/** 
 * @file class1\deferred\pbrterrainUtilF.glsl
 *
 * $LicenseInfo:firstyear=2023&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2023, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

/**
 * Triplanar mapping implementation adapted from Inigo Quilez' example shader,
 * MIT license.
 * https://www.shadertoy.com/view/MtsGWH
 * Copyright © 2015 Inigo Quilez
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions: The above copyright
 * notice and this permission notice shall be included in all copies or
 * substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS",
 * WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


in vec3 vary_vertex_normal;

vec3 srgb_to_linear(vec3 c);

float terrain_mix(vec4 samples, float alpha1, float alpha2, float alphaFinal)
{
    return mix( mix(samples.w, samples.z, alpha2), mix(samples.y, samples.x, alpha1), alphaFinal );
}

vec3 terrain_mix(vec3[4] samples, float alpha1, float alpha2, float alphaFinal)
{
    return mix( mix(samples[3], samples[2], alpha2), mix(samples[1], samples[0], alpha1), alphaFinal );
}

vec4 terrain_mix(vec4[4] samples, float alpha1, float alpha2, float alphaFinal)
{
    return mix( mix(samples[3], samples[2], alpha2), mix(samples[1], samples[0], alpha1), alphaFinal );
}

#if TERRAIN_PLANAR_TEXTURE_SAMPLE_COUNT == 3
// Triplanar mapping

// Pre-transformed texture coordinates for each axial uv slice (Packing: xy, yz, (-x)z, unused)
#define TerrainCoord vec4[2]
// TODO: Decide if we want this threshold
#if 0
#define TERRAIN_TRIPLANAR_MIX_THRESHOLD 0.01
#else // TODO: Remove debug
#define TERRAIN_TRIPLANAR_MIX_THRESHOLD 0.01
#endif

vec4 _t_texture(sampler2D tex, vec2 uv_unflipped, float sign_or_zero)
{
    // Handle case where sign is 0
    float sign = (2.0*sign_or_zero) + 1.0;
    sign /= sign;
    // If the vertex normal is negative, flip the texture back
    // right-side up.
    vec2 uv = uv_unflipped * vec2(sign, 1);
    return texture(tex, uv);
}

#define SAMPLE_X 1 << 2
#define SAMPLE_Y 1 << 1
#define SAMPLE_Z 1 << 0
#define TERRAIN_DEBUG 1 // TODO: Remove debug
struct TerrainWeight
{
    vec3 weight;
    int type;
#if TERRAIN_DEBUG
    vec3 weight_signed;
    vec3 usage;
#endif
};

TerrainWeight _t_weight(TerrainCoord terrain_coord)
{
    float sharpness = TERRAIN_TRIPLANAR_BLEND_FACTOR;
    float threshold = TERRAIN_TRIPLANAR_MIX_THRESHOLD;
    vec3 weight_signed = normalize(pow(abs(vary_vertex_normal), vec3(sharpness)));
    weight_signed -= vec3(threshold);
    TerrainWeight tw;
    tw.weight = max(vec3(0), weight_signed);
    vec3 usage = max(vec3(0), sign(weight_signed));
    tw.type = (int(usage.x) * SAMPLE_X) |
              (int(usage.y) * SAMPLE_Y) |
              (int(usage.z) * SAMPLE_Z);
#if TERRAIN_DEBUG
    tw.weight_signed = weight_signed;
    tw.usage = usage;
#endif
    return tw;
}

struct TerrainSample
{
    vec4 x;
    vec4 y;
    vec4 z;
};

TerrainSample _t_sample(sampler2D tex, TerrainCoord terrain_coord, TerrainWeight tw)
{
    TerrainSample ts;

