如何在使用PyFPDF创建pdf时增加透明度

Question

我使用，PyFPDF来生成PDF。我希望向我使用PyFPDF创建的矩形添加透明度。

我在fpdf文档中找到了允许我们添加透明度- 纯种性的PHP代码。我试着遵循这一点，并在python中编写代码，但是它没有工作。

文档中的代码片段(在PHP中)：

源

<?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();
    }
}
?>

使用

<?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();
?>

这就是我在python中所写的：

源

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('>>')

使用

pdf = EXPDF()
pdf.set_alpha(0.5)
pdf.rectangle(20, 20, 40, 40, 'DF')

当我运行它时，代码没有抛出任何错误。但是当我试图打开Acrobat中生成的pdf时，上面写着There was a problem reading this document (135)。我试着在google chrome中打开pdf。它打开了，但矩形仍然是不透明的。

Answer 1

我认为您的python代码有几个错误：

1. 它缺少_putresources方法。
2. 在方法_putresourcesdict中，下面一行的大写字母为O，而不是0。因此，请改为0 R。

self._out('/GS'+str(k)+' '+str(self.extgstates[k]['n'])+' O R')

Answer 2

您需要这样一个类(pyFPDF使用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()