To discard fragments based on alpha data from a texture, use the following steps:

1. Use the same vertex and fragment shaders from the Applying a 2D texture recipe. However, make the following modifications to the fragment shader.
2. Replace the sampler2D uniform variable with the following:

layout(binding=0) uniform sampler2D BaseTex; 
layout(binding=1) uniform sampler2D AlphaTex;

3. In the blinnPhong function, use BaseTex to look up the value of the ambient and diffuse reflectivity.
4. Replace the contents of the main function with the following code:

void main() {
    vec4 alphaMap = texture( AlphaTex, TexCoord );

    if(alphaMap.a < 0.15 )
        discard;
    else {
        if( gl_FrontFacing ) {
            FragColor = vec4( 
            blinnPhong(Position,normalize(Normal)), 1.0 );
        } else {
            FragColor = vec4( blinnPhong(Position,normalize(-
            Normal)), 1.0 );
        }
    }
}