text: var vertex_shader_src = 'varying vec3 vertex;\nvoid main() {\nvertex = vec3(position.x * 3.0, position.y * 6.0, position.z * 3.0);\ngl_Position = projectionMatrix * modelViewMatrix * vec4(position.xyz, 1.0);\n}';
  var grid_fragment_src = '#extension GL_OES_standard_derivatives : enable\nvarying vec3 vertex;\nvoid main() {\nvec2 coord = vertex.xz;\nvec2 grid = abs(fract(coord - 0.5) - 0.5) / fwidth(coord);\nfloat line = min(grid.x, grid.y);\ngl_FragColor = vec4(vec3(1.0 - min(line, 1.0)) * vec3(0.0, 0.2, 0.22), 1.0);\n}';
  