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// ============================================================================
//
// Program: Visualization Toolkit
// Module: vtkSobelGradientMagnitudePassShader1_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 first pass of the Sobel filter render pass.
#version 110
// GLSL Spec 1.10 rev 59 30-April-2004 defines gl_FragData[] but implementation
// older than the spec only has it as an extension
// (nVidia Linux driver 100.14.13, OpenGL version 2.1.1,
// on Quadro FX 3500/PCI/SSE2)
#extension GL_ARB_draw_buffers : enable
uniform sampler2D source;
uniform float stepSize; // 1/W
void main(void)
{
vec2 tcoord=gl_TexCoord[0].st;
vec2 offset=vec2(stepSize,0.0);
vec4 t1=texture2D(source,tcoord-offset);
vec4 t2=texture2D(source,tcoord);
vec4 t3=texture2D(source,tcoord+offset);
// Gx
// version with unclamped float textures t3-t1 will be in [-1,1]
// gl_FragData[0]=t3-t1;
// version with clamped unchar textures (t3-t1+1)/2 stays in [0,1]
gl_FragData[0]=(t3-t1+1.0)/2.0;
// Gy
gl_FragData[1]=(t1+2.0*t2+t3)/4.0;
}
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