#version 120
//#version 130 // use with version 1

uniform highp float lightStrength;
uniform highp float ambientStrength;
uniform highp float shadowQuality;
uniform highp vec3 color_mdl;
uniform highp sampler2DShadow shadowMap; // use with version 2
//uniform highp sampler2D shadowMap; // use with version 1

varying highp vec4 shadowCoord;
varying highp vec3 position_wrld;
varying highp vec3 normal_cmr;
varying highp vec3 eyeDirection_cmr;
varying highp vec3 lightDirection_cmr;
varying highp vec2 coords_mdl;

const highp vec2 poissonDisk[16] = vec2[](vec2(-0.94201624, -0.39906216),
                                          vec2(0.94558609, -0.76890725),
                                          vec2(-0.094184101, -0.92938870),
                                          vec2(0.34495938, 0.29387760),
                                          vec2(-0.91588581, 0.45771432),
                                          vec2(-0.81544232, -0.87912464),
                                          vec2(-0.38277543, 0.27676845),
                                          vec2(0.97484398, 0.75648379),
                                          vec2(0.44323325, -0.97511554),
                                          vec2(0.53742981, -0.47373420),
                                          vec2(-0.26496911, -0.41893023),
                                          vec2(0.79197514, 0.19090188),
                                          vec2(-0.24188840, 0.99706507),
                                          vec2(-0.81409955, 0.91437590),
                                          vec2(0.19984126, 0.78641367),
                                          vec2(0.14383161, -0.14100790));

/*float random(vec3 seed, int i) {
    vec4 seed4 = vec4(seed, i);
    float dot_product = dot(seed4, vec4(12.9898, 78.233, 45.164, 94.673));
    return fract(sin(dot_product) * 43758.5453);
}*/

// Version 1: Causes self-shadowing, but shadows are smooth
/*void main() {
    float shadowFactor = 1.0; // default to '1' meaning "no shadow"
    vec4 shadCoordsPD = shadowCoord;
    shadCoordsPD.z += 0.005;
    shadCoordsPD /= shadowCoord.w;
    if (shadowCoord.w <= 0.0) { // ignore negative projection
        shadowFactor = 1.0;
    } else if (shadCoordsPD.x < 0.0 || shadCoordsPD.y < 0.0) { // outside light frustum, ignore
        shadowFactor = 1.0;
    } else if (shadCoordsPD.x >= 1.0 || shadCoordsPD.y >= 1.0) { // outside light frustum, ignore
        shadowFactor = 1.0;
    } else {
        // This does not work perfectly. It causes self-shadowing, which we should get rid of.
        // Requires at least #version 130
        float shadow = 0.0;
        shadow += textureProjOffset(shadowMap, shadCoordsPD, ivec2(0, 0));
        shadow += textureProjOffset(shadowMap, shadCoordsPD, ivec2(-1, 1));
        shadow += textureProjOffset(shadowMap, shadCoordsPD, ivec2(1, 1));
        shadow += textureProjOffset(shadowMap, shadCoordsPD, ivec2(-1, -1));
        shadow += textureProjOffset(shadowMap, shadCoordsPD, ivec2(1, -1));
        shadow *= 0.2;
        shadowFactor = shadow;
    }

    highp vec3 materialDiffuseColor = vec3(coords_mdl.y * color_mdl.x, coords_mdl.y * color_mdl.y, coords_mdl.y * color_mdl.z);
    highp vec3 materialAmbientColor = vec3(ambientStrength, ambientStrength, ambientStrength) * materialDiffuseColor;
    highp vec3 materialSpecularColor = vec3(1.0, 1.0, 1.0);

    highp vec3 n = normalize(normal_cmr);
    highp vec3 l = normalize(lightDirection_cmr);
    highp float cosTheta = clamp(dot(n, l), 0.0, 1.0);

    highp vec3 E = normalize(eyeDirection_cmr);
    highp vec3 R = reflect(-l, n);
    highp float cosAlpha = clamp(dot(E, R), 0.0, 1.0);

    // Shadow strength can be adjusted by using pow(shadowFactor, strength), but it causes self-shadowing issues that need to be solved
    gl_FragColor.rgb =
        shadowFactor * (materialAmbientColor +
        materialDiffuseColor * lightStrength * cosTheta +
        materialSpecularColor * lightStrength * pow(cosAlpha, 20));
    gl_FragColor.a = 1.0;
}*/

// Version 2: Shadows are a bit rugged (may be fixed with poisson disk?)
void main() {
    highp vec3 materialDiffuseColor = vec3(coords_mdl.y * color_mdl.x, coords_mdl.y * color_mdl.y, coords_mdl.y * color_mdl.z);
    highp vec3 materialAmbientColor = vec3(ambientStrength, ambientStrength, ambientStrength) * materialDiffuseColor;
    highp vec3 materialSpecularColor = vec3(1.0, 1.0, 1.0);

    highp vec3 n = normalize(normal_cmr);
    highp vec3 l = normalize(lightDirection_cmr);
    highp float cosTheta = clamp(dot(n, l), 0.0, 1.0);

    highp vec3 E = normalize(eyeDirection_cmr);
    highp vec3 R = reflect(-l, n);
    highp float cosAlpha = clamp(dot(E, R), 0.0, 1.0);

    highp float bias = 0.005 * tan(acos(cosTheta));
    bias = clamp(bias, 0.0, 0.01);

    vec4 shadCoords = shadowCoord;
    shadCoords.z -= bias;
    // adjust shadow strength by increasing the multiplier and lowering the addition (their sum must be 1)
    // direct method; needs large shadow texture to look good
    //highp float visibility = 0.75 * shadow2DProj(shadowMap, shadCoords).r + 0.25;
    // poisson disk sampling; smoothes edges
    highp float visibility = 0.2;
    for (int i = 0; i < 15; i++) {
        vec4 shadCoordsPD = shadCoords;
        shadCoordsPD.x += cos(poissonDisk[i].x) / shadowQuality;
        shadCoordsPD.y += sin(poissonDisk[i].y) / shadowQuality;
        visibility += 0.05 * shadow2DProj(shadowMap, shadCoordsPD).r;
    }
    /*for (int i = 0; i < 15; i++) {
        vec4 shadCoordsPD = shadCoords;
        int index = int(16.0 * random(gl_FragCoord.xyy, i));
        shadCoordsPD.xy += poissonDisk[index] / 150.0;
        visibility += 0.05 * shadow2DProj(shadowMap, shadCoordsPD).r;
    }*/

    gl_FragColor.rgb =
        visibility * (materialAmbientColor +
        materialDiffuseColor * lightStrength * cosTheta +
        materialSpecularColor * lightStrength * pow(cosAlpha, 10));
    gl_FragColor.a = 1.0;
}