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;

in vec2 a_pos;
in vec4 a_normal_ed;

#ifdef TERRAIN3D
    in vec2 a_centroid;
#endif


out 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 normal = a_normal_ed.xyz;

    #ifdef TERRAIN3D
	// Raise the "ceiling" of elements by the elevation of the centroid, in meters.
        float height_terrain3d_offset = get_elevation(a_centroid);
	// To avoid having buildings "hang above a slope", create a "basement"
	// by lowering the "floor" of ground-level (and below) elements.
	// This is in addition to the elevation of the centroid, in meters.
        float base_terrain3d_offset = height_terrain3d_offset - (base > 0.0 ? 0.0 : 10.0);
    #else
        float height_terrain3d_offset = 0.0;
        float base_terrain3d_offset = 0.0;
    #endif
    // Sub-terranian "floors and ceilings" are clamped to ground-level.
    // 3D Terrain offsets, if applicable, are applied on the result.
    base = max(0.0, base) + base_terrain3d_offset;
    height = max(0.0, height) + height_terrain3d_offset;

    float t = mod(normal.x, 2.0);

    gl_Position = u_matrix * vec4(a_pos, t > 0.0 ? height : base, 1);

    // 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 / 16384.0, 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.r += clamp(color.r * directional * u_lightcolor.r, mix(0.0, 0.3, 1.0 - u_lightcolor.r), 1.0);
    v_color.g += clamp(color.g * directional * u_lightcolor.g, mix(0.0, 0.3, 1.0 - u_lightcolor.g), 1.0);
    v_color.b += clamp(color.b * directional * u_lightcolor.b, mix(0.0, 0.3, 1.0 - u_lightcolor.b), 1.0);
    v_color *= u_opacity;
}