uniform mat4 u_matrix;
uniform vec3 u_lightcolor;
uniform lowp vec3 u_lightpos;
uniform lowp float u_lightintensity;
uniform float u_vertical_gradient;
uniform lowp float u_opacity;

attribute vec4 a_pos_normal_ed;
attribute vec2 a_centroid_pos;

varying vec4 v_color;

#pragma mapbox: define highp float base
#pragma mapbox: define highp float height

#pragma mapbox: define highp vec4 color

void main() {
    #pragma mapbox: initialize highp float base
    #pragma mapbox: initialize highp float height
    #pragma mapbox: initialize highp vec4 color

    vec3 pos_nx = floor(a_pos_normal_ed.xyz * 0.5);
    // The least significant bits of a_pos_normal_ed.xy hold:
    // x is 1 if it's on top, 0 for ground.
    // y is 1 if the normal points up, and 0 if it points to side.
    // z is sign of ny: 1 for positive, 0 for values <= 0.
    mediump vec3 top_up_ny = a_pos_normal_ed.xyz - 2.0 * pos_nx;

    float x_normal = pos_nx.z / 8192.0;
    vec3 normal = top_up_ny.y == 1.0 ? vec3(0.0, 0.0, 1.0) : normalize(vec3(x_normal, (2.0 * top_up_ny.z - 1.0) * (1.0 - abs(x_normal)), 0.0));

    base = max(0.0, base);
    height = max(0.0, height);

    float t = top_up_ny.x;

#ifdef TERRAIN
    vec2 centroid_pos = a_centroid_pos;
    bool flat_roof = centroid_pos.x != 0.0;
    float ele = elevation(pos_nx.xy);
    float hidden = float(centroid_pos.x == 0.0 && centroid_pos.y == 1.0);
    float c_ele = flat_roof ? centroid_pos.y == 0.0 ? elevationFromUint16(centroid_pos.x) : flatElevation(centroid_pos) : ele;
    // If centroid elevation lower than vertex elevation, roof at least 2 meters height above base.
    float h = flat_roof ? max(c_ele + height, ele + base + 2.0) : ele + (t > 0.0 ? height : base == 0.0 ? -5.0 : base);
    vec3 pos = vec3(pos_nx.xy, h);
    gl_Position = mix(u_matrix * vec4(pos, 1), AWAY, hidden);
#else
    vec3 pos = vec3(pos_nx.xy, t > 0.0 ? height : base);
    gl_Position = u_matrix * vec4(pos, 1);
#endif

    // Relative luminance (how dark/bright is the surface color?)
    float colorvalue = color.r * 0.2126 + color.g * 0.7152 + color.b * 0.0722;

    v_color = vec4(0.0, 0.0, 0.0, 1.0);

    // Add slight ambient lighting so no extrusions are totally black
    vec4 ambientlight = vec4(0.03, 0.03, 0.03, 1.0);
    color += ambientlight;

    // Calculate cos(theta), where theta is the angle between surface normal and diffuse light ray
    float directional = clamp(dot(normal, u_lightpos), 0.0, 1.0);

    // Adjust directional so that
    // the range of values for highlight/shading is narrower
    // with lower light intensity
    // and with lighter/brighter surface colors
    directional = mix((1.0 - u_lightintensity), max((1.0 - colorvalue + u_lightintensity), 1.0), directional);

    // Add gradient along z axis of side surfaces
    if (normal.y != 0.0) {
        // This avoids another branching statement, but multiplies by a constant of 0.84 if no vertical gradient,
        // and otherwise calculates the gradient based on base + height
        directional *= (
            (1.0 - u_vertical_gradient) +
            (u_vertical_gradient * clamp((t + base) * pow(height / 150.0, 0.5), mix(0.7, 0.98, 1.0 - u_lightintensity), 1.0)));
    }

    // Assign final color based on surface + ambient light color, diffuse light directional, and light color
    // with lower bounds adjusted to hue of light
    // so that shading is tinted with the complementary (opposite) color to the light color
    v_color.rgb += clamp(color.rgb * directional * u_lightcolor, mix(vec3(0.0), vec3(0.3), 1.0 - u_lightcolor), vec3(1.0));
    v_color *= u_opacity;

#ifdef FOG
    v_fog_pos = fog_position(pos);
#endif
}