examples/heightmap.c - third_party/glfw - Git at Google

 //========================================================================
 // Heightmap example program using OpenGL 3 core profile
 // Copyright (c) 2010 Olivier Delannoy
 //
 // This software is provided 'as-is', without any express or implied
 // warranty. In no event will the authors be held liable for any damages
 // arising from the use of this software.
 //
 // Permission is granted to anyone to use this software for any purpose,
 // including commercial applications, and to alter it and redistribute it
 // freely, subject to the following restrictions:
 //
 // 1. The origin of this software must not be misrepresented; you must not
 //    claim that you wrote the original software. If you use this software
 //    in a product, an acknowledgment in the product documentation would
 //    be appreciated but is not required.
 //
 // 2. Altered source versions must be plainly marked as such, and must not
 //    be misrepresented as being the original software.
 //
 // 3. This notice may not be removed or altered from any source
 //    distribution.
 //
 //========================================================================

 #include <stdlib.h>
 #include <stdio.h>
 #include <math.h>
 #include <assert.h>
 #include <stddef.h>

 #define GLAD_GL_IMPLEMENTATION
 #include <glad/gl.h>
 #define GLFW_INCLUDE_NONE
 #include <GLFW/glfw3.h>

 /* Map height updates */
 #define MAX_CIRCLE_SIZE (5.0f)
 #define MAX_DISPLACEMENT (1.0f)
 #define DISPLACEMENT_SIGN_LIMIT (0.3f)
 #define MAX_ITER (200)
 #define NUM_ITER_AT_A_TIME (1)

 /* Map general information */
 #define MAP_SIZE (10.0f)
 #define MAP_NUM_VERTICES (80)
 #define MAP_NUM_TOTAL_VERTICES (MAP_NUM_VERTICES*MAP_NUM_VERTICES)
 #define MAP_NUM_LINES (3* (MAP_NUM_VERTICES - 1) * (MAP_NUM_VERTICES - 1) + \
                2 * (MAP_NUM_VERTICES - 1))


 /**********************************************************************
  * Default shader programs
  *********************************************************************/

 static const char* vertex_shader_text =
 "#version 150\n"
 "uniform mat4 project;\n"
 "uniform mat4 modelview;\n"
 "in float x;\n"
 "in float y;\n"
 "in float z;\n"
 "\n"
 "void main()\n"
 "{\n"
 "   gl_Position = project * modelview * vec4(x, y, z, 1.0);\n"
 "}\n";

 static const char* fragment_shader_text =
 "#version 150\n"
 "out vec4 color;\n"
 "void main()\n"
 "{\n"
 "    color = vec4(0.2, 1.0, 0.2, 1.0); \n"
 "}\n";

 /**********************************************************************
  * Values for shader uniforms
  *********************************************************************/

 /* Frustum configuration */
 static GLfloat view_angle = 45.0f;
 static GLfloat aspect_ratio = 4.0f/3.0f;
 static GLfloat z_near = 1.0f;
 static GLfloat z_far = 100.f;

 /* Projection matrix */
 static GLfloat projection_matrix[16] = {
     1.0f, 0.0f, 0.0f, 0.0f,
     0.0f, 1.0f, 0.0f, 0.0f,
     0.0f, 0.0f, 1.0f, 0.0f,
     0.0f, 0.0f, 0.0f, 1.0f
 };

 /* Model view matrix */
 static GLfloat modelview_matrix[16] = {
     1.0f, 0.0f, 0.0f, 0.0f,
     0.0f, 1.0f, 0.0f, 0.0f,
     0.0f, 0.0f, 1.0f, 0.0f,
     0.0f, 0.0f, 0.0f, 1.0f
 };

 /**********************************************************************
  * Heightmap vertex and index data
  *********************************************************************/

 static GLfloat map_vertices[3][MAP_NUM_TOTAL_VERTICES];
 static GLuint  map_line_indices[2*MAP_NUM_LINES];

 /* Store uniform location for the shaders
  * Those values are setup as part of the process of creating
  * the shader program. They should not be used before creating
  * the program.
  */
 static GLuint mesh;
 static GLuint mesh_vbo[4];

 /**********************************************************************
  * OpenGL helper functions
  *********************************************************************/

