import sys, Image
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *

viewRotZ = 0
viewRotX = 0

import random

seed = 0
if len(sys.argv) > 1:
    seed = int(sys.argv[1])


def makeHeightField(level):
    random.seed(seed)
    size = 2**level + 1
    h = [[0]*size for _ in range(0,size)]
    displacement = 4.0
    for l in range(level-1, -1, -1):
        step = 2**l
        for i in range(0, size, step*2):
            for j in range(step, size, step*2):
                h[i][j] = (h[i][j-step]+h[i][j+step])/2.0 + random.gauss(0,displacement)
        for i in range(step, size, step*2):
            for j in range(0, size, step*2):
                h[i][j] = (h[i-step][j]+h[i+step][j])/2.0 + random.gauss(0,displacement)
        for i in range(step, size, step*2):
            for j in range(step, size, step*2):
                h[i][j] = (h[i-step][j]+h[i+step][j]+h[i][j-step]+h[i][j+step])/4.0 + random.gauss(0,displacement)
        displacement /= 1.8
    return h


def makeTerrain(level):
    hf = makeHeightField(level)
    size = len(hf)
    dl = glGenLists(1)
    glNewList(dl, GL_COMPILE)
    glTranslatef(-16, -16, 0)
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)
    scale = 32 / (size-1.0)
    for i in range(0,size):
        for j in range(0,size):
            if hf[i][j] < 0:
                hf[i][j] = -0.01
    for i in range(0,size-1):
        glBegin(GL_TRIANGLE_STRIP)
        for j in range(0,size):
            if hf[i][j] >= 0: glColor3f(0.3, 1, 0.2)
            else: glColor3f(0, 0, 0.8)
            glVertex3f(i*scale,j*scale,hf[i][j])
            if hf[i+1][j] >= 0: glColor3f(0.3, 1, 0.2)
            else: glColor3f(0, 0, 0.8)
            glVertex3f((i+1)*scale,j*scale,hf[i+1][j])
        glEnd()
    glEndList()
    return dl

def draw():
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluPerspective(50.0, 1.0, 1.0, 100.0)
    glMatrixMode(GL_MODELVIEW)

    glLoadIdentity()
    glTranslatef(0.0, 0.0, -30.0)
    glRotatef(viewRotX, 1.0, 0.0, 0.0)
    glRotatef(viewRotZ, 0.0, 0.0, 1.0)
    
    glCallList(terrain)
    glutSwapBuffers()


level = 0

def keyboard(key, x, y):
    global level, terrain
    if key == chr(27):
        sys.exit(0)
    elif key == '+':
        level += 1
        terrain = makeTerrain(level)
    elif key == '-' and level>0:
        level -= 1
        terrain = makeTerrain(level)
    glutPostRedisplay()
        

def specialkey(key,x,y):
    global viewRotX, viewRotZ
    if key == GLUT_KEY_LEFT:
        viewRotZ = viewRotZ + 3
    elif key == GLUT_KEY_RIGHT:
        viewRotZ = viewRotZ - 3
    elif key == GLUT_KEY_UP:
        viewRotX = viewRotX + 3
    elif key == GLUT_KEY_DOWN:
        viewRotX = viewRotX - 3
    glutPostRedisplay()

glutInit([])
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH)
glutInitWindowSize(400,400)
glutCreateWindow(sys.argv[0])
glutDisplayFunc(draw)
glutKeyboardFunc(keyboard)
glutSpecialFunc(specialkey)
glEnable(GL_DEPTH_TEST)
terrain = makeTerrain(level)
glutMainLoop()