#if 0
// This demonstrates the case when the bug occurs: Sampling in switch..case
#if 0
#define do_sample_x() _t_texture(tex, terrain_coord[0].zw, sign(vary_vertex_normal.x))
#define do_sample_y() _t_texture(tex, terrain_coord[1].xy, sign(vary_vertex_normal.y))
#else // TODO: Remove debug
// Bug still occurs despite sampling the same texture three times from the same location
#define do_sample_x() _t_texture(tex, terrain_coord[0].xy, sign(vary_vertex_normal.z))
#define do_sample_y() _t_texture(tex, terrain_coord[0].xy, sign(vary_vertex_normal.z))
#endif
#define do_sample_z() _t_texture(tex, terrain_coord[0].xy, sign(vary_vertex_normal.z))
#if 0
    switch (tw.type)
#else // TODO: Remove debug
// Bug still occurs when the type is masked
    switch (tw.type & (SAMPLE_X | SAMPLE_Y | SAMPLE_Z))
#endif
    {
        case (SAMPLE_X | SAMPLE_Y | SAMPLE_Z):
            ts.x = do_sample_x();
            ts.y = do_sample_y();
            ts.z = do_sample_z();
            break;
        case (SAMPLE_X | SAMPLE_Y):
            ts.x = do_sample_x();
            ts.y = do_sample_y();
            ts.z = ts.x;
            break;
        case (SAMPLE_X | SAMPLE_Z):
            ts.x = do_sample_x();
            ts.z = do_sample_z();
            ts.y = ts.x;
            break;
        case (SAMPLE_Y | SAMPLE_Z):
            ts.y = do_sample_y();
            ts.z = do_sample_z();
            ts.x = ts.y;
            break;
        case SAMPLE_X:
            ts.x = do_sample_x();
            ts.y = ts.x;
            ts.z = ts.x;
            break;
        case SAMPLE_Y:
            ts.y = do_sample_y();
            ts.x = ts.y;
            ts.z = ts.y;
            break;
        case SAMPLE_Z:
            ts.z = do_sample_z();
            ts.x = ts.z;
            ts.y = ts.z;
            break;
        default:
            ts.x = vec4(1.0, 0.0, 1.0, 1.0);
            ts.y = ts.x;
            ts.z = ts.x;
            break;
    }
#else // TODO: Remove debug
#if 0
// This demonstrates the case when the bug does not occur: Sampling beforehand and assigning in switch..case
// This otherwise uses the same logic as in the case that reproduces the bug.
#define do_sample_x() _t_texture(tex, terrain_coord[0].zw, sign(vary_vertex_normal.x))
#define do_sample_y() _t_texture(tex, terrain_coord[1].xy, sign(vary_vertex_normal.y))
#define do_sample_z() _t_texture(tex, terrain_coord[0].xy, sign(vary_vertex_normal.z))
    vec4 x = do_sample_x();
    vec4 y = do_sample_y();
    vec4 z = do_sample_z();
    switch (tw.type)
    {
        case (SAMPLE_X | SAMPLE_Y | SAMPLE_Z):
            ts.x = x;
            ts.y = y;
            ts.z = z;
            break;
        case (SAMPLE_X | SAMPLE_Y):
            ts.x = x;
            ts.y = y;
            ts.z = ts.x;
            break;
        case (SAMPLE_X | SAMPLE_Z):
            ts.x = x;
            ts.z = z;
            ts.y = ts.x;
            break;
        case (SAMPLE_Y | SAMPLE_Z):
            ts.y = y;
            ts.z = z;
            ts.x = ts.y;
            break;
        case SAMPLE_X:
            ts.x = x;
            ts.y = ts.x;
            ts.z = ts.x;
            break;
        case SAMPLE_Y:
            ts.y = y;
            ts.x = ts.y;
            ts.z = ts.y;
            break;
        case SAMPLE_Z:
            ts.z = z;
            ts.x = ts.z;
            ts.y = ts.z;
            break;
        default:
            ts.x = vec4(1.0, 0.0, 1.0, 1.0);
            ts.y = ts.x;
            ts.z = ts.x;
            break;
    }
#else // TODO: Keep?
// Test case where the switch..case is broken up into three parts
// This fixes unexplained, "ant trail" seams in terrain. (as seen on Nvidia/Windows 10)
// The extra two branches are not free, but it's still a performance win
// compared to sampling along all three axes for every terrain fragment.
#define do_sample_x() _t_texture(tex, terrain_coord[0].zw, sign(vary_vertex_normal.x))
#define do_sample_y() _t_texture(tex, terrain_coord[1].xy, sign(vary_vertex_normal.y))
#define do_sample_z() _t_texture(tex, terrain_coord[0].xy, sign(vary_vertex_normal.z))
switch (tw.type & SAMPLE_X)
{
    case SAMPLE_X:
        ts.x = do_sample_x();
    break;
    default:
        ts.x = vec4(1.0, 0.0, 1.0, 1.0);
    break;
}
switch (tw.type & SAMPLE_Y)
{
    case SAMPLE_Y:
        ts.y = do_sample_y();
    break;
    default:
        ts.y = vec4(1.0, 0.0, 1.0, 1.0);
    break;
}
switch (tw.type & SAMPLE_Z)
{
    case SAMPLE_Z:
        ts.z = do_sample_z();
    break;
    default:
        ts.z = vec4(1.0, 0.0, 1.0, 1.0);
    break;
}
#endif
#endif