 /* Creates a shader object of the specified type using the specified text
  */
 static GLuint make_shader(GLenum type, const char* text)
 {
     GLuint shader;
     GLint shader_ok;
     GLsizei log_length;
     char info_log[8192];

     shader = glCreateShader(type);
     if (shader != 0)
     {
         glShaderSource(shader, 1, (const GLchar**)&text, NULL);
         glCompileShader(shader);
         glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_ok);
         if (shader_ok != GL_TRUE)
         {
             fprintf(stderr, "ERROR: Failed to compile %s shader\n", (type == GL_FRAGMENT_SHADER) ? "fragment" : "vertex" );
             glGetShaderInfoLog(shader, 8192, &log_length,info_log);
             fprintf(stderr, "ERROR: \n%s\n\n", info_log);
             glDeleteShader(shader);
             shader = 0;
         }
     }
     return shader;
 }

 /* Creates a program object using the specified vertex and fragment text
  */
 static GLuint make_shader_program(const char* vs_text, const char* fs_text)
 {
     GLuint program = 0u;
     GLint program_ok;
     GLuint vertex_shader = 0u;
     GLuint fragment_shader = 0u;
     GLsizei log_length;
     char info_log[8192];

     vertex_shader = make_shader(GL_VERTEX_SHADER, vs_text);
     if (vertex_shader != 0u)
     {
         fragment_shader = make_shader(GL_FRAGMENT_SHADER, fs_text);
         if (fragment_shader != 0u)
         {
             /* make the program that connect the two shader and link it */
             program = glCreateProgram();
             if (program != 0u)
             {
                 /* attach both shader and link */
                 glAttachShader(program, vertex_shader);
                 glAttachShader(program, fragment_shader);
                 glLinkProgram(program);
                 glGetProgramiv(program, GL_LINK_STATUS, &program_ok);

                 if (program_ok != GL_TRUE)
                 {
                     fprintf(stderr, "ERROR, failed to link shader program\n");
                     glGetProgramInfoLog(program, 8192, &log_length, info_log);
                     fprintf(stderr, "ERROR: \n%s\n\n", info_log);
                     glDeleteProgram(program);
                     glDeleteShader(fragment_shader);
                     glDeleteShader(vertex_shader);
                     program = 0u;
                 }
             }
         }
         else
         {
             fprintf(stderr, "ERROR: Unable to load fragment shader\n");
             glDeleteShader(vertex_shader);
         }
     }
     else
     {
         fprintf(stderr, "ERROR: Unable to load vertex shader\n");
     }
     return program;
 }

 /**********************************************************************
  * Geometry creation functions
  *********************************************************************/

 /* Generate vertices and indices for the heightmap
  */
 static void init_map(void)
 {
     int i;
     int j;
     int k;
     GLfloat step = MAP_SIZE / (MAP_NUM_VERTICES - 1);
     GLfloat x = 0.0f;
     GLfloat z = 0.0f;
     /* Create a flat grid */
     k = 0;
     for (i = 0 ; i < MAP_NUM_VERTICES ; ++i)
     {
         for (j = 0 ; j < MAP_NUM_VERTICES ; ++j)
         {
             map_vertices[0][k] = x;
             map_vertices[1][k] = 0.0f;
             map_vertices[2][k] = z;
             z += step;
             ++k;
         }
         x += step;
         z = 0.0f;
     }
 #if DEBUG_ENABLED
     for (i = 0 ; i < MAP_NUM_TOTAL_VERTICES ; ++i)
     {
         printf ("Vertice %d (%f, %f, %f)\n",
                 i, map_vertices[0][i], map_vertices[1][i], map_vertices[2][i]);

     }
 #endif
     /* create indices */
     /* line fan based on i
      * i+1
      * |  / i + n + 1
      * | /
      * |/
      * i --- i + n
      */

