RtB/data/shaders/default_fs.glsl

#version 120
// uniform data
uniform sampler2D texture_sampler;
// in
varying vec2 frag_uv;

void main() {
  //gl_FragColor = texture2D(texture_sampler, frag_uv);
  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}