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///////////////////////////////////////////////////////////////////////////////////////////////////
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// Copyright 2018 Leszek Koltunski leszek@koltunski.pl //
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// //
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// This file is part of Distorted. //
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// //
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// This library is free software; you can redistribute it and/or //
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// modify it under the terms of the GNU Lesser General Public //
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// License as published by the Free Software Foundation; either //
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// version 2.1 of the License, or (at your option) any later version. //
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// //
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// This library 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 GNU //
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// Lesser General Public License for more details. //
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// //
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// You should have received a copy of the GNU Lesser General Public //
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// License along with this library; if not, write to the Free Software //
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA //
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///////////////////////////////////////////////////////////////////////////////////////////////////
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precision highp float;
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precision highp int;
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out vec4 fragColor; // The output color
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in vec2 v_TexCoordinate; // Interpolated texture coordinate per fragment.
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in vec2 v_Pixel; // location of the current fragment, in pixels
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//////////////////////////////////////////////////////////////////////////////////////////////
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// per-pixel linked list. Order Independent Transparency.
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uniform uvec2 u_Size;
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layout (std430,binding=1) buffer linkedlist // first (u_Size.x*u_Size.y) uints - head pointers,
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{ // one for each pixel in the Output rectangle.
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uint u_Records[]; //
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}; // Next 3*u_numRecords uints - actual linked list, i.e.
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// triplets of (pointer,depth,rgba).
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//////////////////////////////////////////////////////////////////////////////////////////////
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vec4 convert(uint rgba)
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{
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return vec4( float((rgba>>24u)&255u),float((rgba>>16u)&255u),float((rgba>>8u)&255u),float(rgba&255u) ) / 255.0;
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}
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//////////////////////////////////////////////////////////////////////////////////////////////
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// A over B (https://en.wikipedia.org/wiki/Alpha_compositing)
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vec4 blend(vec4 A,vec4 B)
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{
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float b = B.a * (1.0-A.a);
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float a = A.a + b;
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return vec4( (A.rgb*A.a + B.rgb*b)/a , a );
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}
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//////////////////////////////////////////////////////////////////////////////////////////////
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// Pass4 of the OIT algorithm - keep traversing the linked list, build the final color and blend it.
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void main()
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{
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uint prev = uint(v_Pixel.x) + uint(v_Pixel.y) * u_Size.x;
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uint curr = u_Records[prev];
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if (curr != 0u)
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{
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const float S= 2147483647.0;
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gl_FragDepth = 1.0 - 2.0*float(u_Records[curr+1u])/S;
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vec4 color = convert(u_Records[curr+2u]);
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curr = u_Records[curr];
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while (curr != 0u)
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{
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color = blend( color , convert(u_Records[curr+2u]) );
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curr = u_Records[curr];
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}
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fragColor = color;
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}
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else discard;
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}
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