     /* close the top of the square */
     k = 0;
     for (i = 0 ; i < MAP_NUM_VERTICES  -1 ; ++i)
     {
         map_line_indices[k++] = (i + 1) * MAP_NUM_VERTICES -1;
         map_line_indices[k++] = (i + 2) * MAP_NUM_VERTICES -1;
     }
     /* close the right of the square */
     for (i = 0 ; i < MAP_NUM_VERTICES -1 ; ++i)
     {
         map_line_indices[k++] = (MAP_NUM_VERTICES - 1) * MAP_NUM_VERTICES + i;
         map_line_indices[k++] = (MAP_NUM_VERTICES - 1) * MAP_NUM_VERTICES + i + 1;
     }

     for (i = 0 ; i < (MAP_NUM_VERTICES - 1) ; ++i)
     {
         for (j = 0 ; j < (MAP_NUM_VERTICES - 1) ; ++j)
         {
             int ref = i * (MAP_NUM_VERTICES) + j;
             map_line_indices[k++] = ref;
             map_line_indices[k++] = ref + 1;

             map_line_indices[k++] = ref;
             map_line_indices[k++] = ref + MAP_NUM_VERTICES;

             map_line_indices[k++] = ref;
             map_line_indices[k++] = ref + MAP_NUM_VERTICES + 1;
         }
     }

 #ifdef DEBUG_ENABLED
     for (k = 0 ; k < 2 * MAP_NUM_LINES ; k += 2)
     {
         int beg, end;
         beg = map_line_indices[k];
         end = map_line_indices[k+1];
         printf ("Line %d: %d -> %d (%f, %f, %f) -> (%f, %f, %f)\n",
                 k / 2, beg, end,
                 map_vertices[0][beg], map_vertices[1][beg], map_vertices[2][beg],
                 map_vertices[0][end], map_vertices[1][end], map_vertices[2][end]);
     }
 #endif
 }

 static void generate_heightmap__circle(float* center_x, float* center_y,
         float* size, float* displacement)
 {
     float sign;
     /* random value for element in between [0-1.0] */
     *center_x = (MAP_SIZE * rand()) / (float) RAND_MAX;
     *center_y = (MAP_SIZE * rand()) / (float) RAND_MAX;
     *size = (MAX_CIRCLE_SIZE * rand()) / (float) RAND_MAX;
     sign = (1.0f * rand()) / (float) RAND_MAX;
     sign = (sign < DISPLACEMENT_SIGN_LIMIT) ? -1.0f : 1.0f;
     *displacement = (sign * (MAX_DISPLACEMENT * rand())) / (float) RAND_MAX;
 }

 /* Run the specified number of iterations of the generation process for the
  * heightmap
  */
 static void update_map(int num_iter)
 {
     assert(num_iter > 0);
     while(num_iter)
     {
         /* center of the circle */
         float center_x;
         float center_z;
         float circle_size;
         float disp;
         size_t ii;
         generate_heightmap__circle(&center_x, &center_z, &circle_size, &disp);
         disp = disp / 2.0f;
         for (ii = 0u ; ii < MAP_NUM_TOTAL_VERTICES ; ++ii)
         {
             GLfloat dx = center_x - map_vertices[0][ii];
             GLfloat dz = center_z - map_vertices[2][ii];
             GLfloat pd = (2.0f * (float) sqrt((dx * dx) + (dz * dz))) / circle_size;
             if (fabs(pd) <= 1.0f)
             {
                 /* tx,tz is within the circle */
                 GLfloat new_height = disp + (float) (cos(pd*3.14f)*disp);
                 map_vertices[1][ii] += new_height;
             }
         }
         --num_iter;
     }
 }

 /**********************************************************************
  * OpenGL helper functions
  *********************************************************************/

 /* Create VBO, IBO and VAO objects for the heightmap geometry and bind them to
  * the specified program object
  */
 static void make_mesh(GLuint program)
 {
     GLuint attrloc;

     glGenVertexArrays(1, &mesh);
     glGenBuffers(4, mesh_vbo);
     glBindVertexArray(mesh);
     /* Prepare the data for drawing through a buffer inidices */
     glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mesh_vbo[3]);
     glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint)* MAP_NUM_LINES * 2, map_line_indices, GL_STATIC_DRAW);

