Stop LibGDX rendering faces inside objects - opengl

Question

So by default, libgdx renders both sides of a face. When you make a cube using a mesh (supplying vertices and indices), it renders the faces inside the cube (wasting render time).
I want to stop this because it wastes render time when I have x amount of voxels on the screen.
I have tried face culling but it's completely broken. It removes the sides and everything.
Here's my code:
public void setup() {
String vertexShader = "attribute vec4 a_position; \n" + "attribute vec4 a_color;\n" + "attribute vec2 a_texCoord0;\n" + "uniform mat4 u_projTrans;\n" + "varying vec4 v_color;" + "varying vec2 v_texCoords;" + "void main() \n" + "{ \n" + " v_color = vec4(1, 1, 1, 1); \n" + " v_texCoords = a_texCoord0; \n" + " gl_Position = u_projTrans * a_position; \n" + "} \n";
String fragmentShader = "#ifdef GL_ES\n" + "precision mediump float;\n" + "#endif\n" + "varying vec4 v_color;\n" + "varying vec2 v_texCoords;\n" + "uniform sampler2D u_texture;\n" + "void main() \n" + "{ \n" + " gl_FragColor = v_color * texture2D(u_texture, v_texCoords);\n" + "}";
shader = new ShaderProgram(vertexShader, fragmentShader);
float[] vertices = { -0.5f, 0.5f, -0.5f, 0, 0, -0.5f, -0.5f, -0.5f, 0, 1, 0.5f, -0.5f, -0.5f, 1, 1, 0.5f, 0.5f, -0.5f, 1, 0, -0.5f, 0.5f, 0.5f, 0, 0, -0.5f, -0.5f, 0.5f, 0, 1, 0.5f, -0.5f, 0.5f, 1, 1, 0.5f, 0.5f, 0.5f, 1, 0, 0.5f, 0.5f, -0.5f, 0, 0, 0.5f, -0.5f, -0.5f, 0, 1, 0.5f, -0.5f, 0.5f, 1, 1, 0.5f, 0.5f, 0.5f, 1, 0, -0.5f, 0.5f, -0.5f, 0, 0, -0.5f, -0.5f, -0.5f, 0, 1, -0.5f, -0.5f, 0.5f, 1, 1, -0.5f, 0.5f, 0.5f, 1, 0, -0.5f, 0.5f, 0.5f, 0, 0, -0.5f, 0.5f, -0.5f, 0, 1, 0.5f, 0.5f, -0.5f, 1, 1, 0.5f, 0.5f, 0.5f, 1, 0, -0.5f, -0.5f, 0.5f, 0, 0, -0.5f, -0.5f, -0.5f, 0, 1, 0.5f, -0.5f, -0.5f, 1, 1, 0.5f, -0.5f, 0.5f, 1, 0
};
short[] indices = { 0, 1, 3, 3, 1, 2, 4, 5, 7, 7, 5, 6, 8, 9, 11, 11, 9, 10, 12, 13, 15, 15, 13, 14, 16, 17, 19, 19, 17, 18, 20, 21, 23, 23, 21, 22
};
texture = new Texture("texture.png");
Gdx.input.setCursorCatched(false);
mesh = new Mesh(true, vertices.length / 3, indices.length, VertexAttribute.Position(), VertexAttribute.TexCoords(0));
mesh.setVertices(vertices);
mesh.setIndices(indices);
GL40.glEnable(GL40.GL_DEPTH_TEST);
//GL40.glEnable(GL40.GL_CULL_FACE);
//GL40.glCullFace(GL40.GL_BACK);
}
public void render() {
Gdx.gl.glClearColor(0.1f, 0.1f, 0.1f, 1f);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);
cameraController.update();
texture.bind();
shader.begin();
shader.setUniformMatrix("u_projTrans", camera.combined);
shader.setUniformi("u_texture", 0);
mesh.render(shader, GL46.GL_TRIANGLES);
shader.end();
}

Answer 1

When Face Culling is enabled then then primitives are discarded, dependent on the winding order of the vertex coordinates, as seen from the point of view.
For this a winding order for the front faces is defined, by glFrontFace. By default this is counter clockwise.
If back faces sculling is enabled:
GL40.glEnable(GL40.GL_CULL_FACE);
GL40.glCullFace(GL40.GL_BACK);
then the polygons which have the opposite winding order (clockwise) are discarded.
According to your vertex coordinates
float[] vertices = {
-0.5f, 0.5f, -0.5f, 0, 0,
-0.5f, -0.5f, -0.5f, 0, 1,
0.5f, -0.5f, -0.5f, 1, 1,
0.5f, 0.5f, -0.5f, 1, 0,
-0.5f, 0.5f, 0.5f, 0, 0,
-0.5f, -0.5f, 0.5f, 0, 1,
0.5f, -0.5f, 0.5f, 1, 1,
0.5f, 0.5f, 0.5f, 1, 0,
0.5f, 0.5f, -0.5f, 0, 0,
0.5f, -0.5f, -0.5f, 0, 1,
0.5f, -0.5f, 0.5f, 1, 1,
0.5f, 0.5f, 0.5f, 1, 0,
-0.5f, 0.5f, -0.5f, 0, 0,
-0.5f, -0.5f, -0.5f, 0, 1,
-0.5f, -0.5f, 0.5f, 1, 1,
-0.5f, 0.5f, 0.5f, 1, 0,
-0.5f, 0.5f, 0.5f, 0, 0,
-0.5f, 0.5f, -0.5f, 0, 1,
0.5f, 0.5f, -0.5f, 1, 1,
0.5f, 0.5f, 0.5f, 1, 0,
-0.5f, -0.5f, 0.5f, 0, 0,
-0.5f, -0.5f, -0.5f, 0, 1,
0.5f, -0.5f, -0.5f, 1, 1,
0.5f, -0.5f, 0.5f, 1, 0
};
and indices
short[] indices = {
0, 1, 3, 3, 1, 2,
4, 5, 7, 7, 5, 6,
8, 9, 11, 11, 9, 10,
12, 13, 15, 15, 13, 14,
16, 17, 19, 19, 17, 18,
20, 21, 23, 23, 21, 22
};
This means that the 1st, 3rd and 5th row of indices have the wrong winding order. It has to be:
short[] indices = {
0, 3, 1, 3, 2, 1,
4, 5, 7, 7, 5, 6,
8, 11, 9, 11, 10, 9,
12, 13, 15, 15, 13, 14,
16, 19, 17, 19, 18, 17,
20, 21, 23, 23, 21, 22
};