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// ============================================================================
//
// Program: Visualization Toolkit
// Module: vtkSobelGradientMagnitudePassShader2_fs.glsl
//
// Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
// All rights reserved.
// See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
//
// This software is distributed WITHOUT ANY WARRANTY; without even
// the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
// PURPOSE. See the above copyright notice for more information.
//
// ============================================================================
// Fragment shader used by the second pass of the Sobel filter render pass.
#version 110
uniform sampler2D gx1;
uniform sampler2D gy1;
uniform float stepSize; // 1/H
void main(void)
{
vec2 tcoord=gl_TexCoord[0].st;
vec2 offset=vec2(0.0,stepSize);
// Gx
vec4 tx1=texture2D(gx1,tcoord-offset);
vec4 tx2=texture2D(gx1,tcoord);
vec4 tx3=texture2D(gx1,tcoord+offset);
// if clamped textures, rescale values from [0,1] to [-1,1]
tx1=tx1*2.0-1.0;
tx2=tx2*2.0-1.0;
tx3=tx3*2.0-1.0;
vec4 gx=(tx1+2.0*tx2+tx3)/4.0;
// Gy
vec4 ty1=texture2D(gy1,tcoord-offset);
vec4 ty3=texture2D(gy1,tcoord+offset);
vec4 gy=ty3-ty1;
// the maximum gradient magnitude is sqrt(2.0) when for example gx=1 and
// gy=1
// gl_FragColor=sqrt((gx*gx+gy*gy)/2.0);
gl_FragColor.rgb=sqrt((gx.rgb*gx.rgb+gy.rgb*gy.rgb)/2.0);
gl_FragColor.a=1.0; // arbitrary choice.
}
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