpenGL 3+ and I am kinda new to graphics.

Answer 1

The best way to move the camera would be through the use of gluLookAt(), it simulates camera movement since the camera cannot be moved whatsoever. The function takes 9 parameters. The first 3 are the XYZ coordinates of the eye which is where the camera is exactly located. The second 3 parameters are the XYZ coordinates of the center which is the point the camera is looking at from the eye. It is always going to be the center of the screen. The third 3 parameters are the XYZ coordinates of the UP vector which points vertically upwards from the eye. Through manipulating those 3 XYZ coordinates you can simulate any camera movement you want.
Check out this link.
Further details:
-If you want for example to rotate around an object you rotate your eye around the up vector.
-If you want to move forward or backwards you add or subtract to the eye as well as the center points.
-If you want to tilt the camera left or right you rotate your up vector around your look vector where your look vector is center - eye.
gluLookAt operates on the deprecated fixed function pipeline, so you should use glm::lookAt instead.

Answer 2

You are currently using a constant vector for translation. In the commented out code (which I assume you were using to test rotation), you use angle to adjust the rotation. You should have a similar variable for translation. Then, you can change the glm::translate call to:
View = glm::translate(View, glm::vec3(x_transform, y_transform, z_transform)); // x, y, z position ?
and get translation.
You should probably pass in more than one parameter into Render_Terrain, as translation and rotation need at least six parameters.

Answer 3

In OpenGL the camera is always at (0, 0, 0). You need to set the matrix mode to GL_MODELVIEW, and then modify or set the model/view matrix using things like glTranslate, glRotate, glLoadMatrix, etc. in order to make it appear that the camera has moved. If you're using GLU, you can use gluLookAt to point the camera in a particular direction.