---
layout: post
title:  "data_path"
date:   2016-05-23 05:04:00
categories: picrate update
permalink: methods/data_path.html
---
The purpose of the `data_path` wrapper is to provide the absolute data path to a sketches `data` folder. In vanilla processing the direct use of this method is discouraged, owing to the way it has been implemented (it is used internally and may be the cause file access issues in PiCrate). The `data_path` method is implemented in PiCrate, and does not rely on the vanilla-processing version.

### Simple usage ###

```ruby
#!/usr/bin/env jruby -w
require 'picrate'
class LoadImage < Processing::App
  def setup
    sketch_title 'Load Image'
    # The file "jelly.jpg" must be in the data folder
    # of the current sketch to load successfully
    @a = load_image(data_path('jelly.jpg'))
    no_loop # Makes draw only run once
  end

  def draw
    image @a, 0, 0
    image @a, @a.width, 0, @a.width / 2, @a.height / 2
  end

  def settings
    size 300, 200
  end
end

LoadImage.new
```

NB: it is equally valid to use `data_path` to provide an absolute path to the data folder on save (even when the data folder needs to be created on save).

### More sophisticated usage ###
You can use your ruby knowledge to 'dry up' vanilla processing sketches and to remove the need to type `data_path` many times in a sketch. Please note that we cannot rely on JRuby to convert an array of ruby-string to an array of java-string, this is why we need `glsl_files.to_java(:string)`. However the array of images does not require such an explicit conversion, _JRuby generally just does the right thing_.

```ruby
#!/usr/bin/env jruby -w
require 'picrate'
# Earth model with bump mapping, specular texture and dynamic cloud layer.
# Adapted from the THREE.js tutorial to processing by Andres Colubri,
# translated to PiCrate by Martin Prout:
# http://learningthreejs.com/blog/2013/09/16/how-to-make-the-earth-in-webgl/
class BlueMarble < Processing::App
  attr_reader :earth, :clouds, :earth_shader, :cloud_shader, :earth_rotation
  attr_reader :clouds_rotation, :target_angle

  SHADERS = %w(EarthFrag.glsl EarthVert.glsl CloudFrag.glsl CloudVert.glsl).freeze
  SHADER_NAME = %i(earth_frag earth_vert cloud_frag cloud_vert).freeze
  IMAGES = %w(earthmap1k earthcloudmap earthcloudmaptrans earthbump1k earthspec1k).freeze
  IMAGE_NAME = %i(earth_tex cloud_tex alpha_tex bump_map spec_map).freeze

  def setup
    sketch_title 'Blue Marble'
    @earth_rotation = 0
    @clouds_rotation = 0
    glsl_files = SHADERS.map { |shade| data_path(shade) }
    shaders = SHADER_NAME.zip(glsl_files.to_java(:string)).to_h
    images = IMAGES.map { |img| load_image(data_path("#{img}.jpg")) }
    textures = IMAGE_NAME.zip(images).to_h
    @earth_shader = load_shader(shaders[:earth_frag], shaders[:earth_vert])
    earth_shader.set('texMap', textures[:earth_tex])
    earth_shader.set('bumpMap', textures[:bump_map])
    earth_shader.set('specularMap', textures[:spec_map])
    earth_shader.set('bumpScale', 0.05)
    @cloud_shader = load_shader(shaders[:cloud_frag], shaders[:cloud_vert])
    cloud_shader.set('texMap', textures[:cloud_tex])
    cloud_shader.set('alphaMap', textures[:alpha_tex])
    @earth = create_shape(SPHERE, 200)
    earth.setStroke(false)
    earth.setSpecular(color(125))
    earth.setShininess(10)
    @clouds = create_shape(SPHERE, 201)
    clouds.setStroke(false)
  end

  def draw
    background(0)
    translate(width / 2, height / 2)
    point_light(255, 255, 255, 300, 0, 500)
    target_angle = map1d(mouse_x, (0..width), (0..TWO_PI))
    @earth_rotation += 0.05 * (target_angle - earth_rotation)
    shader(earth_shader)
    push_matrix
    rotate_y(earth_rotation)
    shape(earth)
    pop_matrix
    shader(cloud_shader)
    push_matrix
    rotate_y(earth_rotation + clouds_rotation)
    shape(clouds)
    pop_matrix
    @clouds_rotation += 0.001
  end

  def settings
    size(600, 600, P3D)
  end
end

BlueMarble.new
```