Simple Drawing Functions Offered by GTK+3 and Cairo

The script shows how to draw simple shapes on a GTK+3 drawing area using Python3.

  

1. Define a drawing area using Gtk.DrawingArea().
2. Setting color using set_source_rgb().
3. Drawing circles with arc().
4. Moving the drawing tip with move_to().
5. Drawing lines with line_to().
6. Drawing rectangles with rectangle().
7. Drawing the outline of a shape and filling the content of the shape with stoke() and fill() respectively.
8. Setting the line width with set_line_width().
9. Setting line dash with set_dash().

Reference

Basic Drawing in PyCairo

Source Code

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#!/usr/bin/env python3 import gi gi.require_version('Gtk','3.0') from gi.repository import Gtk import math, cairo, random # default dimensions of the application window gWidth = 800 gHeight = 600 # margins(top, bottom, left, right) # between the sides of the drawable area # and the Cartesian plane gMargins = (20,20,50,50) # colors to be used gColor1 = (255, 235, 153) gColor2 = (204, 163, 0) gColor3 = (102, 82, 0) gColor4 = (255, 153, 0) gColor_b50 = (128, 128, 128) gColor_b100 = (0, 0, 0) class Base: def __init__(self): self.window = Gtk.Window() self.window.set_resizable(True) self.window.set_title("Draw01") self.window.connect("delete_event", self.delete_event) self.window.connect("show",self.show_event) self.window.set_size_request(gWidth,gHeight) # define the vbox holding all widgets mvbox = Gtk.VBox(homogeneous=False, spacing=5) mvbox.set_border_width(4) self.window.add(mvbox) # define output area marea01 = Gtk.DrawingArea() marea01.connect("draw", self.onDraw) mvbox.pack_start(marea01,True,True,0) # define a label self.msg = Gtk.Label(label='This is a blank area.') mvbox.pack_start(self.msg,False,False,0) # define Next button mbut = Gtk.Button(label="Next") mbut.connect("clicked", self.callback, "actNext") mvbox.pack_start(mbut,False,False,0) self.areaW = 0 self.areaH = 0 self.ScreenNo = 1 self.window.show_all() def show_event(self, widget, data=None): pass def delete_event(self, widget, event, data=None): # quit main program Gtk.main_quit() return False # callback def callback(self, widget, data): if data == 'actNext': self.ScreenNo += 1 if self.ScreenNo==5: self.ScreenNo = 1 # redraw drawing area self.window.queue_draw() # set color def setColor(self, pCr, pColorVec): pCr.set_source_rgb( pColorVec[0]/255.0,pColorVec[1]/255.0,pColorVec[2]/255.0) # shape functions # draw circle # assume the coordinates are given in # screen coordinates def drawCircle(self, pCr, pCentre, pRadius): pCr.arc(pCentre[0], pCentre[1], pRadius, 0, 2*math.pi) pCr.stroke() return True def drawSquare(self, pCr, pCentre, pWidth): pCr.rectangle(pCentre[0]-pWidth/2, \ pCentre[1]-pWidth/2, pWidth, pWidth) pCr.stroke() return True def drawLine(self, pCr, pStart, pEnd): pCr.move_to(pStart[0], pStart[1]) pCr.line_to(pEnd[0], pEnd[1]) pCr.stroke() return True def drawBar(self, pCr, pCentre, pWidth, pHeight): pCr.rectangle(pCentre[0]-pWidth/2, \ pCentre[1]-pHeight, pWidth, pHeight) pCr.stroke() return True # end of shape functions def onDraw(self, pArea, pCr): # get dimensions of the output area self.areaW = pArea.get_allocated_width() self.areaH = pArea.get_allocated_height() # draw black background # ----------------------------------------------------- self.setColor(pCr, gColor_b100) pCr.rectangle(0,0,self.areaW,self.areaH) pCr.fill() # set line properties pCr.set_line_width(2) pCr.set_dash([5.0, 2.0, 2.0, 3.0]) pCr.set_line_cap(cairo.LINE_CAP_BUTT) pCr.set_line_join(cairo.LINE_JOIN_MITER) if self.ScreenNo == 1: # random circles for mI in range(100): mcolor = random.choice( (gColor1,gColor2,gColor3,gColor4)) mr = random.randint(5,60) mX = random.randint(mr+1,self.areaW-mr) mY = random.randint(mr+1,self.areaH-mr) mCentre=(mX,mY) self.setColor(pCr, mcolor) self.drawCircle(pCr, mCentre, mr) self.msg.set_text('Random circles') elif self.ScreenNo == 2: # random lines mX1 = random.randint(1,self.areaW) mY1 = random.randint(1,self.areaH) mStart=(mX1,mY1) for mI in range(100): mcolor = random.choice( (gColor1,gColor2,gColor3,gColor4)) mX2 = random.randint(1,self.areaW) mY2 = random.randint(1,self.areaH) self.setColor(pCr, mcolor) mEnd=(mX2,mY2) self.drawLine(pCr, mStart,mEnd) mStart=(mX2,mY2) self.msg.set_text('Random lines') elif self.ScreenNo == 3: # random bars for mI in range(300): mcolor = random.choice( (gColor1,gColor2,gColor3,gColor4)) mW = 10 mX = random.randint(mW/2,self.areaW-mW/2) mY = random.randint(10,self.areaH-10) mH = random.randint(0,mY-10) mCentre=(mX,mY) self.setColor(pCr, mcolor) self.drawBar(pCr, mCentre, mW, mH) self.msg.set_text('Random bars') elif self.ScreenNo == 4: # random squares for mI in range(300): mcolor = random.choice( (gColor1,gColor2,gColor3,gColor4)) mW = random.randint(5,60) mX = random.randint(int(mW/2),int(self.areaW-mW/2)) mY = random.randint(int(mW/2),int(self.areaH-mW/2)) mCentre=(mX,mY) self.setColor(pCr, mcolor) self.drawSquare(pCr, mCentre, mW) self.msg.set_text('Random squares') def main(): Gtk.main() if __name__ == "__main__": base = Base() main()