Programación a nivel de lenguaje C
Este es un programa sobre el conjunto Mandelbrot extraido de esta página, que no daba ningún detalle de cómo compilarlo. Para poder compiarlo deben descargarse las librerias de OpenGL y Glut, el paquete de build-essentials y utilizar la instrucción:
$ gcc -o maldenbrot.o maldenbrot.c -lGL -lglut -lm
// Compilar con gcc -o maldenbrot.o maldenbrot.c -lGL -lglut -lm
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/glu.h>
void set_texture();
typedef struct {unsigned char r, g, b;} rgb_t;
rgb_t **tex = 0;
int gwin;
GLuint texture;
int width, height;
int tex_w, tex_h;
double scale = 1./256;
double cx = -.6, cy = 0;
int color_rotate = 0;
int saturation = 1;
int invert = 0;
int max_iter = 256;
void render()
{
double x = (double)width /tex_w,
y = (double)height/tex_h;
glClear(GL_COLOR_BUFFER_BIT);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
glBindTexture(GL_TEXTURE_2D, texture);
glBegin(GL_QUADS);
glTexCoord2f(0, 0); glVertex2i(0, 0);
glTexCoord2f(x, 0); glVertex2i(width, 0);
glTexCoord2f(x, y); glVertex2i(width, height);
glTexCoord2f(0, y); glVertex2i(0, height);
glEnd();
glFlush();
glFinish();
}
int dump = 1;
void screen_dump()
{
char fn[100];
int i;
sprintf(fn, "screen%03d.ppm", dump++);
FILE *fp = fopen(fn, "w");
fprintf(fp, "P6\n%d %d\n255\n", width, height);
for (i = height - 1; i >= 0; i--)
fwrite(tex[i], 1, width * 3, fp);
fclose(fp);
printf("%s written\n", fn);
}
void keypress(unsigned char key, int x, int y)
{
switch(key) {
case 'q': glFinish();
glutDestroyWindow(gwin);
return;
case 27: scale = 1./256; cx = -.6; cy = 0; break;
case 'r': color_rotate = (color_rotate + 1) % 6;
break;
case '>': case '.':
max_iter += 128;
if (max_iter > 1 << 15) max_iter = 1 << 15;
printf("max iter: %d\n", max_iter);
break;
case '<': case ',':
max_iter -= 128;
if (max_iter < 128) max_iter = 128;
printf("max iter: %d\n", max_iter);
break;
case 'c': saturation = 1 - saturation;
break;
case 's': screen_dump(); return;
case 'z': max_iter = 4096; break;
case 'x': max_iter = 128; break;
case ' ': invert = !invert;
}
set_texture();
}
void hsv_to_rgb(int hue, int min, int max, rgb_t *p)
{
if (min == max) max = min + 1;
if (invert) hue = max - (hue - min);
if (!saturation) {
p->r = p->g = p->b = 255 * (max - hue) / (max - min);
return;
}
double h = fmod(color_rotate + 1e-4 + 4.0 * (hue - min) / (max - min), 6);
# define VAL 255
double c = VAL * saturation;
double X = c * (1 - fabs(fmod(h, 2) - 1));
p->r = p->g = p->b = 0;
switch((int)h) {
case 0: p->r = c; p->g = X; return;
case 1: p->r = X; p->g = c; return;
case 2: p->g = c; p->b = X; return;
case 3: p->g = X; p->b = c; return;
case 4: p->r = X; p->b = c; return;
default:p->r = c; p->b = X;
}
}
void calc_mandel()
{
int i, j, iter, min, max;
rgb_t *px;
double x, y, zx, zy, zx2, zy2;
min = max_iter; max = 0;
for (i = 0; i < height; i++) {
px = tex[i];
y = (i - height/2) * scale + cy;
for (j = 0; j < width; j++, px++) {
x = (j - width/2) * scale + cx;
iter = 0;
zx = hypot(x - .25, y);
if (x < zx - 2 * zx * zx + .25) iter = max_iter;
if ((x + 1)*(x + 1) + y * y < 1/16) iter = max_iter;
zx = zy = zx2 = zy2 = 0;
for (; iter < max_iter && zx2 + zy2 < 4; iter++) {
zy = 2 * zx * zy + y;
zx = zx2 - zy2 + x;
zx2 = zx * zx;
zy2 = zy * zy;
}
if (iter < min) min = iter;
if (iter > max) max = iter;
*(unsigned short *)px = iter;
}
}
for (i = 0; i < height; i++)
for (j = 0, px = tex[i]; j < width; j++, px++)
hsv_to_rgb(*(unsigned short*)px, min, max, px);
}
void alloc_tex()
{
int i, ow = tex_w, oh = tex_h;
for (tex_w = 1; tex_w < width; tex_w <<= 1);
for (tex_h = 1; tex_h < height; tex_h <<= 1);
if (tex_h != oh || tex_w != ow)
tex = realloc(tex, tex_h * tex_w * 3 + tex_h * sizeof(rgb_t*));
for (tex[0] = (rgb_t *)(tex + tex_h), i = 1; i < tex_h; i++)
tex[i] = tex[i - 1] + tex_w;
}
void set_texture()
{
alloc_tex();
calc_mandel();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, 3, tex_w, tex_h,
0, GL_RGB, GL_UNSIGNED_BYTE, tex[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
render();
}
void mouseclick(int button, int state, int x, int y)
{
if (state != GLUT_UP) return;
cx += (x - width / 2) * scale;
cy -= (y - height/ 2) * scale;
switch(button) {
case GLUT_LEFT_BUTTON: /* zoom in */
if (scale > fabs(x) * 1e-16 && scale > fabs(y) * 1e-16)
scale /= 2;
break;
case GLUT_RIGHT_BUTTON: /* zoom out */
scale *= 2;
break;
/* any other button recenters */
}
set_texture();
}
void resize(int w, int h)
{
printf("resize %d %d\n", w, h);
width = w;
height = h;
glViewport(0, 0, w, h);
glOrtho(0, w, 0, h, -1, 1);
set_texture();
}
void init_gfx(int *c, char **v)
{
glutInit(c, v);
glutInitDisplayMode(GLUT_RGB);
glutInitWindowSize(640, 480);
glutDisplayFunc(render);
gwin = glutCreateWindow("Mandelbrot");
glutKeyboardFunc(keypress);
glutMouseFunc(mouseclick);
glutReshapeFunc(resize);
glGenTextures(1, &texture);
set_texture();
}
int main(int c, char **v)
{
init_gfx(&c, v);
printf("keys:\n\tr: color rotation\n\tc: monochrome\n\ts: screen dump\n\t"
"<, >: decrease/increase max iteration\n\tq: quit\n\tmouse buttons to zoom\n");
glutMainLoop();
return 0;
}
