How do I add transparency while creating a pdf using PyFPDF - php

Question

I am using Python version of FPDF, PyFPDF to generate PDFs. I want to add transparency to a rectangle I created using PyFPDF.
I found PHP code in fpdf documentation that lets us add transparency - trasnparency. I tried to follow this and write code in python but it didn't work.
Code snippet found in documentation(in PHP):
source
<?php
require('fpdf.php');
class AlphaPDF extends FPDF
{
var $extgstates = array();
// alpha: real value from 0 (transparent) to 1 (opaque)
// bm: blend mode, one of the following:
// Normal, Multiply, Screen, Overlay, Darken, Lighten, ColorDodge, ColorBurn,
// HardLight, SoftLight, Difference, Exclusion, Hue, Saturation, Color, Luminosity
function SetAlpha($alpha, $bm='Normal')
{
// set alpha for stroking (CA) and non-stroking (ca) operations
$gs = $this->AddExtGState(array('ca'=>$alpha, 'CA'=>$alpha, 'BM'=>'/'.$bm));
$this->SetExtGState($gs);
}
function AddExtGState($parms)
{
$n = count($this->extgstates)+1;
$this->extgstates[$n]['parms'] = $parms;
return $n;
}
function SetExtGState($gs)
{
$this->_out(sprintf('/GS%d gs', $gs));
}
function _enddoc()
{
if(!empty($this->extgstates) && $this->PDFVersion<'1.4')
$this->PDFVersion='1.4';
parent::_enddoc();
}
function _putextgstates()
{
for ($i = 1; $i <= count($this->extgstates); $i++)
{
$this->_newobj();
$this->extgstates[$i]['n'] = $this->n;
$this->_out('<</Type /ExtGState');
$parms = $this->extgstates[$i]['parms'];
$this->_out(sprintf('/ca %.3F', $parms['ca']));
$this->_out(sprintf('/CA %.3F', $parms['CA']));
$this->_out('/BM '.$parms['BM']);
$this->_out('>>');
$this->_out('endobj');
}
}
function _putresourcedict()
{
parent::_putresourcedict();
$this->_out('/ExtGState <<');
foreach($this->extgstates as $k=>$extgstate)
$this->_out('/GS'.$k.' '.$extgstate['n'].' 0 R');
$this->_out('>>');
}
function _putresources()
{
$this->_putextgstates();
parent::_putresources();
}
}
?>
usage
<?php
require('alphapdf.php');
$pdf = new AlphaPDF();
$pdf->AddPage();
$pdf->SetLineWidth(1.5);
// draw opaque red square
$pdf->SetFillColor(255,0,0);
$pdf->Rect(10,10,40,40,'DF');
// set alpha to semi-transparency
$pdf->SetAlpha(0.5);
// draw green square
$pdf->SetFillColor(0,255,0);
$pdf->Rect(20,20,40,40,'DF');
// draw jpeg image
$pdf->Image('lena.jpg',30,30,40);
// restore full opacity
$pdf->SetAlpha(1);
// print name
$pdf->SetFont('Arial', '', 12);
$pdf->Text(46,68,'Lena');
$pdf->Output();
?>
This is what I wrote in python:
source
class EXPDF(FPDF):
def __init__(self, orientation='P', unit='mm', style='A4'):
super(EXPDF, self).__init__(orientation=orientation, unit=unit, format=style)
self.page_format = style.lower()
self.extgstates = {}
def set_alpha(self, alpha, bm='Normal'):
gs = self.add_ext_gstate({'ca': alpha, 'CA': alpha, 'BM': '/'+bm})
self.set_ext_gstate(gs)
def add_ext_gstate(self, parms):
n = len(self.extgstates.keys())+1
if n not in self.extgstates.keys():
self.extgstates[n] = { 'parms': parms }
else:
self.extgstates[n]['parms'] = parms
return n
def set_ext_gstate(self, gs):
self._out(sprintf('/GS%d gs', gs))
def _enddoc(self):
if self.extgstates and self.pdf_version < '1.4':
self.pdf_version = '1.4'
super()._enddoc()
def _putextgstates(self):
for i in range(1, len(self.extgstates.keys())+1):
self._newobj()
self.extgstates[i]['n'] = self.n
self._out('<</Type /ExtGState')
parms = self.extgstates[i]['parms']
self._out(sprintf('/ca %.3F', parms['ca']))
self._out(sprintf('/CA %.3F', parms['CA']))
self._out('/BM'+parms['BM'])
self._out('>>')
self._out('endobj')
def _putresourcedict(self):
super()._putresourcedict()
self._out('/ExtGState <<')
for k in self.extgstates:
self._out('/GS'+str(k)+' '+str(self.extgstates[k]['n'])+' O R')
self._out('>>')
usage
pdf = EXPDF()
pdf.set_alpha(0.5)
pdf.rectangle(20, 20, 40, 40, 'DF')
The code didn't throw any error when I ran it. But when I tried to open the generated pdf in Adobe Acrobat, it said There was a problem reading this document (135). I tried opening the pdf in google chrome. It opened but the rectangle was still opaque.

Answer 1

I think your python code has a couple of errors:
it is missing the _putresources method.
in the method _putresourcesdict the following line has a capital O rather than a zero 0. So change to 0 R.
self._out('/GS'+str(k)+' '+str(self.extgstates[k]['n'])+' O R')

Answer 2

You need a class like this (pyFPDF used https://github.com/reingart/pyfpdf):
class PDF (fpdf.FPDF):
def __init__ (self, orientation = 'P', unit = 'mm', format = 'A4'):
self.__extgstates = []
super().__init__ (orientation, unit, format)
# alpha: real value from 0 (transparent) to 1 (opaque)
# bm: blend mode, one of the following:
# Normal, Multiply, Screen, Overlay, Darken, Lighten, ColorDodge, ColorBurn,
# HardLight, SoftLight, Difference, Exclusion, Hue, Saturation, Color, Luminosity
def set_alpha(self, alpha, bm='Normal'):
# set alpha for stroking (CA) and non-stroking (ca) operations
data = {'ca':alpha,'CA':alpha,'BM':'/' + bm, 'n' : 0}
gs = self.add_ext_gstate(data)
self.set_ext_gstate(gs + 1)
def add_ext_gstate(self, data):
n = len(self.__extgstates)
self.__extgstates.append(data)
return n
def _enddoc(self):
if len(self.__extgstates) > 0 and self.pdf_version < '1.4':
self.pdf_version ='1.4'
super()._enddoc()
def set_ext_gstate(self, gs):
self._out('/GS%d gs' % (gs))
def _putextgstates(self):
i = 0
while i < len(self.__extgstates):
self._newobj()
self._out('<</Type /ExtGState')
self.__extgstates[i]["n"] = self.n
parms = self.__extgstates[i]
self._out('/ca %.3F' % (parms["ca"]))
self._out('/CA %.3F' % (parms["CA"]))
self._out('/BM ' + parms["BM"])
self._out('>>')
self._out('endobj')
i += 1
def _putresourcedict(self):
super()._putresourcedict()
self._out('/ExtGState <<')
for index, eg in enumerate(self.__extgstates):
self._out('/GS' + str(index + 1) + ' ' + str(eg["n"]) + ' 0 R')
self._out('>>')
def _putresources(self):
self._putextgstates()
super()._putresources()