varying float oz;

#vertex

void main() {
    oz = (gl_Vertex.z + 20.0) * 0.05;
    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_FrontColor = gl_Color;
    gl_Position = ftransform();
}

#fragment

uniform sampler2D tex;

void main() {
    vec4 c = gl_Color * texture2D(tex, vec2(gl_TexCoord[0]));
    float f = max(min(oz, 1.0), 0.0);
    gl_FragColor = c * (f * f);
}