#version 130
// Fisheye removal for GoPro 11+, 8:7 ratio, without hypersmooth
// Copyright (C) 2025 Jean-Baptiste Berlioz
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program 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 Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

#extension GL_ARB_texture_rectangle: enable

#define rotate_180
//#define debug_borders

#undef highp // defined by Qt-OpenGl
precision highp float;

// uniforms
uniform sampler2DRect myTextureY;
uniform sampler2DRect myTextureU;
uniform sampler2DRect myTextureV;
uniform vec2 myResolution;
uniform float pts;

// parameters
const vec2 sensor_size = vec2(5.949440, 5.205760);
const float equidistant_focal_length = 3.020000;
const float rectilinear_focal_length = 2.232346;

// constants
const int subsampling = 4;
const vec2 subsampling_step = vec2(1.0 / float(subsampling));
const vec2 subsampling_start = subsampling_step * 0.5 - vec2(0.5);
const float subsampling_scale = 1.0 / float(subsampling * subsampling);

// variables
vec2 texture_center;
vec2 texture_to_sensor;
vec2 sensor_to_texture;

void initialize() {
    texture_center = myResolution * 0.5;
    texture_to_sensor = sensor_size / myResolution;
#ifdef rotate_180
    texture_to_sensor *= -1.0;
#endif
    sensor_to_texture = myResolution / sensor_size;
}

vec2 equidistant_to_rectilinear(const in vec2 coord) {
    float rectilinear_radius = length(coord);
    float rectilinear_angle = atan(rectilinear_radius / rectilinear_focal_length);
    float equidistant_radius = rectilinear_angle * equidistant_focal_length;
    return coord * (equidistant_radius / rectilinear_radius);
}

vec4 sample_texture(const in vec2 coord) {
    vec2 rectilinear = equidistant_to_rectilinear((coord - texture_center) * texture_to_sensor);
    vec2 y_coord = texture_center + rectilinear * sensor_to_texture;
#ifdef debug_borders
    if (y_coord.x < 0.0 || y_coord.y < 0.0 || y_coord.x > myResolution.x || y_coord.y > myResolution.y) {
        return vec4(1.0);
    }
#endif
    vec2 uv_coord = y_coord * 0.5;
    return vec4(
        texture2DRect(myTextureY, y_coord).x,
        texture2DRect(myTextureU, uv_coord).x,
        texture2DRect(myTextureV, uv_coord).x,
        1.0);
}

void main() {
    initialize();

    vec2 coord = gl_TexCoord[0].xy;
    vec4 pixel = vec4(0.0);

    for (int y = 0; y < subsampling; y++) {
        for (int x = 0; x < subsampling; x++) {
            vec2 offset = subsampling_start + subsampling_step * vec2(x, y);
            pixel += sample_texture(coord + offset);
        }
    }

    gl_FragColor = pixel * subsampling_scale;
}