/*
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * author: Jerome Glisse
 */
#define MAXFRAME        5
#define PFINISH         1
#define MAX_PARTICLES   256

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define GL_GLEXT_PROTOTYPES
#include <GL/glew.h>
#include <GL/glut.h>

struct particle {
    float   pos[4];
    float   vel[4];
};

static struct particle *particles;

static GLuint particle_buffer[2];
static GLuint tfb_shader_prog;
static GLuint tfb_vs_shader;
static GLuint random_tex;

static GLint  ptime = 0;
static GLfloat pdt = 0.0f;
static GLuint curr_vb = 0;
static GLuint frames = 0;
static GLuint win_width = 1024;
static GLuint win_height = 1024;

static GLint attrib_velocity;
static GLint uni_delta_time_ms;
static GLint uni_tex;

static const char tfb_shader_src[] =
    "#version 120                                                                        \n"
    "                                                                                    \n"
    "attribute vec4 velocity;                                                            \n"
    "attribute float age;                                                                \n"
    "                                                                                    \n"
    "varying vec4 ovelocity;                                                             \n"
    "                                                                                    \n"
    "uniform float dt;                                                                   \n"
    "uniform sampler1D tex;                                                              \n"
    "                                                                                    \n"
    "void main()                                                                         \n"
    "{                                                                                   \n"
    "    if (velocity.w > 5.0) {                                                         \n"
    "        ovelocity = texture1D(tex, ovelocity.w);                                    \n"
    "        ovelocity -= vec4(0.5, 0.5, 0.5, 0.5);                                      \n"
    "        gl_Position = ovelocity * dt;                                               \n"
    "    } else {                                                                        \n"
    "        ovelocity = velocity;                                                       \n"
    "        ovelocity.w = velocity.w + dt;                                              \n"
    "        gl_Position.xyz = gl_Vertex.xyz + velocity.xyz * dt;                        \n"
    "    }                                                                               \n"
    "}                                                                                   \n";

static void particles_update(void)
{
    glUseProgram(tfb_shader_prog);
    glUniform1f(uni_delta_time_ms, pdt);
    glUniform1i(uni_tex, 0);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_1D, random_tex);

    glBindBuffer(GL_ARRAY_BUFFER, particle_buffer[curr_vb]);
    glEnableVertexAttribArray(attrib_velocity);
    glVertexAttribPointer(attrib_velocity, 4, GL_FLOAT, GL_FALSE, sizeof(struct particle), (const GLvoid*)16);
    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(4, GL_FLOAT, sizeof(struct particle), 0);

    glEnable(GL_RASTERIZER_DISCARD);
    glBindBufferBaseEXT(GL_TRANSFORM_FEEDBACK_BUFFER, 0, particle_buffer[(curr_vb + 1) & 1]);
    glBeginTransformFeedback(GL_POINTS);
    glDrawArrays(GL_POINTS, 0, MAX_PARTICLES);
    glEndTransformFeedback();

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableVertexAttribArray(attrib_velocity);
    glDisable(GL_RASTERIZER_DISCARD);
    glUseProgram(0);

    /* swap */
    curr_vb = (curr_vb + 1) & 1;
    ptime += pdt;
}

void particle_draw()
{
    float ar;

    ar = (float)win_width / win_height;
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-ar, ar, -1.0, 1.0, 5.0, 60.0);
    glMatrixMode(GL_MODELVIEW);
    glPointSize(8.0);

    glColor3f(0,1,0);
    glBindBuffer(GL_ARRAY_BUFFER, particle_buffer[curr_vb]);
    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, sizeof(struct particle), 0);
    glDrawArrays(GL_POINTS, 0, MAX_PARTICLES);
    glDisableClientState(GL_VERTEX_ARRAY);
}

static void draw(void)
{
#if PFINISH
    fprintf(stderr, "EE TFB -------------------------------------------------------\n");
#endif
    particles_update();
#if PFINISH
    glFinish();
    fprintf(stderr, "EE TFB _______________________________________________________\n");
#endif

#if PFINISH
    fprintf(stderr, "EE CLEAR -----------------------------------------------------\n");
#endif
    glClear(GL_COLOR_BUFFER_BIT);
#if PFINISH
    glFinish();
    fprintf(stderr, "EE CLEAR _____________________________________________________\n");
#endif


#if PFINISH
    fprintf(stderr, "EE DRAW ------------------------------------------------------\n");
#endif
    particle_draw();
#if PFINISH
    glFinish();
    fprintf(stderr, "EE DRAW ______________________________________________________\n");
#endif

    glutSwapBuffers();
    frames++;
    if (frames >= MAXFRAME) {
        glFinish();
        exit(0);
    }
}

static void idle(void)
{
    static double t0 = -1.;
    double dt, t;

    t = glutGet(GLUT_ELAPSED_TIME) / 1000.0;
    if (t0 < 0.0)
        t0 = t;
    dt = t - t0;
    t0 = t;
    pdt = dt;

    glutPostRedisplay();
}

/* new window size or exposure */
static void reshape(int width, int height)
{
    GLfloat h = (GLfloat) height / (GLfloat) width;

    glViewport(0, 0, (GLint) width, (GLint) height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-1.0, 1.0, -h, h, 5.0, 60.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -40.0);

    win_width = width;
    win_height = height;
}

float random_0to1(void)
{
    return (float)rand() / RAND_MAX;
}

static void init(void)
{
    size_t particles_size;
    const GLchar *p[1];
    GLint len[1];
    GLint status;
    const GLchar* varyings[4];
    unsigned texsize = 512;
    float *randomtex;

    glDisable(GL_DEPTH_TEST);

