How does one restrict drawing in OpenGL between two coordinates in the axis?

Question

I'm a new opengl programmer. I am plotting a height map composed of thousands of triangles in a 3D graph format. They are scaled so that they are plotted between -1 and +1 in the three axis. Now I am able to zoom in the X axis only and am able to translate in the X axis as well by applying the appropriate scale and translation matrices. This effectively allows me to zoom right into the data and move it in the x direction as I choose. The problem is, once I zoom, the data in the x direction now extends outside the -1 to + 1 region which the boundaries of a graph. I want this data to not be shown. How is this done in modern OpenGL? Thank you Edit: The matrices are as follows:

        plottingProgram["projection_matrix"].SetValue(Matrix4.CreatePerspectiveFieldOfView(0.45f, (float)width / height, 0.1f, 1000f));
        plottingProgram["view_matrix"].SetValue(Matrix4.LookAt(new Vector3(0, 0, 10), Vector3.Zero, new Vector3(0, 1, 0)));

and the vertex shader is

    public static string VertexShader = @"
    #version 130

    in vec3 vertexPosition;

    out vec2 textureCoordinate;

    uniform mat4 projection_matrix;
    uniform mat4 view_matrix;
    uniform mat4 model_matrix;

    void main(void)
    {
        textureCoordinate = vertexPosition.xy;
        gl_Position = projection_matrix * view_matrix * model_matrix * vec4(vertexPosition, 1);           
    }
    ";

Here is a link to the graph: http://va2fsq.com/wp-content/uploads/graph.jpg

Thanks

Answer 1

I solved this. After trying many things like glScissor, I happened upon the glClip_distance. So my initial try placed a Uniform in the shader which was set to

in vec3 vertexPosition;
uniform vec4 plane0 = (-1,0,0,1);
uniform vec4 plane1 = (1,0,0,1);

void main(void)
{ 
   gl_ClipDistance[0] = dot(vec4(vertexPosition,1), plane0;
   gl_ClipDistance[1] = dot(vec4(vertexPosition,1), plane2;

Now the problem with this is that the vec4 planes are scaled and translated by any model matrix scaling or transformations. So that wouldn't work. So the solution is to move the clip vectors outside of the vertex shader and apply the opposite scaling to them as follows:

        Vector4 clip1 = new Vector4(-1, 0, 0, 1.0f / scale); 
        Vector4 clip2 = new Vector4(1, 0, 0, 1.0f / scale);

        plottingProgram["model_matrix"].SetValue(Matrix4.CreateScaling(new Vector3(scale,1,1)) * Matrix4.CreateTranslation(new Vector3(0,0,0)) *Matrix4.CreateRotationY(yangle) * Matrix4.CreateRotationX(xangle));
        plottingProgram["plane0"].SetValue(clip1);
        plottingProgram["plane1"].SetValue(clip2);

and the complete vertex shader is given by

    public static string VertexShader = @"
    #version 130

    in vec3 vertexPosition;

    out vec2 textureCoordinate;

    uniform mat4 projection_matrix;
    uniform mat4 view_matrix;
    uniform mat4 model_matrix;

    uniform vec4 plane0;
    uniform vec4 plane1;

    void main(void)
    {
        textureCoordinate = vertexPosition.xy;

        gl_ClipDistance[0] = dot(vec4(vertexPosition,1), plane0);
        gl_ClipDistance[1] = dot(vec4(vertexPosition,1), plane1);

        gl_Position = projection_matrix * view_matrix * model_matrix * vec4(vertexPosition, 1);  
    }
    ";

You can also translate in the same way.