// ================================================================================================
// 
// This file is part of the CAMPVis Software Framework.
// 
// If not explicitly stated otherwise: Copyright (C) 2012, all rights reserved,
//      Christian Schulte zu Berge <christian.szb@in.tum.de>
//      Chair for Computer Aided Medical Procedures
//      Technische Universität München
//      Boltzmannstr. 3, 85748 Garching b. München, Germany
// For a full list of authors and contributors, please refer to the file "AUTHORS.txt".
// 
// The licensing of this softare is not yet resolved. Until then, redistribution in source or
// binary forms outside the CAMP chair is not permitted, unless explicitly stated in legal form.
// However, the names of the original authors and the above copyright notice must retain in its
// original state in any case.
// 
// Legal disclaimer provided by the BSD license:
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY 
// AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR 
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
// 
// ================================================================================================

in vec3 ex_TexCoord;
out vec4 out_Color;

#include "tools/texture2d.frag"

#ifdef REDUCTION_2D
    uniform sampler2D _texture;
    uniform vec2 _texCoordsShift;
#endif

#ifdef REDUCTION_3D
    uniform sampler3D _texture;
    uniform vec2 _texCoordsShift;
    uniform int _textureDepth;
#endif

void main() {
    vec2 tmp = ex_TexCoord.xy - _texCoordsShift;

#ifdef REDUCTION_2D
    // 2D reduction:
    vec4 a = texture(_texture, tmp);
    vec4 b = textureOffset(_texture, tmp, ivec2(1, 0));
    vec4 c = textureOffset(_texture, tmp, ivec2(0, 1));
    vec4 d = textureOffset(_texture, tmp, ivec2(1, 1));
#endif

#ifdef REDUCTION_3D
    // 3D reduction along depth:
    float textureDepthRCP = 1.0 / _textureDepth;

    vec4 a = texture(_texture, vec3(tmp, textureDepthRCP/2.0));
    vec4 b = textureOffset(_texture, vec3(tmp, textureDepthRCP/2.0), ivec3(1, 0, 0));
    vec4 c = textureOffset(_texture, vec3(tmp, textureDepthRCP/2.0), ivec3(0, 1, 0));
    vec4 d = textureOffset(_texture, vec3(tmp, textureDepthRCP/2.0), ivec3(1, 1, 0));

    for (float z = 3.0 * textureDepthRCP / 2.0; z < 1.0; z += textureDepthRCP) {
        a = REDUCTION_OP_2(a, texture(_texture, vec3(tmp, z)));
        b = REDUCTION_OP_2(b, textureOffset(_texture, vec3(tmp, z), ivec3(1, 0, 0)));
        c = REDUCTION_OP_2(c, textureOffset(_texture, vec3(tmp, z), ivec3(0, 1, 0)));
        d = REDUCTION_OP_2(d, textureOffset(_texture, vec3(tmp, z), ivec3(1, 1, 0)));
    }
#endif

    // final reduction of the four pixels
    out_Color = REDUCTION_OP_4(a, b, c, d);
}