#+TITLE: Python CAD Tutorial 07 - Drawing a grid 
#+DATE: 2013-10-07 12:00:00 UTC
#+DESCRIPTION: Drawing a grid in 3d space using gl lines
#+FILETAGS: GTK-3:python:cad:opengl
#+CATEGORY: python
#+SLUG: 07-cad-drawing-a-grid
#+THUMBNAIL: ../../../images/cad/tut07-interface.png
#+BEGIN_COMMENT
.. title: Python CAD Tutorial 07 - Drawing a grid 
.. slug: 07-cad-drawing-a-grid.org
.. date: 2013-10-07 12:00:00 UTC
.. tags: GTK-3, python, cad, opengl
.. category: python
.. description: Drawing a grid in 3d space using gl lines
.. type: text
#+END_COMMENT

[[https://code.launchpad.net/~oly/fabricad/tut07][View/Download Code]]


#+CAPTION: Grid 
[[../../../images/cad/tut07-interface.png]]

We created a plane in the previous tutorial. Now we will inherit that class to create a grid, at a later stage we will add snap to grid functionality.The new grid class will take three parameters: a centre point, a spacing value and a size value. We will set the size value to be the size of the viewport and will set a default spacing between the lines.The new methods for the class are below:

 + The grid_spacing method shifts the lines by the amount specified in the spacing parameter until the maximum size has been reached.
 + The draw method draws lines to make up the grid. On every tenth line it changes the colour to a darker line.

Future tutorials will deal with snap to grid functionality and auto calculating based on the zoom level, but for now we have something to work with.

#+BEGIN_SRC python
import math

from point import createpoint
from plane import createplanesimple


class creategrid:
    display_color = (0.6, 0.6, 0.6)
    
    large_grid = 10
    small_grid = 2.5

    def __init__(self, p1, spacing=1.5, size=65):
        self.plane = createplanesimple(p1, size * 2)
        self.p1 = createpoint(p1)
        self.normal = createpoint((0, 1, 0))
        self.size = size
        self.small_grid = spacing
        self.large_grid = spacing * 10

    def grid_spacing(self):
        #work out how many times the grid units fit inside our grid size and make it a whole number
        size =  math.ceil(self.size / self.small_grid) * self.small_grid
        #adjust x by size so we can draw the lines
        x = self.p1.x - size
        #loop from start until our lines are greater than our max size
        while x < (self.p1.x + size):
            x += self.small_grid
            yield x

    def draw(self):
        self.plane.draw()
        glColor3f(*self.display_color)
        glBegin(GL_LINES)

        for item in self.grid_spacing():
            #coordinate modulus large_grid (returns 0 if there is no remaineder), so lets draw a different colour line
            if (item % self.large_grid) == 0:
                glColor3f(0.4, 0.4, 0.4)
            else:
                glColor3f(*self.display_color)

            glVertex3f(item, self.p1.y - self.size, self.p1.z)
            glVertex3f(item, self.p1.y + self.size, self.p1.z)

            glVertex3f(self.p1.x - self.size, item, self.p1.z)
            glVertex3f(self.p1.x + self.size, item, self.p1.z)
        glEnd()
#+END_SRC