A simple fragment shader example
Consider a complete example of using the fragment shader in an openFrameworks project. It will be a base for other fragment shaders' examples. The shader here is pretty simple. It just inverts the colors of all the drawn pixels.
Note
This is example 08-Shaders/01-ShaderInverting.
This example is based on the emptyExample project in openFrameworks.
Creating the fragment shader
In the bin/data folder, create a new text file shaderFrag.c that contains the fragment shader's code as follows:
#version 120
#extension GL_ARB_texture_rectangle : enable
#extension GL_EXT_gpu_shader4 : enable
uniform sampler2DRect texture0;
void main(){
//Getting coordinates of the current pixel in texture
vec2 pos = gl_TexCoord[0].xy;
//Getting the pixel color from the texture texture0 in pos
vec4 color = texture2DRect(texture0, pos);
//Changing the color - invert red, green, blue components
color.r = 1.0 - color.r;
color.g = 1.0 - color.g;
color.b = 1.0 - color.b;
...
