Trouble with QCursor setting the color of cursor

Question

C++ == language.

QT library.

Using the qt library I am having trouble figuring out exactly how I can go about changing the color of the cursor for my UI with bitmap, or some other means. Any suggestions would be awesome!

Thank you for your time.

Answer 1

To change the cursor shape or even to use custom cursors, QCursor can be used.

It provides a variety of constructors to create cursors in distinct ways:

QCursor::QCursor(const QPixmap &pixmap, int hotX = -1, int hotY = -1)

Constructs a custom pixmap cursor.

pixmap is the image. It is usual to give it a mask (set using QPixmap::setMask()). hotX and hotY define the cursor's hot spot.

If hotX is negative, it is set to the pixmap().width()/2. If hotY is negative, it is set to the pixmap().height()/2.

Valid cursor sizes depend on the display hardware (or the underlying window system). We recommend using 32 x 32 cursors, because this size is supported on all platforms. Some platforms also support 16 x 16, 48 x 48, and 64 x 64 cursors.

See also QPixmap::QPixmap() and QPixmap::setMask() .

---

QCursor::QCursor(const QBitmap &bitmap, const QBitmap &mask, int hotX = -1, int hotY = -1)

Constructs a custom bitmap cursor.

bitmap and mask make up the bitmap. hotX and hotY define the cursor's hot spot.

If hotX is negative, it is set to the bitmap().width()/2. If hotY is negative, it is set to the bitmap().height()/2.

The cursor bitmap (B) and mask (M) bits are combined like this:

• B=1 and M=1 gives black.
• B=0 and M=1 gives white.
• B=0 and M=0 gives transparent.
• B=1 and M=0 gives an XOR'd result under Windows, undefined results on all other platforms.

Use the global Qt color Qt::color0 to draw 0-pixels and Qt::color1 to draw 1-pixels in the bitmaps.

Valid cursor sizes depend on the display hardware (or the underlying window system). We recommend using 32 x 32 cursors, because this size is supported on all platforms. Some platforms also support 16 x 16, 48 x 48, and 64 x 64 cursors.

See also QBitmap::QBitmap() and QBitmap::setMask() .

---

QCursor::QCursor(Qt::CursorShape shape)

Constructs a cursor with the specified shape.

See Qt::CursorShape for a list of shapes.

So, for a colored custom cursor, the constructor with pixmap has to be used.

With QWidget::setCursor() , a custom cursor can be applied to a specific widget.

I prepared an MCVE to demonstrate the various cursor types - testQCursorShape.cc :