     /* Prepare the attributes for rendering */
     attrloc = glGetAttribLocation(program, "x");
     glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[0]);
     glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[0][0], GL_STATIC_DRAW);
     glEnableVertexAttribArray(attrloc);
     glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);

     attrloc = glGetAttribLocation(program, "z");
     glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[2]);
     glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[2][0], GL_STATIC_DRAW);
     glEnableVertexAttribArray(attrloc);
     glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);

     attrloc = glGetAttribLocation(program, "y");
     glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[1]);
     glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[1][0], GL_DYNAMIC_DRAW);
     glEnableVertexAttribArray(attrloc);
     glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);
 }

 /* Update VBO vertices from source data
  */
 static void update_mesh(void)
 {
     glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[1][0]);
 }

 /**********************************************************************
  * GLFW callback functions
  *********************************************************************/

 static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
 {
     switch(key)
     {
         case GLFW_KEY_ESCAPE:
             /* Exit program on Escape */
             glfwSetWindowShouldClose(window, GLFW_TRUE);
             break;
     }
 }

 static void error_callback(int error, const char* description)
 {
     fprintf(stderr, "Error: %s\n", description);
 }

 int main(int argc, char** argv)
 {
     GLFWwindow* window;
     int iter;
     double dt;
     double last_update_time;
     int frame;
     float f;
     GLint uloc_modelview;
     GLint uloc_project;
     int width, height;

     GLuint shader_program;

     glfwSetErrorCallback(error_callback);

     if (!glfwInit())
         exit(EXIT_FAILURE);

     glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
     glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
     glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);

     window = glfwCreateWindow(800, 600, "GLFW OpenGL3 Heightmap demo", NULL, NULL);
     if (! window )
     {
         glfwTerminate();
         exit(EXIT_FAILURE);
     }

     /* Register events callback */
     glfwSetKeyCallback(window, key_callback);

     glfwMakeContextCurrent(window);
     gladLoadGL(glfwGetProcAddress);

     /* Prepare opengl resources for rendering */
     shader_program = make_shader_program(vertex_shader_text, fragment_shader_text);

     if (shader_program == 0u)
     {
         glfwTerminate();
         exit(EXIT_FAILURE);
     }

     glUseProgram(shader_program);
     uloc_project   = glGetUniformLocation(shader_program, "project");
     uloc_modelview = glGetUniformLocation(shader_program, "modelview");

     /* Compute the projection matrix */
     f = 1.0f / tanf(view_angle / 2.0f);
     projection_matrix[0]  = f / aspect_ratio;
     projection_matrix[5]  = f;
     projection_matrix[10] = (z_far + z_near)/ (z_near - z_far);
     projection_matrix[11] = -1.0f;
     projection_matrix[14] = 2.0f * (z_far * z_near) / (z_near - z_far);
     glUniformMatrix4fv(uloc_project, 1, GL_FALSE, projection_matrix);

     /* Set the camera position */
     modelview_matrix[12]  = -5.0f;
     modelview_matrix[13]  = -5.0f;
     modelview_matrix[14]  = -20.0f;
     glUniformMatrix4fv(uloc_modelview, 1, GL_FALSE, modelview_matrix);

     /* Create mesh data */
     init_map();
     make_mesh(shader_program);

     /* Create vao + vbo to store the mesh */
     /* Create the vbo to store all the information for the grid and the height */

     /* setup the scene ready for rendering */
     glfwGetFramebufferSize(window, &width, &height);
     glViewport(0, 0, width, height);
     glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

     /* main loop */
     frame = 0;
     iter = 0;
     last_update_time = glfwGetTime();

     while (!glfwWindowShouldClose(window))
     {
         ++frame;
         /* render the next frame */
         glClear(GL_COLOR_BUFFER_BIT);
         glDrawElements(GL_LINES, 2* MAP_NUM_LINES , GL_UNSIGNED_INT, 0);

