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141 lines
3.9 KiB
Plaintext
141 lines
3.9 KiB
Plaintext
/*
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This file is part of Caelum.
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See http://www.ogre3d.org/wiki/index.php/Caelum
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Copyright (c) 2006-2007 Caelum team. See Contributors.txt for details.
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Caelum is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Caelum 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 Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with Caelum. If not, see <http://www.gnu.org/licenses/>.
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*/
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// Returns (exp(x) - 1) / x; avoiding division by 0.
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// lim when x -> 0 is 1.
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float expdiv(float x) {
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if (abs(x) < 0.0001) {
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return 1;
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} else {
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return (exp(x) - 1) / x;
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}
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}
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// Return fogging through a layer of fog which drops exponentially by height.
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//
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// Standard exp fog with constant density would return (1 - exp(-density * dist)).
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// This function assumes a variable density vd = exp(-verticalDecay * h - baseLevel)
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// Full computation is exp(density * dist / (h2 - h1) * int(h1, h2, exp(-verticalDecay * (h2 - h1)))).
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//
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// This will gracefully degrade to standard exp fog in verticalDecay is 0; without throwing NaNs.
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float ExpGroundFog (
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float dist, float h1, float h2,
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float density, float verticalDecay, float baseLevel)
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{
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float deltaH = (h2 - h1);
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return 1 - exp (-density * dist * exp(verticalDecay * (baseLevel - h1)) * expdiv(-verticalDecay * deltaH));
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}
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// Just like ExpGroundFog with h2 = positive infinity
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// When h2 == negative infinity the value is always +1.
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float ExpGroundFogInf (
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float invSinView, float h1,
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float density, float verticalDecay, float baseLevel)
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{
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return 1 - exp (-density * invSinView * exp(verticalDecay * (baseLevel - h1)) * (1 / verticalDecay));
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}
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// Entry point for GroundFog vertex program.
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void GroundFog_vp
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(
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float4 position : POSITION,
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out float4 oPosition : POSITION,
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out float4 worldPos : TEXCOORD0,
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uniform float4x4 worldViewProj,
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uniform float4x4 world
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) {
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oPosition = mul(worldViewProj, position);
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worldPos = mul(world, position);
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}
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// Entry point for GroundFog fragment program.
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void GroundFog_fp
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(
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in float3 worldPos : TEXCOORD0,
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uniform float3 camPos,
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uniform float4 fogColour,
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uniform float fogDensity,
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uniform float fogVerticalDecay,
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uniform float fogGroundLevel,
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out float4 oCol : COLOR
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) {
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float h1 = camPos.y;
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float h2 = worldPos.y;
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float dist = length(camPos - worldPos);
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float fog = ExpGroundFog(
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dist, h1, h2,
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fogDensity, fogVerticalDecay, fogGroundLevel);
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oCol.rgb = fogColour.rgb;
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oCol.a = fog;
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}
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// Entry point for GroundFogDome vertex program.
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void GroundFogDome_vp
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(
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in float4 position : POSITION,
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out float4 oPosition : POSITION,
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out float3 relPosition : TEXCOORD0,
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uniform float4x4 worldViewProj
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) {
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oPosition = mul(worldViewProj, position);
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relPosition = normalize(position.xyz);
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}
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// Entry point for the GroundFogDome fragment program.
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void GroundFogDome_fp
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(
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in float3 relPosition : TEXCOORD0,
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uniform float cameraHeight,
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uniform float4 fogColour,
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uniform float fogDensity,
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uniform float fogVerticalDecay,
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uniform float fogGroundLevel,
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out float4 oCol : COLOR
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) {
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// Fog magic.
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float invSinView = 1 / (relPosition.y);
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float h1 = cameraHeight;
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float aFog;
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if (fogVerticalDecay < 1e-7) {
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// A value of zero of fogVerticalDecay would result in maximum (1) aFog everywhere.
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// Output 0 zero instead to disable.
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aFog = 0;
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} else {
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if (invSinView < 0) {
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// Gazing into the abyss
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aFog = 1;
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} else {
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aFog = saturate (ExpGroundFogInf (
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invSinView, h1,
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fogDensity, fogVerticalDecay, fogGroundLevel));
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}
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}
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oCol.a = aFog;
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oCol.rgb = fogColour.rgb;
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} |