#version 100
precision mediump float;
// The inputs from the vertex shader
// - color of the vertex
// - texture coordinates
varying vec4 v_color;
varying vec2 v_texCoords;
// The texture used for the object
// It is a constant (uniform) accross all vertices.
uniform sampler2D u_texture;
// The main program starts here.

#extension GL_OES_standard_derivatives : enable

void main(void) {
  // Compute the color from the texture and texture coordinates
  vec4 color = texture2D(u_texture, v_texCoords);

  vec2 coord = v_texCoords.xy;

  // Compute anti-aliased world-space grid lines
  vec2 grid = abs(fract(coord - 0.5) - 0.5) / fwidth(coord);
  float line = min(grid.x, grid.y);

  // Just visualize the grid lines directly
  gl_FragColor = vec4(vec3(1.0 - min(line, 1.0)), 1.0);

  // Compute the final color by multiplying with the color of the object
  //gl_FragColor = color * v_color;
}