[Interest] painter.fillRect() with gradient on PDF printer produces all white?

[Henry Skoglund]

On 2022-04-07 22:04, Israel Brewster wrote:
> On Apr 7, 2022, at 11:58 AM, Henry Skoglund <henry at tungware.se> wrote:
>> On 2022-04-07 20:28, Israel Brewster wrote:
>>> Using Qt 5.15 and PySide2, I am working on a project that requires me to produce a PDF output. My process so far is to create a QWidget containing the content I want, render it to a QPicture (so it won’t be rasterized upon “printing”), then create a PDF QPrinter and use the painter.drawPicture() function to “print” the widget into a PDF.
>>>
>>> This works well, giving me a high-quality vectorized PDF output, with one exception: any item that is filled with a gradient. When printing to PDF, the gradient always comes out as solid white. With some digging, I determined that this is even the case when doing nothing but a simple painter.fillRect() with a gradient.
>>>
>>> Is there any “fix” for this? Thanks.
>>>
>>> If it helps, here is some simple code that reproduces the issue:
>>>
>>> from PySide2.QtWidgets import QApplication
>>> from PySide2.QtGui import QPainter, QPageSize, QLinearGradient
>>> from PySide2.QtPrintSupport import QPrinter
>>> from PySide2.QtCore import QSize, QRect, Qt
>>>
>>> app = QApplication()
>>>
>>> gradient_rect = QRect(0, 0, 500, 25)
>>> gradient = QLinearGradient(0, 0, 1, 0)
>>> gradient.setColorAt(0, Qt.blue)
>>> gradient.setColorAt(1, Qt.red)
>>>
>>> page_size = QPageSize(QSize(500, 25), matchPolicy = QPageSize.ExactMatch)
>>> printer = QPrinter()
>>> printer.setOutputFormat(QPrinter.PdfFormat)
>>> printer.setPageSize(page_size)
>>> printer.setOutputFileName('/tmp/testPDFGradient.pdf')
>>>
>>> painter = QPainter(printer)
>>> painter.fillRect(gradient_rect, gradient)
>>> painter.end()
>>>
>> Hi, try
>> ...
>> gradient_rect = QRect(0, 0, 500, 25)
>> gradient = QLinearGradient(0, 0, 500, 25)
>> gradient.setColorAt(0, Qt.blue)
>> gradient.setColorAt(1, Qt.red)
>> ...
>> (i.e. QLinearGradient's ctor expects coords)
> No change. The 1 value was picked because that’s what displays correctly in testing, but even with the suggested change I still get a solid white box.
>
Hmm, I just tested on Ubuntu 20.04, created an empty vanilla widget 
program in Qt 5.15.2. added "printsupport" to the .pro file and changed 
mainwindow.cpp to look like this:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QtPrintSupport"

MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)
     , ui(new Ui::MainWindow)
{
     ui->setupUi(this);

     auto gradient_rect = QRect(0,0,500,25);
     auto gradient = QLinearGradient(0,0,500,25);
     gradient.setColorAt(0,Qt::blue);
     gradient.setColorAt(1,Qt::red);

     QPrinter printer;
     QPageSize ps(QSize(500,25),"GradientTest",QPageSize::ExactMatch);
     printer.setOutputFormat(QPrinter::PdfFormat);
     printer.setPageSize(ps);
printer.setOutputFileName("/home/henry/Downloads/testPDFGradient.pdf");

     QPainter painter;
     painter.begin(&printer);
     painter.fillRect(gradient_rect,gradient);
     painter.end();
}

MainWindow::~MainWindow()
{
     delete ui;
}

screenshot here: https://tungware.se/GradientOnUbuntu.png
(also tested on Windows 10 MSVC2019 Qt 5.15.2 and works there as well)

Maybe pySide2 messes up something, you could try with some C++ :-)