/***********************************************************************************
 *                                                                                 *
 * Voreen - The Volume Rendering Engine                                            *
 *                                                                                 *
 * Copyright (C) 2005-2018 University of Muenster, Germany,                        *
 * Department of Computer Science.                                                 *
 * For a list of authors please refer to the file "CREDITS.txt".                   *
 *                                                                                 *
 * This file is part of the Voreen software package. Voreen is free software:      *
 * you can redistribute it and/or modify it under the terms of the GNU General     *
 * Public License version 2 as published by the Free Software Foundation.          *
 *                                                                                 *
 * Voreen is distributed in the hope that it will be useful, but WITHOUT ANY       *
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR   *
 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.      *
 *                                                                                 *
 * You should have received a copy of the GNU General Public License in the file   *
 * "LICENSE.txt" along with this file. If not, see <http://www.gnu.org/licenses/>. *
 *                                                                                 *
 * For non-commercial academic use see the license exception specified in the file *
 * "LICENSE-academic.txt". To get information about commercial licensing please    *
 * contact the authors.                                                            *
 *                                                                                 *
 ***********************************************************************************/

#version 330

#include "mod_geometryoutput.frag"
#include "modules/mod_sampler2d.frag"
#include "modules/mod_shading.frag"

in FragStruct {
  vec4 posEye;
  vec4 color;
#if defined(USE_NORMAL)
  vec3 normal;
#endif
#if defined(USE_TEXCOORD)
  vec2  texCoord;
  flat ivec2 texIndex;
#endif
} fragData;

uniform vec3 lightPositionEye_;
uniform bool enableLighting_;

#if defined(USE_TEXCOORD) && defined(USE_TEXTURE_ARRAY)
uniform sampler2DArray textures_;
#elif defined(USE_TEXCOORD) && defined(USE_SINGLE_TEXTURE)
uniform sampler2D texture_;
#endif

//const int hashPos[37] = int[](0, 0, 1, 26, 2, 23, 27, 0, 3, 16, 24, 30, 28, 11, 0, 13, 4, 7, 17, 0, 25, 22, 31, 15, 29, 10, 12, 6, 0, 21, 14, 9, 5, 20, 8, 19, 18);

void main() {
#if defined(USE_TEXCOORD) && defined(USE_TEXTURE_ARRAY)
    // texturing was enabled, but no texture coordinates were defined -> discard fragment
    if(fragData.texIndex.y == 0)
        discard;
#endif

#if defined(USE_NORMAL)
    vec3 norm = normalize(fragData.normal);
#endif

#if defined(USE_TEXCOORD) && defined(USE_TEXTURE_ARRAY)
    vec4 ambCol = vec4(0.0);
    vec4 difCol = vec4(0.0);
    vec4 spcCol = vec4(0.0);
    bool ambColSet = false;
    bool difColSet = false;
    bool spcColSet = false;

    int usedTextures = fragData.texIndex.x;
    int textureApplications = fragData.texIndex.y;
    int counter = 0;

    while(usedTextures != 0 && counter < 4) {
        // calculate int where the lowest bit that was set in the original int is deleted
        int tmp = int(usedTextures & int(usedTextures - 1));
        // calculate int containing only the previously deleted bit, take log2 to calculate layer in texture stack
        float texNum = log2(float(usedTextures - tmp));
        //float texNum = float(hashPos[(usedTextures - tmp) % 37]);
        // look up corresponding color in the stack
        vec4 texCol = texture(textures_, vec3(fragData.texCoord, texNum));
        // make sure that tex color is visible if set
        if(texCol.rgb != vec3(0.0) && texCol.a == 0.0)
            texCol.a = 1.0;

        // find out what this texture does by looking up the 4 corresponding texture function bits
        int textureFunction = int(textureApplications >> (counter * 4)) % 16;
        // ambient color
        if(int(textureFunction & 1) > 0) {
            ambCol = combineColorAndTexture(fragData.color, texCol);
            ambColSet = true;
        }
        // diffuse color
        if(int(textureFunction & 2) > 0) {
            difCol = combineColorAndTexture(fragData.color, texCol);
            difColSet = true;
        }
        // specular color
        if(int(textureFunction & 4) > 0) {
            spcCol = texCol;
            spcColSet = true;
        }

        // normal map
        // TODO differ from / support simpler one-channel bump-mapping
        if(int(textureFunction & 8) > 0) {
            // rotate normal read from geometry map to local coordinate system defined by geometry normal
            vec3 localNorm = normalize(2.0 * texCol.xyz - 1.0);
            vec3 tang = normalize(cross(norm, vec3(0.0, 1.0, 0.0)));
            vec3 btang = normalize(cross(norm, tang));
            //mat3 rot = transpose(mat3(tang, btang, fragData.normal));
            mat3 rot = mat3(tang, btang, norm);
            norm = rot * localNorm;
        }

        usedTextures = tmp;
        counter++;
    }

    // use same color for diffuse and ambient term if only one was set
    if(!ambColSet && difColSet)
        ambCol = difCol;
    else if(!difColSet && ambColSet)
        difCol = ambCol;

    // use default specular color white if not set
    if(!spcColSet)
        spcCol = vec4(1.0);
#elif defined(USE_TEXCOORD) && defined(USE_SINGLE_TEXTURE)
    vec4 texCol = vec4(texture(texture_, fragData.texCoord).xyz, 1.0);
    vec4 ambCol = combineColorAndTexture(fragData.color, texCol);
    vec4 difCol = combineColorAndTexture(fragData.color, texCol);
    vec4 spcCol = vec4(1.0);
#else
    vec4 ambCol = fragData.color;
    vec4 difCol = fragData.color;
    vec4 spcCol = vec4(1.0);
#endif

    vec4 result = ambCol;

#if defined(USE_NORMAL)
    if(enableLighting_)
        result.xyz = phongShading(norm, fragData.posEye.xyz, lightPositionEye_, vec3(0.0), ambCol.rgb, difCol.rgb, spcCol.rgb);
#endif

    outputFragment(result);
}
