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// Adapted from https://github.com/Twinklebear/webgl-volume-raycaster
//
// The MIT License (MIT)
// Copyright (c) 2018 Will Usher
// 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.
VARYING vec3 vray_dir;
VARYING vec3 transformed_eye;
vec2 intersect_box(vec3 orig, vec3 dir)
{
const vec3 box_min = vec3(0);
const vec3 box_max = vec3(1);
vec3 inv_dir = 1.0 / dir;
vec3 tmin_tmp = (box_min - orig) * inv_dir;
vec3 tmax_tmp = (box_max - orig) * inv_dir;
vec3 tmin = min(tmin_tmp, tmax_tmp);
vec3 tmax = max(tmin_tmp, tmax_tmp);
float t0 = max(tmin.x, max(tmin.y, tmin.z));
float t1 = min(tmax.x, min(tmax.y, tmax.z));
return vec2(t0, t1);
}
void MAIN()
{
const vec3 volume_dims = vec3(256, 256, 256);
vec3 ray_dir = normalize(vray_dir);
vec2 t_hit = intersect_box(transformed_eye, ray_dir);
if (t_hit.x > t_hit.y)
discard;
vec3 dt_vec = 1.0 / (vec3(volume_dims) * abs(ray_dir));
float dt = min(dt_vec.x, min(dt_vec.y, dt_vec.z));
float offset = 0;
vec3 p = transformed_eye + (t_hit.x + offset * dt) * ray_dir;
const float dt_scale = 1.0;
FRAGCOLOR = vec4(0);
for (float t = t_hit.x; t < t_hit.y; t += dt) {
// Use textureLod, to play nice with HLSL
float val = textureLod(volume, vec3(p.x, p.y, p.z), 0).r;
vec4 val_color = vec4(textureLod(colormap, vec2(val, 0.5), 0).rgb, val);
// Opacity correction
val_color.a = 1.0 - pow(max(0.0, 1.0 - val_color.a), dt_scale);
FRAGCOLOR.rgb += (1.0 - FRAGCOLOR.a) * val_color.a * val_color.rgb;
FRAGCOLOR.a += (1.0 - FRAGCOLOR.a) * val_color.a;
if (FRAGCOLOR.a >= 0.95)
break;
p += ray_dir * dt;
}
}
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