(Shader Library) Electrocardiogram Effect (GLSL)

2011/12/23 JeGX

Here is a cool GLSL effect that simulates an electrocardiogram (ECG). The original effect, in HLSL, comes from the book Hackish C++ Games and Demos (by Michael Flenov). All work is done in the pixel shader.

Here is the complete GLSL program for GeeXLab (easily portable to any other GLSL-based app):

[Vertex_Shader]
#version 120
void main()
{	
  gl_TexCoord[0] = gl_MultiTexCoord0;
  gl_Position = ftransform();
}

[Pixel_Shader]
uniform float time;
float viewAngle = 1.0;
float speed = 3.0;
float rate = 15.0;
float baseamp = 0.10;
void main(void)
{
  vec2 p = -1.0 + 2.0 * gl_TexCoord[0].xy;
  float x = speed * viewAngle * time + rate * p.x;
  float base = (1.0 + cos(x*2.5 + time)) * (1.0 + sin(x*3.5 + time));
  float z = fract(0.05*x);
  z = max(z, 1.0-z);
  z = pow(z, 20.0);
  float pulse = exp(-10000.0 * z);
  vec4 ecg_color = vec4(0.6, 0.7, 0.8, 1.0);
  vec4 c = pow(clamp(1.0-abs(p.y-(baseamp*base+pulse-0.5)), 0.0, 1.0), 16.0) * ecg_color;
  gl_FragColor = c;
}

More shaders are available in the Shader Library.

GLSL live coding in GeeXLab…

The GeeXLab demo is available in the GLSL_Electrocardiogram/ folder of GeeXLab code sample pack:
[download#40#image]

This demo requires GeeXLab 0.3.3+.

How to run the demo: start GeeXLab and drop the demo file (Electrocardiogram.xml) in GeeXLab. That’s all.