// Osa 5. Tekijä: Juha-Pekka Jokela <jpjokela@gmail.com>
#include <assert.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>
#include <GL/gl.h>

#define FLOATS_VERTEX 3
#define VERTICES_LINE 2

struct MyModel *model;

struct MyModel
{
	GLenum primitive; /* Tyyppi, mina piirretaan */
	GLfloat *vertices;/* Taulukko, jossa verteksit */
	GLuint *indexes;  /* Taulukko, jossa indeksit */
	GLsizei count;    /* Indeksien lukumaara */
};

static void DeleteModel(struct MyModel *m)
{
	if(m)
	{
		free(m->vertices);
		free(m->indexes);
		free(m);
	}
}
/* Tekee esimerkkimallin argumenttien perusteella */
static struct MyModel *CreateModel(unsigned int numlines, GLfloat size)
{
	struct MyModel *m=malloc(sizeof(struct MyModel));
	if(m)
	{
		m->primitive=GL_LINES;
		m->indexes=NULL;
		m->vertices=malloc(sizeof(float[FLOATS_VERTEX*(numlines+1)]));
		if(m->vertices)
		{
			unsigned int l;
			// Keskusta
			m->vertices[0*FLOATS_VERTEX+0]=0.0f;
			m->vertices[0*FLOATS_VERTEX+1]=0.0f;
			m->vertices[0*FLOATS_VERTEX+2]=0.0f;
			for(l=1; l<=numlines; ++l)
			{
				float angle=(float)l/(float)numlines*M_PI*2;
				m->vertices[l*FLOATS_VERTEX+0]=size/2.0f*sinf(angle);
				m->vertices[l*FLOATS_VERTEX+1]=size/2.0f*cosf(angle);
				m->vertices[l*FLOATS_VERTEX+2]=0.0f;
			}
			m->count=numlines*VERTICES_LINE;
			m->indexes=malloc(sizeof(GLuint[m->count]));
			if(m->indexes)
			{
				unsigned int l;
				for(l=0; l<numlines; ++l)
				{
					m->indexes[l*VERTICES_LINE+0]=0;
					m->indexes[l*VERTICES_LINE+1]=l+1;
				}
				return m;
			}
		}
	}
	DeleteModel(m);
	return m;
}

static void DrawModel(const struct MyModel *m)
{
	if(m)
	{
		/* Maaritellaan verteksitaulukko kayttoon */
		glEnableClientState(GL_VERTEX_ARRAY);
		/* Maaritellaan verteksitaulukon sijainti */
		glVertexPointer(3, GL_FLOAT, 0, m->vertices);
		/* Piirretaan indeksitaulukon maarittamat verteksit */
		glDrawElements(m->primitive, m->count, GL_UNSIGNED_INT, m->indexes);
	}
}

static void Display(void)
{
	glClear(GL_COLOR_BUFFER_BIT);
	DrawModel(model);
	glutSwapBuffers();
	/* Varmistetaan, ettei ole tullut ajonaikaisia OpenGL virheita */
	assert(!glGetError());
}

int main(int argc, char *argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
	glutInitWindowSize(640, 480);
	glutCreateWindow("Saku");
	glutDisplayFunc(Display);
	model=CreateModel(40, 2.0f);
	glutMainLoop();
	DeleteModel(model);
	return 0;
}