         /* display and process events through callbacks */
         glfwSwapBuffers(window);
         glfwPollEvents();
         /* Check the frame rate and update the heightmap if needed */
         dt = glfwGetTime();
         if ((dt - last_update_time) > 0.2)
         {
             /* generate the next iteration of the heightmap */
             if (iter < MAX_ITER)
             {
                 update_map(NUM_ITER_AT_A_TIME);
                 update_mesh();
                 iter += NUM_ITER_AT_A_TIME;
             }
             last_update_time = dt;
             frame = 0;
         }
     }

     glfwTerminate();
     exit(EXIT_SUCCESS);
 }
	//========================================================================
	// Heightmap example program using OpenGL 3 core profile
	// Copyright (c) 2010 Olivier Delannoy
	//
	// This software is provided 'as-is', without any express or implied
	// warranty. In no event will the authors be held liable for any damages
	// arising from the use of this software.
	//
	// Permission is granted to anyone to use this software for any purpose,
	// including commercial applications, and to alter it and redistribute it
	// freely, subject to the following restrictions:
	//
	// 1. The origin of this software must not be misrepresented; you must not
	// claim that you wrote the original software. If you use this software
	// in a product, an acknowledgment in the product documentation would
	// be appreciated but is not required.
	//
	// 2. Altered source versions must be plainly marked as such, and must not
	// be misrepresented as being the original software.
	//
	// 3. This notice may not be removed or altered from any source
	// distribution.
	//
	//========================================================================

	#include <stdlib.h>
	#include <stdio.h>
	#include <math.h>
	#include <assert.h>
	#include <stddef.h>

	#define GLAD_GL_IMPLEMENTATION
	#include <glad/gl.h>
	#define GLFW_INCLUDE_NONE
	#include <GLFW/glfw3.h>

	/* Map height updates */
	#define MAX_CIRCLE_SIZE (5.0f)
	#define MAX_DISPLACEMENT (1.0f)
	#define DISPLACEMENT_SIGN_LIMIT (0.3f)
	#define MAX_ITER (200)
	#define NUM_ITER_AT_A_TIME (1)

	/* Map general information */
	#define MAP_SIZE (10.0f)
	#define MAP_NUM_VERTICES (80)
	#define MAP_NUM_TOTAL_VERTICES (MAP_NUM_VERTICES*MAP_NUM_VERTICES)
	#define MAP_NUM_LINES (3* (MAP_NUM_VERTICES - 1) * (MAP_NUM_VERTICES - 1) + \
	2 * (MAP_NUM_VERTICES - 1))


	/**********************************************************************
	* Default shader programs
	*********************************************************************/

	static const char* vertex_shader_text =
	"#version 150\n"
	"uniform mat4 project;\n"
	"uniform mat4 modelview;\n"
	"in float x;\n"
	"in float y;\n"
	"in float z;\n"
	"\n"
	"void main()\n"
	"{\n"
	" gl_Position = project * modelview * vec4(x, y, z, 1.0);\n"
	"}\n";

	static const char* fragment_shader_text =
	"#version 150\n"
	"out vec4 color;\n"
	"void main()\n"
	"{\n"
	" color = vec4(0.2, 1.0, 0.2, 1.0); \n"
	"}\n";

	/**********************************************************************
	* Values for shader uniforms
	*********************************************************************/

	/* Frustum configuration */
	static GLfloat view_angle = 45.0f;
	static GLfloat aspect_ratio = 4.0f/3.0f;
	static GLfloat z_near = 1.0f;
	static GLfloat z_far = 100.f;

	/* Projection matrix */
	static GLfloat projection_matrix[16] = {
	1.0f, 0.0f, 0.0f, 0.0f,
	0.0f, 1.0f, 0.0f, 0.0f,
	0.0f, 0.0f, 1.0f, 0.0f,
	0.0f, 0.0f, 0.0f, 1.0f
	};

	/* Model view matrix */
	static GLfloat modelview_matrix[16] = {
	1.0f, 0.0f, 0.0f, 0.0f,
	0.0f, 1.0f, 0.0f, 0.0f,
	0.0f, 0.0f, 1.0f, 0.0f,
	0.0f, 0.0f, 0.0f, 1.0f
	};

	/**********************************************************************
	* Heightmap vertex and index data
	*********************************************************************/

	static GLfloat map_vertices[3][MAP_NUM_TOTAL_VERTICES];
	static GLuint map_line_indices[2*MAP_NUM_LINES];

	/* Store uniform location for the shaders
	* Those values are setup as part of the process of creating
	* the shader program. They should not be used before creating
	* the program.
	*/
	static GLuint mesh;
	static GLuint mesh_vbo[4];

	/**********************************************************************
	* OpenGL helper functions
	*********************************************************************/

