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Understanding How to use CairoThe best way to understand how to use cairo is to imagine that you are anartist using a paintbrush to draw out a shape on canvas.To begin, you can choose a few characteristics of your brush. You can choosethe thickness of your brush and the colour you want to paint with. You canalso choose the shape of your brush tip - You can choose either a circle or asquare.Once you have chosen your brush, you are ready to start painting. You have tobe quite precise when describing what you want to appear.Firstly, decide where you want to place your brush on the canvas. You do thisby supplying an x & y coordinate. Next you define how you want your brushstroke to look - an arc, a straight line etc.

Finally you define the pointwhere you want your stoke to end, again by supplying an x & y coordinate.Triangles and squares are very easy to do!More complex graphics are generated using variations of the above theme with afew additions such as Fills (colouring in), transformations (zooming in,moving) etc. Download auteurs learned love bootboys rar. Using the Python interface to cairoNearly all the work revolves around using the (orcairot in the cairo C API). This is the object that you send your drawingcommands to. There are a few options available to initialize this object indifferent ways. Initializing the cairo.Context Object.One Very Important thing to realize is there is a difference between thecoordinates you are describing your graphics on and the coordinates you willbe displaying your graphic on.(Ex - When giving a presentation you draw on your transparent acetate beforehand, and then display it on your overhead projector - cairo calls thetransparent acetate the user space coordinates and the projected image thedevice space coordinates)On initializing the cairo context object, we tell it how to transform ourdescription to how it should be displayed. To do this we supply atransformation matrix. Modifying the transformation matrix can lead to somevery interesting results.One of cairo’s most powerful features is that it can output graphics in manydifferent formats (it can use multiple back ends).

For printing, we can havecairo translate our graphics into Postscript to be sent off to the printer.For on screen display, we can have cairo translate our graphics intosomething glitz can understand for hardware accelerated rendering! It hasmany more important and useful target back ends. On initializing the, we set its target back end, supplying a few details(such as colour depth and size), as in the example below. #!/usr/bin/env python import math import cairo WIDTH, HEIGHT = 256, 256 surface = cairo. ImageSurface ( cairo. FORMATARGB32, WIDTH, HEIGHT ) ctx = cairo.

Context ( surface ) ctx. Scale ( WIDTH, HEIGHT ) # Normalizing the canvas pat = cairo. LinearGradient ( 0.0, 0.0, 0.0, 1.0 ) pat. Addcolorstoprgba ( 1, 0.7, 0, 0, 0.5 ) # First stop, 50% opacity pat. Addcolorstoprgba ( 0, 0.9, 0.7, 0.2, 1 ) # Last stop, 100% opacity ctx. Rectangle ( 0, 0, 1, 1 ) # Rectangle(x0, y0, x1, y1) ctx.

Setsource ( pat ) ctx. Translate ( 0.1, 0.1 ) # Changing the current transformation matrix ctx. Moveto ( 0, 0 ) # Arc(cx, cy, radius, startangle, stopangle) ctx. Arc ( 0.2, 0.1, 0.1, - math.

Pi / 2, 0 ) ctx. Lineto ( 0.5, 0.1 ) # Line to (x,y) # Curve(x1, y1, x2, y2, x3, y3) ctx. Curveto ( 0.5, 0.2, 0.5, 0.4, 0.2, 0.8 ) ctx.

Closepath ctx. Setsourcergb ( 0.3, 0.2, 0.5 ) # Solid color ctx. Setlinewidth ( 0.02 ) ctx. Stroke surface. Writetopng ( 'example.png' ) # Output to PNG.