Opengl terrain texture shading

Question

I am currently working on an OpenGL (JOGL) project in java. The goal is to create a terrain with textures and shading.

I'm creating a random simplex noise, using these values as a heightmap. The heights are mapped to a 1D texture to simulate coloring based on height. A material (ambient/diffuse/specular/shininess) is then used to simulate shading.

However; after adding shading to the terrain, 'stripes' appear on each 'column' (Y direction) of the terrain.

The following material is then applied:

TERRAIN(
        new float[]{0.5f, 0.5f, 0.5f, 1.0f},
        new float[]{0.7f, 0.7f, 0.7f, 1.0f},
        new float[]{0.2f, 0.2f, 0.2f, 1.0f},
        new float[]{100f})

The material enum constructor:

Material(float[] ambient, float[] diffuse, float[] specular, float[] shininess) {
    this.ambient = ambient;
    this.diffuse = diffuse;
    this.specular = specular;
    this.shininess = shininess;
}

I apply the material using the following method:

public void use(GL2 gl) {
    // set the material properties
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GLLightingFunc.GL_AMBIENT, ambient, 0);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GLLightingFunc.GL_DIFFUSE, diffuse, 0);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GLLightingFunc.GL_SPECULAR, specular, 0);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GLLightingFunc.GL_SHININESS, shininess, 0);
}

After creating a 2D 'noisearray' consistent of 0-1 values, an 2D vectorarray is created, consiting of X*Y vectors, where each vector represents a point in the plane/terrain.

Here is the method that draws triangles in between those points, where you can see I draw the plane per column (Y direction):

public void draw(GL2 gl, GLU glu, GLUT glut, Drawer drawer) {
    Material.TERRAIN.use(gl);
    texture.bind(gl);
    if (showGrid)
        gl.glPolygonMode( gl.GL_FRONT_AND_BACK, gl.GL_LINE );
    ArrayList<Vector[]> normals = new ArrayList<>();
    for(int i=1;i<vectors.length;i++) {
        gl.glBegin(gl.GL_TRIANGLE_STRIP);
        for (int j = 0; j < vectors[i].length; j++) {
            Vector normalTopRight, normalBottomLeft;

            //Calculate normals top right
            Vector v1, v2, triangleCenterTR;
            if (j < vectors[i].length - 1)
            {
                v1 = vectors[i-1][j].subtract(vectors[i][j]);
                v2 = vectors[i][j+1].subtract(vectors[i][j]);
                normalTopRight = v2.cross(v1).normalized();
                // Get center (a+b+c)*(1/3)
                triangleCenterTR = (vectors[i][j].add(vectors[i - 1][j]).add(vectors[i][j + 1])).scale(1.0 / 3);
            } else {
                v1 = vectors[i-1][j].subtract(vectors[i][j]);
                v2 = vectors[i][j-1].subtract(vectors[i][j]);
                normalTopRight = v1.cross(v2).normalized();
                // Get center (a+b+c)*(1/3)
                triangleCenterTR = (vectors[i][j].add(vectors[i-1][j]).add(vectors[i][j-1])).scale(1.0/3);
            }
            normals.add(new Vector[] {triangleCenterTR, triangleCenterTR.add(normalTopRight)});

            if (j != 0)
            {
                v1 = vectors[i][j].subtract(vectors[i-1][j]);
                v2 = vectors[i-1][j-1].subtract(vectors[i-1][j]);
                normalBottomLeft = v2.cross(v1).normalized();
                // Get center (a+b+c)*(1/3)
                Vector triangleCenterBL = (vectors[i - 1][j].add(vectors[i][j]).add(vectors[i - 1][j - 1])).scale(1.0 / 3);
                normals.add(new Vector[]{triangleCenterBL, triangleCenterBL.add(normalBottomLeft)});
            } else {
                normalBottomLeft = null; // If j==0, there is no bottom left triangle above
            }

            /**
             * We have everything to start drawing
             */
            // Set some color
            if (j == 0) {
                // Initialization vector
                gl.glTexCoord1d(mapTextureToHeight(vectors[i][j].z));
                drawer.glVertexV(vectors[i][j]);
            } else {
                drawer.glNormalV(normalBottomLeft);
            }

            // Shift left
            gl.glTexCoord1d(mapTextureToHeight(vectors[i - 1][j].z));
            drawer.glVertexV(vectors[i - 1][j]);

            // Right down diagonally
            if (j < vectors[i].length - 1) { // Skip if we are reached the end
                gl.glTexCoord1d(mapTextureToHeight(vectors[i][j + 1].z));
                drawer.glNormalV(normalTopRight);
                drawer.glVertexV(vectors[i][j + 1]);
            }
        }
        gl.glEnd();
    }
    if (showGrid)
        gl.glPolygonMode( gl.GL_FRONT_AND_BACK, gl.GL_FILL );
    if (drawNormals) {
        for (Vector[] arrow : normals) {
            if (yellowNormals)
                Material.YELLOW.use(gl);
            else
                gl.glTexCoord1d(mapTextureToHeight(arrow[0].z));
            drawer.drawArrow(arrow[0], arrow[1], 0.05);
        }
    }

    texture.unbind(gl);
}

The most obvious reason for the stripes is the fact I draw the triangles per column, causing OpenGL to not be able to smoothen the shading on the polygons (GL_SMOOTH). Is there any way to fix this?

[Edit1] Copied from your comment by Spektre

I just finished calculating the average normals, I indeed have a smooth terrain now, but the lighting looks kind of dull (no depth)

Here is the new code that draws the terrain:

public void draw() {
    if (showGrid)
        gl.glPolygonMode( gl.GL_FRONT_AND_BACK, gl.GL_LINE);
    texture.bind(gl);
    Material.TERRAIN.use(gl);
    for(int i=1;i<vectors.length;i++) {
        gl.glBegin(gl.GL_TRIANGLE_STRIP);
        for (int j = 0; j < vectors[i].length; j++) {
            // Initialization vector
            gl.glTexCoord1d(mapTextureToHeight(vectors[i][j].z));
            drawer.glNormalV(normals.get(vectors[i][j]));
            drawer.glVertexV(vectors[i][j]);

            // Shift left
            gl.glTexCoord1d(mapTextureToHeight(vectors[i - 1][j].z));
            drawer.glNormalV(normals.get(vectors[i - 1][j]));
            drawer.glVertexV(vectors[i - 1][j]);
        }
        gl.glEnd();
    }
    if (showGrid)
        gl.glPolygonMode( gl.GL_FRONT_AND_BACK, gl.GL_FILL );
    if (drawNormals)
        drawFaceNormals();
    texture.unbind(gl);
}

I cleaned it up, I am sure the normals are pointing the correct way using the drawnormals function and made sure OpenGL is seeing the top of the terrain as FRONT using (gl.GL_FRONT -> draws only above terrain, not below).

Here is the complete class: PasteBin

Answer 1

Thanks to @Spektre for helping me out.

After properly calculating the average normal of all surrounding faces on a vertex and using this normal for glNormal , the shading was correct.