C++ – How to put an QImage with transparency onto the clipboard for another application to use

cqt

I have a QImage that I would like to put on the clipboard, which I can do just fine. However the transparency is lost when that data is pasted into a non-Qt application. The transparent part just comes out as black. I tried saving the data as a transparent PNG but nothing is usable on the clipboard.

This is what I have so far:

QImage mergedImage = mergeSelectedItems(scene->items());

QMimeData* mimeData = new QMimeData();

QByteArray data;
QBuffer buffer(&data);
buffer.open(QIODevice::WriteOnly);
mergedImage.save(&buffer, "PNG");
buffer.close();
mimeData->setData("image/png", data);

clipboard->setMimeData( mimeData );

Best Answer

I had the same problem. I replaced

mimeData->setData("image/png", data);

with

mimeData->setData("PNG", data);

It works in MS Office and Gimp, but not in OpenOffice.

Related Solutions

C++ – How to use the PI constant in C++

On some (especially older) platforms (see the comments below) you might need to

#define _USE_MATH_DEFINES

and then include the necessary header file:

#include <math.h>

and the value of pi can be accessed via:

M_PI

In my math.h (2014) it is defined as:

# define M_PI           3.14159265358979323846  /* pi */

but check your math.h for more. An extract from the "old" math.h (in 2009):

/* Define _USE_MATH_DEFINES before including math.h to expose these macro
 * definitions for common math constants.  These are placed under an #ifdef
 * since these commonly-defined names are not part of the C/C++ standards.
 */

However:

on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the _USE_MATH_DEFINES
On (recent) Linux platforms there are long double values too provided as a GNU Extension:
```
# define M_PIl          3.141592653589793238462643383279502884L /* pi */
```

C++ – How to use range-based for() loop with std::map

Each element of the container is a map<K, V>::value_type, which is a typedef for std::pair<const K, V>. Consequently, in C++17 or higher, you can write

for (auto& [key, value]: myMap) {
    std::cout << key << " has value " << value << std::endl;
}

or as

for (const auto& [key, value]: myMap) {
    std::cout << key << " has value " << value << std::endl;
}

if you don't plan on modifying the values.

In C++11 and C++14, you can use enhanced for loops to extract out each pair on its own, then manually extract the keys and values:

for (const auto& kv : myMap) {
    std::cout << kv.first << " has value " << kv.second << std::endl;
}

You could also consider marking the kv variable const if you want a read-only view of the values.

Best Answer

Related Solutions

C++ – How to use the PI constant in C++

C++ – How to use range-based for() loop with std::map

Related Topic