    /* random texture */
    srand(glutGet(GLUT_ELAPSED_TIME));
    randomtex = malloc(texsize * 4 * 4);
    if (randomtex == NULL) {
        exit(1);
    }
    for (unsigned i = 0 ; i < (texsize * 4); i++) {
        randomtex[i] = random_0to1();
    }
    glGenTextures(1, &random_tex);
    glBindTexture(GL_TEXTURE_1D, random_tex);
    glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, texsize, 0.0f, GL_RGBA, GL_FLOAT, randomtex);
    glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    free(randomtex);
    glBindTexture(GL_TEXTURE_1D, 0);

    particles_size = sizeof(*particles) * MAX_PARTICLES;
    particles = malloc(particles_size);
    if (particles == NULL) {
        exit(-ENOMEM);
    }
    glGenBuffers(2, particle_buffer);
    for (unsigned i = 0; i < MAX_PARTICLES; i++) {
        particles[i].pos[0] = random_0to1();
        particles[i].pos[1] = random_0to1();
        particles[i].pos[2] = random_0to1();
        particles[i].pos[3] = 0.0f;
        particles[i].vel[0] = random_0to1() - 0.5f;
        particles[i].vel[1] = random_0to1() - 0.5f;
        particles[i].vel[2] = random_0to1() - 0.5f;
        particles[i].vel[3] = random_0to1() - 0.5f;
    }
    for (unsigned i = 0; i < 2 ; i++) {
        glBindBuffer(GL_ARRAY_BUFFER, particle_buffer[i]);
        glBufferData(GL_ARRAY_BUFFER, particles_size, particles, GL_DYNAMIC_DRAW);
    }
    free(particles);

#if 1
    /* tfb shader */
    tfb_shader_prog = glCreateProgram();
    tfb_vs_shader = glCreateShader(GL_VERTEX_SHADER);
    p[0] = tfb_shader_src;
    len[0] = strlen(tfb_shader_src);
    glShaderSource(tfb_vs_shader, 1, p, len);
    glCompileShader(tfb_vs_shader);
    glGetShaderiv(tfb_vs_shader, GL_COMPILE_STATUS, &status);
    if (!status) {
        GLchar log[1024];

        glGetShaderInfoLog(tfb_vs_shader, 1024, NULL, log);
        fprintf(stderr, "Error compiling tfb vs shader %s: \n", log);
        exit(1);
    }
    glAttachShader(tfb_shader_prog, tfb_vs_shader);

    /* tfb linking */
    varyings[0] = "gl_Position";
    varyings[1] = "ovelocity";
    glTransformFeedbackVaryings(tfb_shader_prog, 2, varyings, GL_INTERLEAVED_ATTRIBS);

    glLinkProgram(tfb_shader_prog);
    glGetProgramiv(tfb_shader_prog, GL_LINK_STATUS, &status);
    if (!status) {
        GLchar log[1024];

        glGetProgramInfoLog(tfb_shader_prog, 1024, NULL, log);
        fprintf(stderr, "Error linking tfb shader %s: \n", log);
        exit(1);
    }
    glValidateProgram(tfb_shader_prog);
    glGetProgramiv(tfb_shader_prog, GL_VALIDATE_STATUS, &status);
    if (!status) {
        GLchar log[1024];

        glGetProgramInfoLog(tfb_shader_prog, 1024, NULL, log);
        fprintf(stderr, "Invalid tfb shader program %s: \n", log);
        exit(1);
    }
    uni_delta_time_ms = glGetUniformLocation(tfb_shader_prog, "dt");
    uni_tex = glGetUniformLocation(tfb_shader_prog, "tex");

    attrib_velocity = glGetAttribLocation(tfb_shader_prog, "velocity");
    if (attrib_velocity == -1) {
        fprintf(stderr, "invalid attribute location %d\n", attrib_velocity);
        exit(-1);
    }
#endif
}

static void key(unsigned char k, int x, int y)
{
  switch (k) {
  case 27:  /* Escape */
      exit(0);
      break;
  default:
      return;
  }
  glutPostRedisplay();
}

int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE | GLUT_STENCIL);
    glutInitWindowSize(win_width, win_height);
    glutCreateWindow("glgears");

    GLenum err = glewInit();
    if (GLEW_OK != err) {
        fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
        return -1;
    }
    if (!GLEW_EXT_transform_feedback) {
        fprintf(stderr, "EXT_transform_feedback not supported\n");
        return -1;
    }

    glutKeyboardFunc(key);
    glutIdleFunc(idle);
    glutReshapeFunc(reshape);
    glutDisplayFunc(draw);

    init();
    reshape(win_width, win_height);
    glutMainLoop();
    return 0;
}