Overlaping Horizontal Bars Plotting example - built with Python+Cairo

overlaping-bars.py

#!/usr/bin/env python
# encoding: utf-8

# Python plotting "module" based in the graph found here:
# http://www.techdrivein.com/2012/09/chrome-overtakes-ie-to-become-worlds.html
#
# License: GPLv3
# Credits: Magnun Leno (@mind_bend)
# Site: http://www.mindbending.org

import cairo

LABELS = (
        "Chrome",
        "Internet Explorer",
        "Firefox",
        "Safari",
        "Opera",
        )

data = (
        0.283,
        0.276,
        0.228,
        0.144,
        0.022,
        )

colors = [
        (0.95, 0.20, 0.20),
        (0.99, 0.75, 0.30),
        (0.99, 0.96, 0.34),
        (0.72, 0.92, 0.23),
        (0.20, 0.41, 0.84),
        ]

# Image Size
X, Y = 700, 250

# Percentage of overlapping bars
OVERLAPPING = 0.2
# Alpha value for bars (transparency)
ALPHA = 0.85

# Graph padding
LEFT_PAD = 0.02
RIGHT_PAD = 0.05
TOP_PAD = 0.1
BOTTOM_PAD = 0.1
# Padding between text (label) and graph bars
TEXT_PAD = 0.02

TEXT_FONT = "Ubuntu"
BIG_FONT_SIZE = 16
SMALL_FONT_SIZE = 13

SORT_MAP = {}
for n, value in enumerate(data):
    SORT_MAP[value] = n

SORTED_DATA = sorted(SORT_MAP, reverse=True)

def draw_background(ctx, x1, y1):
    ctx.set_source_rgb(1.0, 1.0, 1.0)
    ctx.rectangle(0, 0, X, Y)
    ctx.fill()

def draw_labels(ctx, title, x0, y0):
    lwidth, lheight = ctx.text_extents(title)[2:4]
    ctx.set_source_rgb(0.15, 0.15, 0.15)
    ctx.move_to(x0 - lwidth, y0)
    ctx.show_text(title)

def draw_bar(ctx, x0, y0, w, h, color):
    ctx.set_source_rgba(*color)
    ctx.rectangle(x0, y0, w, h)
    ctx.fill()

def draw_blackbox(ctx, x0, y0, w, h):
    ctx.set_source_rgb(0.12, 0.12, 0.12)
    ctx.rectangle(x0, y0, w, h)
    ctx.fill()

def draw_percentage(ctx, x0, y0, text):
    ctx.select_font_face(TEXT_FONT, cairo.FONT_SLANT_NORMAL)
    ctx.set_font_size(SMALL_FONT_SIZE)
    ctx.set_source_rgb(0.9, 0.9, 0.9)
    ctx.move_to(x0, y0)
    ctx.show_text(text)


if __name__ == '__main__':
    # Initialize Cairo Surface and Context
    surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, X, Y)
    ctx = cairo.Context(surface)

    # Configure font
    ctx.select_font_face(TEXT_FONT, cairo.FONT_SLANT_OBLIQUE)
    ctx.set_font_size(BIG_FONT_SIZE)

    # Parametrize data values
    MAX_VALUE = max(data)
    data_param = [value/MAX_VALUE for value in data]

    # Calculates Label Max Text Size
    MAX_TEXT = max([ctx.text_extents(text)[2] for text in LABELS])

    # Convert percentage padding to real size
    LEFT_PADDING = LEFT_PAD * X
    RIGHT_PADDING = RIGHT_PAD * X
    TOP_PADDING = TOP_PAD * Y
    BOTTOM_PADDING = BOTTOM_PAD * Y
    TEXT_PADDING = X * TEXT_PAD

    # Usable graph space
    X_PLOT_SIZE = X - RIGHT_PADDING - LEFT_PADDING - MAX_TEXT
    Y_PLOT_SIZE = Y - TOP_PADDING - BOTTOM_PADDING

    # Usable height for each bar
    SLOT_SIZE = Y_PLOT_SIZE / len(SORTED_DATA)
    # Convert Overlapping percentage to real size
    OVERLAPPING = OVERLAPPING * SLOT_SIZE

    draw_background(ctx, X, Y)

    x0 = LEFT_PADDING
    y0 = TOP_PADDING
    ctx.select_font_face(TEXT_FONT, cairo.FONT_SLANT_NORMAL)
    ctx.set_font_size(SMALL_FONT_SIZE)
    for key in SORTED_DATA:
        n = SORT_MAP[key]
        value = data_param[n]

        # Calculates the "black box value"
        value_orig = data[n]
        p_value = '%.1f %%'%(value_orig*100)
        pvwidth, pvheight = ctx.text_extents(p_value)[2:4]
        ctx.select_font_face(TEXT_FONT, cairo.FONT_SLANT_OBLIQUE)
        ctx.set_font_size(BIG_FONT_SIZE)

        # Black box dimensions
        bb_pad_w = pvwidth*0.2
        bb_pad_h = pvheight*0.5
        bb_w = pvwidth + (2*bb_pad_w)
        bb_h = pvheight + (2*bb_pad_h)

        # Calculates the ending points
        x_bar_size = (X_PLOT_SIZE - bb_w) * value 
        y_bar_size = SLOT_SIZE + OVERLAPPING

        ########## Label
        title = LABELS[n]
        draw_labels(ctx, title, x0 + MAX_TEXT, y0 + (OVERLAPPING) + (SLOT_SIZE/2))

        ########## Horizontal Bar
        # Bars starting X point
        draw_bar(ctx, x0 + MAX_TEXT + TEXT_PADDING, y0, 
                x_bar_size, y_bar_size, colors[n] + (ALPHA, ))

        ########## Value's Black Box
        draw_blackbox(ctx, x0 + MAX_TEXT + TEXT_PADDING + x_bar_size, 
                y0 + (y_bar_size - bb_h)/2, bb_w, bb_h)

        ########## Value's Label
        draw_percentage(ctx, x0 + MAX_TEXT + TEXT_PADDING + x_bar_size + bb_pad_w,
                y0 + (y_bar_size - bb_h)/2 + pvheight + bb_pad_h, p_value)
        
        y0 += SLOT_SIZE

    surface.write_to_png("grafico.png")