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7f1735dc
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Leszek Koltunski
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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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7170e4eb
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leszek
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Leszek Koltunski
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precision highp float;
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precision highp int;
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leszek
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out vec4 fragColor;
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in vec2 v_TexCoordinate;
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Leszek Koltunski
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in vec2 v_Pixel; // location of the current fragment, in pixels
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uniform sampler2D u_Texture;
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uniform sampler2D u_DepthTexture;
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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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uniform uint u_numRecords;
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layout (binding=0, offset=0) uniform atomic_uint u_Counter;
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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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// Concurrent insert to a linked list. Tim Harris, 'pragmatic implementation of non-blocking
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// linked-lists', 2001.
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// This arranges fragments by decreasing 'depth', so one would think - from back to front, but
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// in main() below the depth is mapped with S*(1-depth)/2, so it is really front to back.
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void insert( vec2 ij, uint depth, uint rgba )
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{
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uint ptr = atomicCounterIncrement(u_Counter);
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if( ptr<u_numRecords )
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{
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ptr = 3u*ptr + u_Size.x*u_Size.y;
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u_Records[ptr+1u] = depth;
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u_Records[ptr+2u] = rgba;
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memoryBarrier();
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uint prev = uint(ij.x) + uint(ij.y) * u_Size.x;
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uint curr = u_Records[prev];
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while (true)
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{
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if ( curr==0u || depth > u_Records[curr+1u] ) // need to insert here
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{
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u_Records[ptr] = curr; // next of new record is curr
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memoryBarrier();
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uint res = atomicCompSwap( u_Records[prev], curr, ptr );
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if (res==curr) break; // done!
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else curr = res; // could not insert! retry from same place in list
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}
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else // advance in list
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{
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prev = curr;
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curr = u_Records[prev];
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}
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}
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}
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}
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//////////////////////////////////////////////////////////////////////////////////////////////
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uint convert(vec4 c)
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{
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return ((uint(255.0*c.r))<<24u) + ((uint(255.0*c.g))<<16u) + ((uint(255.0*c.b))<<8u) + uint(255.0*c.a);
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}
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//////////////////////////////////////////////////////////////////////////////////////////////
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// Pass2 of the OIT algorithm - build the LinkedList phase.
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void main()
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{
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vec4 color= texture(u_Texture , v_TexCoordinate);
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float depth= texture(u_DepthTexture, v_TexCoordinate).r;
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if( color.a > 0.97 )
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{
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gl_FragDepth = depth;
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fragColor = color;
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}
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else
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{
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if( color.a > 0.0 )
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{
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const float S= 2147483647.0; // max signed int. Could probably be max unsigned int but this is enough.
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insert(v_Pixel, uint(S*(1.0-depth)/2.0), convert(color) );
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}
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discard;
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}
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7170e4eb
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leszek
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}
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