//
//  light_directional_osx.fsh
//  Kraken Engine
//
//  Copyright 2021 Kearwood Gilbert. All rights reserved.
//  
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//  
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//  
//  THIS SOFTWARE IS PROVIDED BY KEARWOOD GILBERT ''AS IS'' AND ANY EXPRESS OR IMPLIED
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//


out vec4 colorOut;

uniform sampler2D gbuffer_frame;
uniform sampler2D gbuffer_depth;

uniform mediump vec3 light_direction_view_space; // Must be normalized and converted to view space before entering shader
uniform lowp vec3 light_color;
uniform highp float light_intensity;
uniform mediump vec4 viewport;

void main()
{
    lowp vec2 gbuffer_uv = vec2(gl_FragCoord.xy / viewport.zw);  // FINDME, TODO - Dependent Texture Read adding latency, due to calculation of texture UV within fragment -- move to vertex shader?
    lowp vec4 gbuffer_sample = texture(gbuffer_frame, gbuffer_uv);
    
    mediump vec3 gbuffer_normal = normalize(2.0 * gbuffer_sample.rgb - 1.0);
    mediump float gbuffer_specular_exponent = gbuffer_sample.a * 100.0;
    
    mediump vec3 view_space_vertex_position = vec3(
        ((2.0 * gl_FragCoord.xy) - (2.0 * viewport.xy)) / (viewport.zw) - 1.0,
        (2.0 * -texture(gbuffer_depth, gbuffer_uv).r - gl_DepthRange.near - gl_DepthRange.far) / (gl_DepthRange.far - gl_DepthRange.near)
    );
    
    //mediump float lamberFactor = max(0.0,dot(light_direction_view_space, gbuffer_normal)) * 0.2;
    mediump float lamberFactor = dot(light_direction_view_space, gbuffer_normal) * 0.2;

    mediump float specularFactor = 0.0;

    mediump vec3 halfVec = normalize((normalize(- view_space_vertex_position) + light_direction_view_space)); // Normalizing anyways, no need to divide by 2
    specularFactor = pow(dot(halfVec,gbuffer_normal), gbuffer_specular_exponent);

    
    colorOut = vec4(light_color * lamberFactor, specularFactor) * light_intensity;
}