libigl/tutorial/114_CustomShader/main.cpp

#include <igl/read_triangle_mesh.h>
#include <igl/opengl/glfw/Viewer.h>
#include <igl/opengl/create_shader_program.h>
#include <igl/opengl/destroy_shader_program.h>
#include <Eigen/Core>

int main(int argc, char *argv[])
{
  using namespace Eigen;
  using namespace std;
  Eigen::MatrixXd V;
  Eigen::MatrixXi F;
  igl::opengl::glfw::Viewer v;
  igl::read_triangle_mesh(
    argc>1?argv[1]: TUTORIAL_SHARED_PATH "/bunny.off", V, F);
  v.data().set_mesh(V,F);
  v.data().set_face_based(false);
  v.data().show_lines = false;
  v.launch_init();

  v.data().meshgl.init();
  igl::opengl::destroy_shader_program(v.data().meshgl.shader_mesh);

  // Custom shader that adds a Fresnel effect
  {
    std::string mesh_vertex_shader_string =
R"(#version 150
uniform mat4 view;
uniform mat4 proj;
uniform mat4 normal_matrix;
in vec3 position;
in vec3 normal;
out vec3 position_eye;
out vec3 normal_eye;
in vec4 Ka;
in vec4 Kd;
in vec4 Ks;
in vec2 texcoord;
out vec2 texcoordi;
out vec4 Kai;
out vec4 Kdi;
out vec4 Ksi;

void main()
{
  position_eye = vec3 (view * vec4 (position, 1.0));
  normal_eye = vec3 (normal_matrix * vec4 (normal, 0.0));
  normal_eye = normalize(normal_eye);
  gl_Position = proj * vec4 (position_eye, 1.0); //proj * view * vec4(position, 1.0);
  Kai = Ka;
  Kdi = Kd;
  Ksi = Ks;
  texcoordi = texcoord;
})";

    std::string mesh_fragment_shader_string =
R"(#version 150
uniform mat4 view;
uniform mat4 proj;
uniform vec4 fixed_color;
in vec3 position_eye;
in vec3 normal_eye;
uniform vec3 light_position_eye;
vec3 Ls = vec3 (1, 1, 1);
vec3 Ld = vec3 (1, 1, 1);
vec3 La = vec3 (1, 1, 1);
in vec4 Ksi;
in vec4 Kdi;
in vec4 Kai;
in vec2 texcoordi;
uniform sampler2D tex;
uniform float specular_exponent;
uniform float lighting_factor;
uniform float texture_factor;
out vec4 outColor;
void main()
{
vec3 Ia = La * vec3(Kai);    // ambient intensity

vec3 vector_to_light_eye = light_position_eye - position_eye;
vec3 direction_to_light_eye = normalize (vector_to_light_eye);
float dot_prod = dot (direction_to_light_eye, normalize(normal_eye));
float clamped_dot_prod = max (dot_prod, 0.0);
vec3 Id = Ld * vec3(Kdi) * clamped_dot_prod;    // Diffuse intensity

vec3 reflection_eye = reflect (-direction_to_light_eye, normalize(normal_eye));
vec3 surface_to_viewer_eye = normalize (-position_eye);
float dot_prod_specular = dot (reflection_eye, surface_to_viewer_eye);
dot_prod_specular = float(abs(dot_prod)==dot_prod) * max (dot_prod_specular, 0.0);
float specular_factor = pow (dot_prod_specular, specular_exponent);
vec3 Kfi = 0.5*vec3(Ksi);
vec3 Lf = Ls;
float fresnel_exponent = 2*specular_exponent;
float fresnel_factor = 0;
{
  float NE = max( 0., dot( normalize(normal_eye), surface_to_viewer_eye));
  fresnel_factor = pow (max(sqrt(1. - NE*NE),0.0), fresnel_exponent);
}
vec3 Is = Ls * vec3(Ksi) * specular_factor;    // specular intensity
vec3 If = Lf * vec3(Kfi) * fresnel_factor;     // fresnel intensity
vec4 color = vec4(lighting_factor * (If + Is + Id) + Ia +
  (1.0-lighting_factor) * vec3(Kdi),(Kai.a+Ksi.a+Kdi.a)/3);
outColor = mix(vec4(1,1,1,1), texture(tex, texcoordi), texture_factor) * color;
if (fixed_color != vec4(0.0)) outColor = fixed_color;
})";

    igl::opengl::create_shader_program(
      mesh_vertex_shader_string,
      mesh_fragment_shader_string,
      {},
      v.data().meshgl.shader_mesh);
  }

  v.launch_rendering(true);
  v.launch_shut();
}