PathDemo

Using CGContextBeginPath and related APIs

Sources

DemoView.py

from Cocoa import *
from Quartz import *

import objc

from math import pi as PI
import random

class DemoView (NSView):
    _demoNumber = objc.ivar(objc._C_INT)


    def initWithFrame_(self, frameRect):
        self = super(DemoView, self).initWithFrame_(frameRect)
        if self is None:
            return None

        self._demoNumber = 0
        return self

    def drawRect_(self, rect):
        context = NSGraphicsContext.currentContext().graphicsPort()

        CGContextSetGrayFillColor(context, 1.0, 1.0)
        CGContextFillRect(context, rect)

        if self._demoNumber == 0:
            rectangles(context, rect)

        elif self._demoNumber == 1:
            circles(context, rect)

        elif self._demoNumber == 2:
            bezierPaths(context, rect)

        elif self._demoNumber == 3:
            circleClipping(context, rect)

        else:
            NSLog("Invalid demo number.")

    def setDemoNumber_(self, number):
        self._demoNumber = number


# The various demo functions

def setRandomFillColor(context):
    CGContextSetRGBFillColor(context,
           random.uniform(0, 1), random.uniform(0, 1),
           random.uniform(0, 1), random.uniform(0, 1))

def setRandomStrokeColor(context):
    CGContextSetRGBStrokeColor(context,
           random.uniform(0, 1), random.uniform(0, 1),
           random.uniform(0, 1), random.uniform(0, 1))


def randomPointInRect(rect):
    return CGPoint(
        x = random.uniform(CGRectGetMinX(rect), CGRectGetMaxX(rect)),
        y = random.uniform(CGRectGetMinY(rect), CGRectGetMaxY(rect)))

def randomRectInRect(rect):
    p = randomPointInRect(rect)
    q = randomPointInRect(rect)
    return CGRectMake(p.x, p.y, q.x - p.x, q.y - p.y)

def rectangles(context, rect):
    # Draw random rectangles (some stroked, some filled).

    for k in range(20):
        if k % 2 == 0:
            setRandomFillColor(context)
            CGContextFillRect(context, randomRectInRect(rect))

        else:
            setRandomStrokeColor(context)
            CGContextSetLineWidth(context, 2 + random.randint(0, 10))
            CGContextStrokeRect(context, randomRectInRect(rect))

def circles(context, rect):
    # Draw random circles (some stroked, some filled).

    for k in range(20):
        r = randomRectInRect(rect)
        w = CGRectGetWidth(r)
        h = CGRectGetHeight(r)
        CGContextBeginPath(context)

        if w < h:
            v = w
        else:
            v = h

        CGContextAddArc(context,
                CGRectGetMidX(r), CGRectGetMidY(r),
                v, 0, 2*PI, False)
        CGContextClosePath(context)

        if k % 2 == 0:
            setRandomFillColor(context)
            CGContextFillPath(context)

        else:
            setRandomStrokeColor(context)
            CGContextSetLineWidth(context, 2 + random.randint(0, 10))
            CGContextStrokePath(context)

def bezierPaths(context, rect):
    for k in range(20):
        numberOfSegments = 1 + random.randint(0, 8)
        CGContextBeginPath(context)
        p = randomPointInRect(rect)
        CGContextMoveToPoint(context, p.x, p.y)
        for j in range(numberOfSegments):
            p = randomPointInRect(rect);

            if j % 2 == 0:
                CGContextAddLineToPoint(context, p.x, p.y)

            else:
                c1 = randomPointInRect(rect)
                c2 = randomPointInRect(rect)
                CGContextAddCurveToPoint(context, c1.x, c1.y,
                                         c2.x, c2.y, p.x, p.y)

        if k % 2 == 0:
            setRandomFillColor(context)
            CGContextClosePath(context)
            CGContextFillPath(context)

        else:
            setRandomStrokeColor(context)
            CGContextSetLineWidth(context, 2 + random.randint(0, 10))
            CGContextStrokePath(context)


def circleClipping(context, rect):
    # Draw a random path through a circular clip.

    w = CGRectGetWidth(rect)
    h = CGRectGetHeight(rect)
    CGContextBeginPath(context)
    if w < h:
        v = w
    else:
        v = h
    CGContextAddArc(context, CGRectGetMidX(rect), CGRectGetMidY(rect),
                    v/2, 0, 2*PI, False)
    CGContextClosePath(context)
    CGContextClip(context)

    # Draw something into the clip.
    bezierPaths(context, rect)

    # Draw a clip path on top as a black stroked circle.
    CGContextBeginPath(context)
    CGContextAddArc(context, CGRectGetMidX(rect), CGRectGetMidY(rect),
                    v/2, 0, 2*PI, False)
    CGContextClosePath(context)
    CGContextSetLineWidth(context, 1)
    CGContextSetRGBStrokeColor(context, 0, 0, 0, 1)
    CGContextStrokePath(context)

PathDemoController.py

from Cocoa import *
import objc

class PathDemoController (NSObject):
    button      = objc.ivar()
    popup       = objc.ivar()
    window      = objc.ivar()
    demoView    = objc.ivar()

    def awakeFromNib(self):
        #  Add the title of your new demo to the END of this array.

        titles = [ 'Rectangles', 'Circles', 'Bezier Paths', 'Circle Clipping' ]

        self.popup.removeAllItems()

        for t in titles:
            self.popup.addItemWithTitle_(t)

    @objc.IBAction
    def runAgain_(self, sender):
        self.select_(self)

    @objc.IBAction
    def select_(self, sender):
        self.demoView.setDemoNumber_(self.popup.indexOfSelectedItem())
        self.demoView.setNeedsDisplay_(True)

    def applicationShouldTerminateAfterLastWindowClosed_(self, application):
        return True

main.py

from PyObjCTools import NibClassBuilder, AppHelper

NibClassBuilder.extractClasses("MainMenu")

import DemoView
import PathDemoController

AppHelper.runEventLoop()

setup.py

"""
Script for building the example.

Usage:
    python setup.py py2app
"""
from distutils.core import setup
import py2app

setup(
    name='PathDemo',
    app=["main.py"],
    data_files=["English.lproj"],
)

Resources

• Download example