	/* Creates a shader object of the specified type using the specified text
	*/
	static GLuint make_shader(GLenum type, const char* text)
	{
	GLuint shader;
	GLint shader_ok;
	GLsizei log_length;
	char info_log[8192];

	shader = glCreateShader(type);
	if (shader != 0)
	{
	glShaderSource(shader, 1, (const GLchar**)&text, NULL);
	glCompileShader(shader);
	glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_ok);
	if (shader_ok != GL_TRUE)
	{
	fprintf(stderr, "ERROR: Failed to compile %s shader\n", (type == GL_FRAGMENT_SHADER) ? "fragment" : "vertex" );
	glGetShaderInfoLog(shader, 8192, &log_length,info_log);
	fprintf(stderr, "ERROR: \n%s\n\n", info_log);
	glDeleteShader(shader);
	shader = 0;
	}
	}
	return shader;
	}

	/* Creates a program object using the specified vertex and fragment text
	*/
	static GLuint make_shader_program(const char* vs_text, const char* fs_text)
	{
	GLuint program = 0u;
	GLint program_ok;
	GLuint vertex_shader = 0u;
	GLuint fragment_shader = 0u;
	GLsizei log_length;
	char info_log[8192];

	vertex_shader = make_shader(GL_VERTEX_SHADER, vs_text);
	if (vertex_shader != 0u)
	{
	fragment_shader = make_shader(GL_FRAGMENT_SHADER, fs_text);
	if (fragment_shader != 0u)
	{
	/* make the program that connect the two shader and link it */
	program = glCreateProgram();
	if (program != 0u)
	{
	/* attach both shader and link */
	glAttachShader(program, vertex_shader);
	glAttachShader(program, fragment_shader);
	glLinkProgram(program);
	glGetProgramiv(program, GL_LINK_STATUS, &program_ok);

	if (program_ok != GL_TRUE)
	{
	fprintf(stderr, "ERROR, failed to link shader program\n");
	glGetProgramInfoLog(program, 8192, &log_length, info_log);
	fprintf(stderr, "ERROR: \n%s\n\n", info_log);
	glDeleteProgram(program);
	glDeleteShader(fragment_shader);
	glDeleteShader(vertex_shader);
	program = 0u;
	}
	}
	}
	else
	{
	fprintf(stderr, "ERROR: Unable to load fragment shader\n");
	glDeleteShader(vertex_shader);
	}
	}
	else
	{
	fprintf(stderr, "ERROR: Unable to load vertex shader\n");
	}
	return program;
	}

	/**********************************************************************
	* Geometry creation functions
	*********************************************************************/

	/* Generate vertices and indices for the heightmap
	*/
	static void init_map(void)
	{
	int i;
	int j;
	int k;
	GLfloat step = MAP_SIZE / (MAP_NUM_VERTICES - 1);
	GLfloat x = 0.0f;
	GLfloat z = 0.0f;
	/* Create a flat grid */
	k = 0;
	for (i = 0 ; i < MAP_NUM_VERTICES ; ++i)
	{
	for (j = 0 ; j < MAP_NUM_VERTICES ; ++j)
	{
	map_vertices[0][k] = x;
	map_vertices[1][k] = 0.0f;
	map_vertices[2][k] = z;
	z += step;
	++k;
	}
	x += step;
	z = 0.0f;
	}
	#if DEBUG_ENABLED
	for (i = 0 ; i < MAP_NUM_TOTAL_VERTICES ; ++i)
	{
	printf ("Vertice %d (%f, %f, %f)\n",
	i, map_vertices[0][i], map_vertices[1][i], map_vertices[2][i]);

	}
	#endif
	/* create indices */
	/* line fan based on i
	* i+1
	* \| / i + n + 1
	* \| /
	* \|/
	* i --- i + n
	*/

