shader_type spatial;
render_mode unshaded, cull_back, depth_draw_opaque;

// Wave parameters: wave.xy is direction, wave.z is steepness, wave.w is wavelength.
uniform vec4 color:source_color = vec4(0.13, 0.31, 0.53, 0.95);
uniform vec4 wave = vec4(1.0, 0.0, 0.5, 10.0);
uniform float wave_speed : hint_range(0.0, 5.0) = 1.0;
uniform float gravity : hint_range(0.0, 20.0) = 9.8;
uniform float wave_time;


vec3 gerstnerWave(vec3 p, out vec3 tangent, out vec3 binormal) {
    float steepness = wave.z;
    float wavelength = wave.w;
    float k = 2.0 * PI / wavelength;
    float c = sqrt(gravity / k);
    vec2 d = normalize(wave.xy);
    float f = k * ( dot(d, p.xz) - c * wave_time * wave_speed );
    float a = steepness / k;
    
    // Update tangent and binormal for lighting or other effects.
    tangent = vec3(
        -d.x * d.x * (steepness * sin(f)),
         d.x * (steepness * cos(f)),
        -d.x * d.y * (steepness * sin(f))
    );
    binormal = vec3(
        -d.x * d.y * (steepness * sin(f)),
         d.y * (steepness * cos(f)),
        -d.y * d.y * (steepness * sin(f))
    );
    
    return vec3(
        d.x * (a * cos(f)),
        a * sin(f),
        d.y * (a * cos(f))
    );
}

void vertex() {
    vec3 tangent;
    vec3 binormal;
    vec3 disp = gerstnerWave(VERTEX, tangent, binormal);
    VERTEX.xyz += disp;
}

void fragment() {
	ALBEDO = color.rgb;
	ALPHA = color.a;
}