Transparent Shader using GLSL - opengl-es

Question

I'm having a problem with fragment shader as you can see in the image below.
I don't want to render the parts that are in red in the image
I have to passes which culls clockwise and anticlockwise
and I'm getting the dot product of the normal with the camera position
if its less than 0 I set a transparent fragment
otherwise discard the fargment
here is the shader
#version 100
precision mediump float;
varying float lightDiffuse;
void main()
{
float light = ( 1.0 - lightDiffuse) * 0.5;
vec3 lightColor = vec3(0.0,1.0,1.0);
vec3 diffuseColor = lightColor * light ;
vec4 c;
if(lightDiffuse <0.0 )
{
// back faces, opaque
// front faces, very transparent
c = vec4(diffuseColor, 0.2);
}
else
{
discard;
}
gl_FragColor = c;
}
#version 100
#define lowp
#define mediump
#define highp
attribute vec4 vertex;
attribute vec3 normal;
uniform mat4 normalMatrix;
uniform mat4 modelViewProjectionMatrix;
uniform mat4 modelView;
uniform vec3 camera_world_position;
varying highp float lightDiffuse;
void main()
{
gl_Position = modelViewProjectionMatrix * vertex;
vec3 norm = normal;
norm *=-1.0;
lightDiffuse = dot(normalize(vec3(norm.x, norm.y, norm.z)), normalize(camera_world_position));
}
here is the material script
material 44267_1508405690_0##carpaint
{
technique
{
pass
{
cull_hardware anticlockwise
scene_blend alpha_blend
vertex_program_ref char_shader2_vs100
{
param_named_auto modelViewProjectionMatrix worldviewproj_matrix
param_named_auto normalMatrix inverse_transpose_world_matrix
param_named_auto modelView worldview_matrix
param_named_auto camera_world_position camera_position
}
fragment_program_ref char_shader2_fs100
{
}
}
pass
{
cull_hardware clockwise
vertex_program_ref char_shader2_vs100
{
param_named_auto modelViewProjectionMatrix worldviewproj_matrix
param_named_auto normalMatrix inverse_transpose_world_matrix
param_named_auto modelView worldview_matrix
param_named_auto camera_world_position camera_position
}
fragment_program_ref char_shader2_fs100
{
}
}
}
}

Answer 1

If you want to cull occluded triangles, allocate a depth buffer and use a depth test, it's what it exists for.
Don't do facing tests in the fragment shader, that's not necessary and horribly expensive, just enable GL_CULL_FACE and set the front face correctly. Note that not all models downloaded off the internet get this right, so you might have an input model with broken winding for some triangles.