	/* close the top of the square */
	k = 0;
	for (i = 0 ; i < MAP_NUM_VERTICES -1 ; ++i)
	{
	map_line_indices[k++] = (i + 1) * MAP_NUM_VERTICES -1;
	map_line_indices[k++] = (i + 2) * MAP_NUM_VERTICES -1;
	}
	/* close the right of the square */
	for (i = 0 ; i < MAP_NUM_VERTICES -1 ; ++i)
	{
	map_line_indices[k++] = (MAP_NUM_VERTICES - 1) * MAP_NUM_VERTICES + i;
	map_line_indices[k++] = (MAP_NUM_VERTICES - 1) * MAP_NUM_VERTICES + i + 1;
	}

	for (i = 0 ; i < (MAP_NUM_VERTICES - 1) ; ++i)
	{
	for (j = 0 ; j < (MAP_NUM_VERTICES - 1) ; ++j)
	{
	int ref = i * (MAP_NUM_VERTICES) + j;
	map_line_indices[k++] = ref;
	map_line_indices[k++] = ref + 1;

	map_line_indices[k++] = ref;
	map_line_indices[k++] = ref + MAP_NUM_VERTICES;

	map_line_indices[k++] = ref;
	map_line_indices[k++] = ref + MAP_NUM_VERTICES + 1;
	}
	}

	#ifdef DEBUG_ENABLED
	for (k = 0 ; k < 2 * MAP_NUM_LINES ; k += 2)
	{
	int beg, end;
	beg = map_line_indices[k];
	end = map_line_indices[k+1];
	printf ("Line %d: %d -> %d (%f, %f, %f) -> (%f, %f, %f)\n",
	k / 2, beg, end,
	map_vertices[0][beg], map_vertices[1][beg], map_vertices[2][beg],
	map_vertices[0][end], map_vertices[1][end], map_vertices[2][end]);
	}
	#endif
	}

	static void generate_heightmap__circle(float* center_x, float* center_y,
	float* size, float* displacement)
	{
	float sign;
	/* random value for element in between [0-1.0] */
	center_x = (MAP_SIZE rand()) / (float) RAND_MAX;
	center_y = (MAP_SIZE rand()) / (float) RAND_MAX;
	size = (MAX_CIRCLE_SIZE rand()) / (float) RAND_MAX;
	sign = (1.0f * rand()) / (float) RAND_MAX;
	sign = (sign < DISPLACEMENT_SIGN_LIMIT) ? -1.0f : 1.0f;
	displacement = (sign (MAX_DISPLACEMENT * rand())) / (float) RAND_MAX;
	}

	/* Run the specified number of iterations of the generation process for the
	* heightmap
	*/
	static void update_map(int num_iter)
	{
	assert(num_iter > 0);
	while(num_iter)
	{
	/* center of the circle */
	float center_x;
	float center_z;
	float circle_size;
	float disp;
	size_t ii;
	generate_heightmap__circle(&center_x, &center_z, &circle_size, &disp);
	disp = disp / 2.0f;
	for (ii = 0u ; ii < MAP_NUM_TOTAL_VERTICES ; ++ii)
	{
	GLfloat dx = center_x - map_vertices[0][ii];
	GLfloat dz = center_z - map_vertices[2][ii];
	GLfloat pd = (2.0f * (float) sqrt((dx * dx) + (dz * dz))) / circle_size;
	if (fabs(pd) <= 1.0f)
	{
	/* tx,tz is within the circle */
	GLfloat new_height = disp + (float) (cos(pd3.14f)disp);
	map_vertices[1][ii] += new_height;
	}
	}
	--num_iter;
	}
	}

	/**********************************************************************
	* OpenGL helper functions
	*********************************************************************/

	/* Create VBO, IBO and VAO objects for the heightmap geometry and bind them to
	* the specified program object
	*/
	static void make_mesh(GLuint program)
	{
	GLuint attrloc;

	glGenVertexArrays(1, &mesh);
	glGenBuffers(4, mesh_vbo);
	glBindVertexArray(mesh);
	/* Prepare the data for drawing through a buffer inidices */
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mesh_vbo[3]);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint)* MAP_NUM_LINES * 2, map_line_indices, GL_STATIC_DRAW);

	/* Prepare the attributes for rendering */
	attrloc = glGetAttribLocation(program, "x");
	glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[0]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[0][0], GL_STATIC_DRAW);
	glEnableVertexAttribArray(attrloc);
	glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);

	attrloc = glGetAttribLocation(program, "z");
	glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[2]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[2][0], GL_STATIC_DRAW);
	glEnableVertexAttribArray(attrloc);
	glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);

	attrloc = glGetAttribLocation(program, "y");
	glBindBuffer(GL_ARRAY_BUFFER, mesh_vbo[1]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[1][0], GL_DYNAMIC_DRAW);
	glEnableVertexAttribArray(attrloc);
	glVertexAttribPointer(attrloc, 1, GL_FLOAT, GL_FALSE, 0, 0);
	}