    return ts;
}

struct TerrainSampleNormal
{
    vec3 x;
    vec3 y;
    vec3 z;
};

TerrainSampleNormal _t_sample_n(sampler2D tex, TerrainCoord terrain_coord, TerrainWeight tw)
{
    TerrainSample ts = _t_sample(tex, terrain_coord, tw);
    TerrainSampleNormal tsn;
    tsn.x = ts.x.xyz*2.0-1.0;
    tsn.y = ts.y.xyz*2.0-1.0;
    tsn.z = ts.z.xyz*2.0-1.0;
    vec3 ns = sign(vary_vertex_normal);
    // If the sign is negative, rotate normal by 180 degrees
    tsn.x.xy = (min(0, ns.x) * tsn.x.xy) + (min(0, -ns.x) * -tsn.x.xy);
    tsn.y.xy = (min(0, ns.y) * tsn.y.xy) + (min(0, -ns.y) * -tsn.y.xy);
    tsn.z.xy = (min(0, ns.z) * tsn.z.xy) + (min(0, -ns.z) * -tsn.z.xy);
    // *HACK: Transform normals according to orientation of the UVs
    tsn.x.xy = vec2(-tsn.x.y, tsn.x.x);
    tsn.y.xy = -tsn.y.xy;
    return tsn;
}

TerrainSample _t_sample_c(sampler2D tex, TerrainCoord terrain_coord, TerrainWeight tw)
{
    TerrainSample ts = _t_sample(tex, terrain_coord, tw);
    ts.x.xyz = srgb_to_linear(ts.x.xyz);
    ts.y.xyz = srgb_to_linear(ts.y.xyz);
    ts.z.xyz = srgb_to_linear(ts.z.xyz);
    return ts;
}

// Triplanar sampling of things that are neither colors nor normals (i.e. orm)
vec4 terrain_texture(sampler2D tex, TerrainCoord terrain_coord)
{
    TerrainWeight tw = _t_weight(terrain_coord);

    TerrainSample ts = _t_sample(tex, terrain_coord, tw);

    return ((ts.x * tw.weight.x) + (ts.y * tw.weight.y) + (ts.z * tw.weight.z)) / (tw.weight.x + tw.weight.y + tw.weight.z);
}

// Specialized triplanar normal texture sampling implementation, taking into
// account how the rotation of the texture affects the lighting and trying to
// negate that.
// *TODO: Decide if we want this. It may be better to just calculate the
// tangents on-the-fly here rather than messing with the normals, due to the
// subtleties of the effects of triplanar mapping on UVs. These sampled normals
// are only valid on the faces of a cube.
// *NOTE: Bottom face has not been tested
vec3 terrain_texture_normal(sampler2D tex, TerrainCoord terrain_coord)
{
    TerrainWeight tw = _t_weight(terrain_coord);

    TerrainSampleNormal ts = _t_sample_n(tex, terrain_coord, tw);

    return ((ts.x * tw.weight.x) + (ts.y * tw.weight.y) + (ts.z * tw.weight.z)) / (tw.weight.x + tw.weight.y + tw.weight.z);
}

// Triplanar sampling of colors. Colors are converted to linear space before blending.
vec4 terrain_texture_color(sampler2D tex, TerrainCoord terrain_coord)
{
    TerrainWeight tw = _t_weight(terrain_coord);

    TerrainSample ts = _t_sample_c(tex, terrain_coord, tw);

