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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;
++
++ void MAIN()
++ {
++ POSITION = MODELVIEWPROJECTION_MATRIX * vec4(VERTEX, 1.0);
++ transformed_eye = (inverse(MODEL_MATRIX) * vec4(CAMERA_POSITION, 1.0)).xyz / 100 + vec3(0.5);
++ vray_dir = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz - CAMERA_POSITION;
++ }