	/* Update VBO vertices from source data
	*/
	static void update_mesh(void)
	{
	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(GLfloat) * MAP_NUM_TOTAL_VERTICES, &map_vertices[1][0]);
	}

	/**********************************************************************
	* GLFW callback functions
	*********************************************************************/

	static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
	{
	switch(key)
	{
	case GLFW_KEY_ESCAPE:
	/* Exit program on Escape */
	glfwSetWindowShouldClose(window, GLFW_TRUE);
	break;
	}
	}

	static void error_callback(int error, const char* description)
	{
	fprintf(stderr, "Error: %s\n", description);
	}

	int main(int argc, char** argv)
	{
	GLFWwindow* window;
	int iter;
	double dt;
	double last_update_time;
	int frame;
	float f;
	GLint uloc_modelview;
	GLint uloc_project;
	int width, height;

	GLuint shader_program;

	glfwSetErrorCallback(error_callback);

	if (!glfwInit())
	exit(EXIT_FAILURE);

	glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);

	window = glfwCreateWindow(800, 600, "GLFW OpenGL3 Heightmap demo", NULL, NULL);
	if (! window )
	{
	glfwTerminate();
	exit(EXIT_FAILURE);
	}

	/* Register events callback */
	glfwSetKeyCallback(window, key_callback);

	glfwMakeContextCurrent(window);
	gladLoadGL(glfwGetProcAddress);

	/* Prepare opengl resources for rendering */
	shader_program = make_shader_program(vertex_shader_text, fragment_shader_text);

	if (shader_program == 0u)
	{
	glfwTerminate();
	exit(EXIT_FAILURE);
	}

	glUseProgram(shader_program);
	uloc_project = glGetUniformLocation(shader_program, "project");
	uloc_modelview = glGetUniformLocation(shader_program, "modelview");

	/* Compute the projection matrix */
	f = 1.0f / tanf(view_angle / 2.0f);
	projection_matrix[0] = f / aspect_ratio;
	projection_matrix[5] = f;
	projection_matrix[10] = (z_far + z_near)/ (z_near - z_far);
	projection_matrix[11] = -1.0f;
	projection_matrix[14] = 2.0f * (z_far * z_near) / (z_near - z_far);
	glUniformMatrix4fv(uloc_project, 1, GL_FALSE, projection_matrix);

	/* Set the camera position */
	modelview_matrix[12] = -5.0f;
	modelview_matrix[13] = -5.0f;
	modelview_matrix[14] = -20.0f;
	glUniformMatrix4fv(uloc_modelview, 1, GL_FALSE, modelview_matrix);

	/* Create mesh data */
	init_map();
	make_mesh(shader_program);

	/* Create vao + vbo to store the mesh */
	/* Create the vbo to store all the information for the grid and the height */

	/* setup the scene ready for rendering */
	glfwGetFramebufferSize(window, &width, &height);
	glViewport(0, 0, width, height);
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

	/* main loop */
	frame = 0;
	iter = 0;
	last_update_time = glfwGetTime();

	while (!glfwWindowShouldClose(window))
	{
	++frame;
	/* render the next frame */
	glClear(GL_COLOR_BUFFER_BIT);
	glDrawElements(GL_LINES, 2* MAP_NUM_LINES , GL_UNSIGNED_INT, 0);

	/* display and process events through callbacks */
	glfwSwapBuffers(window);
	glfwPollEvents();
	/* Check the frame rate and update the heightmap if needed */
	dt = glfwGetTime();
	if ((dt - last_update_time) > 0.2)
	{
	/* generate the next iteration of the heightmap */
	if (iter < MAX_ITER)
	{
	update_map(NUM_ITER_AT_A_TIME);
	update_mesh();
	iter += NUM_ITER_AT_A_TIME;
	}
	last_update_time = dt;
	frame = 0;
	}
	}

	glfwTerminate();
	exit(EXIT_SUCCESS);
	}