#if 1
    return ((ts.x * tw.weight.x) + (ts.y * tw.weight.y) + (ts.z * tw.weight.z)) / (tw.weight.x + tw.weight.y + tw.weight.z);
#else // TODO: Remove debug
    //return vec4(vec3(isnan(ts.x)), 1.0);
    //return ts.x;
#if 0
    return vec4(1.0+sign(vary_vertex_normal)/2.0, 1.0);
#else
    return vec4(isnan(tw.weight_signed), 1.0);
#endif
#endif
}

#elif TERRAIN_PLANAR_TEXTURE_SAMPLE_COUNT == 1
#define TerrainCoord vec2
vec4 terrain_texture(sampler2D tex, TerrainCoord terrain_coord)
{
    return texture(tex, terrain_coord);
}

vec3 terrain_texture_normal(sampler2D tex, TerrainCoord terrain_coord)
{
    return texture(tex, terrain_coord).xyz*2.0-1.0;
}

vec4 terrain_texture_color(sampler2D tex, TerrainCoord terrain_coord)
{
    vec4 col = texture(tex, terrain_coord);
    col.xyz = srgb_to_linear(col.xyz);
    return col;
}
#endif

vec3 sample_and_mix_color3(float alpha1, float alpha2, float alphaFinal, TerrainCoord texcoord, vec3[4] factors, sampler2D tex0, sampler2D tex1, sampler2D tex2, sampler2D tex3)
{
    vec3[4] samples;
    samples[0] = terrain_texture(tex0, texcoord).xyz;
    samples[1] = terrain_texture(tex1, texcoord).xyz;
    samples[2] = terrain_texture(tex2, texcoord).xyz;
    samples[3] = terrain_texture(tex3, texcoord).xyz;
    samples[0] = srgb_to_linear(samples[0]);
    samples[1] = srgb_to_linear(samples[1]);
    samples[2] = srgb_to_linear(samples[2]);
    samples[3] = srgb_to_linear(samples[3]);
    samples[0] *= factors[0];
    samples[1] *= factors[1];
    samples[2] *= factors[2];
    samples[3] *= factors[3];
    return terrain_mix(samples, alpha1, alpha2, alphaFinal);
}

vec4 sample_and_mix_color4(float alpha1, float alpha2, float alphaFinal, TerrainCoord texcoord, vec4[4] factors, sampler2D tex0, sampler2D tex1, sampler2D tex2, sampler2D tex3)
{
    vec4[4] samples;
    samples[0] = terrain_texture_color(tex0, texcoord);
    samples[1] = terrain_texture_color(tex1, texcoord);
    samples[2] = terrain_texture_color(tex2, texcoord);
    samples[3] = terrain_texture_color(tex3, texcoord);
    samples[0] *= factors[0];
    samples[1] *= factors[1];
    samples[2] *= factors[2];
    samples[3] *= factors[3];
    return terrain_mix(samples, alpha1, alpha2, alphaFinal);
}

vec3 sample_and_mix_vector3(float alpha1, float alpha2, float alphaFinal, TerrainCoord texcoord, vec3[4] factors, sampler2D tex0, sampler2D tex1, sampler2D tex2, sampler2D tex3)
{
    vec3[4] samples;
    samples[0] = terrain_texture(tex0, texcoord).xyz;
    samples[1] = terrain_texture(tex1, texcoord).xyz;
    samples[2] = terrain_texture(tex2, texcoord).xyz;
    samples[3] = terrain_texture(tex3, texcoord).xyz;
    samples[0] *= factors[0];
    samples[1] *= factors[1];
    samples[2] *= factors[2];
    samples[3] *= factors[3];
    return terrain_mix(samples, alpha1, alpha2, alphaFinal);
}

// Returns the unpacked normal texture in range [-1, 1]
vec3 sample_and_mix_normal(float alpha1, float alpha2, float alphaFinal, TerrainCoord texcoord, sampler2D tex0, sampler2D tex1, sampler2D tex2, sampler2D tex3)
{
    vec3[4] samples;
    samples[0] = terrain_texture_normal(tex0, texcoord).xyz;
    samples[1] = terrain_texture_normal(tex1, texcoord).xyz;
    samples[2] = terrain_texture_normal(tex2, texcoord).xyz;
    samples[3] = terrain_texture_normal(tex3, texcoord).xyz;
    return terrain_mix(samples, alpha1, alpha2, alphaFinal);
}