76 lines
2.6 KiB
Plaintext
76 lines
2.6 KiB
Plaintext
/*
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oolite-dust.vertex
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Vertex shader for interplanetary dust.
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© 2010-2013 Jens Ayton
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA.
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*/
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/* The following macros are provided by Oolite, to ensure that they stay in
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sync with the values used in non-shader mode.
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#define OODUST_SCALE_MAX (float(2))
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#define OODUST_SCALE_FACTOR (float(0.002))
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#define OODUST_SIZE (float(2000))
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*/
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/* “Warpiness”: 0 for dots when not warping and the near end of lines when
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warping, 1 for the far end of lines when warping. (Note that both “ends”
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have the same input coordinates, and the shader applies the warp effect.)
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*/
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attribute float aWarpiness;
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uniform vec4 uWarp;
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// Player position, offset by -OODUST_SIZE/2 on each coordinate.
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uniform vec4 uOffsetPlayerPosition;
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varying vec4 vColor;
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uniform mat4 ooliteModelViewProjection;
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void main(void)
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{
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/* Dust particles are arranged in a cube of 2000×2000×2000 metres
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(OO_DUST_SIZE) around the universe origin. The following code offsets
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each particle to be somewhere in a cube of the same size around the
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player, creating an infinite repeating pattern.
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*/
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vec4 position = mod(gl_Vertex - uOffsetPlayerPosition, OODUST_SIZE) + uOffsetPlayerPosition;
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position = position - uWarp * aWarpiness;
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// Project the dust, and find its distance from the camera.
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position.w = 1.0;
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position = ooliteModelViewProjection * position;
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gl_Position = position;
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float distance = length(position);
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/* The original non-shader code fades to black using linear fog, with a
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near plane of 500 and a far plane of 1000.
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OODUST_SCALE_MAX is far plane/near plane, and OODUST_SCALE_FACTOR
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is 1.0/(far plane - near plane).
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This gives us a function such that f(x) ≥ 1 when x ≤ near plane,
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f(x) ≤ 0 when x ≥ far plane, and a linear ramp in between, which we
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then clamp to [0..1].
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*/
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float alpha = clamp(OODUST_SCALE_MAX - distance * OODUST_SCALE_FACTOR, 0.0, 1.0);
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vColor = vec4(gl_Color.rgb, alpha * gl_Color.a);
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}
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