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

[Israel Brewster]

On Apr 7, 2022, at 12:59 PM, Henry Skoglund <henry at tungware.se> wrote:
> 
> 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 <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++ :-)

Interesting…must be a MacOS thing then. I just tried your C++ code with the exact same results - plain white rectangle. So the only difference I can see now is that you tested on Windows and Linux, while I am testing on MacOS.

Wonderfull. Now I apparently need different code depending on which OS I am running on (assuming I can get this to work on MacOS at all)...
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory 
Geophysical Institute - UAF 
2156 Koyukuk Drive 
Fairbanks AK 99775-7320
Work: 907-474-5172
cell:  907-328-9145

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