// Qt header:
#include <QtWidgets>

// main application
int main(int argc, char **argv)
{
  qDebug() << "Qt Version:" << QT_VERSION_STR;
  QApplication app(argc, argv);
  // setup data
#if 0 // bitmap bits
  const quint32 bitmap[32] = {
    //|0  |4  |8  |12 |16 |20 |24 |28 |32
    0b00000000000000000000000000000000,//- 0
    0b00000000000000000001000000000100,//
    0b00000000000000000011100000001110,//
    0b00000000000000000001110000011100,//
    0b00000000000000000000111000111000,//- 4
    0b00000000000000000000011101110000,//
    0b00000000000000000000001111100000,//
    0b00000000000000000000000111000000,//
    0b00000000000000000000001111100000,//- 8
    0b00000000000000000000011101110000,//
    0b00000000000000000000111000111000,//
    0b00000000000000000001110000011100,//
    0b00000000000000000011100000001110,//- 12
    0b00000000000000000001000000000100,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 16
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 20
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 24
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 28
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
  };
  const quint32 mask[32] = {
    //|0  |4  |8  |12 |16 |20 |24 |28 |32
    0b00000000000000000001000000000100,//- 0
    0b00000000000000000011100000001110,//
    0b00000000000000000111110000011111,//
    0b00000000000000000011111000111110,//
    0b00000000000000000001111101111100,//- 4
    0b00000000000000000000111111111000,//
    0b00000000000000000000011111110000,//
    0b00000000000000000000001111100000,//
    0b00000000000000000000011111110000,//- 8
    0b00000000000000000000111111111000,//
    0b00000000000000000001111101111100,//
    0b00000000000000000011111000111110,//
    0b00000000000000000111110000011111,//- 12
    0b00000000000000000011100000001110,//
    0b00000000000000000001000000000100,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 16
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 20
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 24
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//- 28
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
    0b00000000000000000000000000000000,//
  };
#endif // 0
  const quint32 bitmap[32] = {
    0x00000000,
    0x00001004,
    0x0000380e,
    0x00001c1c,
    0x00000e38,
    0x00000770,
    0x000003e0,
    0x000001c0,
    0x000003e0,
    0x00000770,
    0x00000e38,
    0x00001c1c,
    0x0000380e,
    0x00001004,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
  };
  const quint32 mask[32] = {
    0x00001004,
    0x0000380e,
    0x00007c1f,
    0x00003e3e,
    0x00001f7c,
    0x00000ff8,
    0x000007f0,
    0x000003e0,
    0x000007f0,
    0x00000ff8,
    0x00001f7c,
    0x00003e3e,
    0x00007c1f,
    0x0000380e,
    0x00001004,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
    0x00000000,
  };
  // setup GUI
  // bit map cursor
  const QBitmap qBitmap
    = QBitmap::fromData(QSize(32, 32), (const uchar*)bitmap);
  const QBitmap qBitmapMask
    = QBitmap::fromData(QSize(32, 32), (const uchar*)mask);
  const QCursor qCursorBitmap(qBitmap, qBitmapMask, 7, 7);
  // pixmap cursor
  const QPixmap qPixmap("pencil.png");
  const QCursor qCursorPixmap(qPixmap, 2, 30);
  enum {
    TypeDefault, TypeShape, TypeBitmap, TypePixmap
  };
  // main window
  QWidget qWinMain;
  qWinMain.setWindowTitle(QString::fromUtf8("Test Custom Cursor Shape"));
  QGridLayout qGrid;
  QButtonGroup qTglGrp;
  QRadioButton qTglCursorDefault("Default");
  qTglCursorDefault.setChecked(true);
  qTglGrp.addButton(&qTglCursorDefault, TypeDefault);
  qGrid.addWidget(&qTglCursorDefault, 0, 0);
  QRadioButton qTglCursorShape("Cursor with QCursorShape");
  qTglGrp.addButton(&qTglCursorShape, TypeShape);
  qGrid.addWidget(&qTglCursorShape, 1, 0);
  QRadioButton qTglCursorBitmap("Bitmap Cursor");
  qTglGrp.addButton(&qTglCursorBitmap, TypeBitmap);
  qGrid.addWidget(&qTglCursorBitmap, 2, 0);
  QRadioButton qTglCursorPixmap("Pixmap Cursor");
  qTglGrp.addButton(&qTglCursorPixmap, TypePixmap);
  qGrid.addWidget(&qTglCursorPixmap, 3, 0);
  QFrame qFrmTest;
  qFrmTest.setFrameStyle(QFrame::Panel | QFrame::Sunken);
  qFrmTest.setFixedSize(256, 256);
  qGrid.addWidget(&qFrmTest, 0, 1, 5, 1);
  qWinMain.setLayout(&qGrid);
  // install signal handlers
  QObject::connect(&qTglGrp, QOverload<int>::of(&QButtonGroup::buttonClicked),
    [&](int choice) {
      switch (choice) {
        default:
        case TypeDefault: qFrmTest.unsetCursor(); break;
        case TypeShape: qFrmTest.setCursor(Qt::PointingHandCursor); break;
        case TypeBitmap: qFrmTest.setCursor(qCursorBitmap); break;
        case TypePixmap: qFrmTest.setCursor(qCursorPixmap); break;
      }
    });
  qWinMain.show();
  // runtime loop
  return app.exec();
}

A CMakeLists.txt to prepare VS solution:

project(QCursorShape)

cmake_minimum_required(VERSION 3.10.0)

set_property(GLOBAL PROPERTY USE_FOLDERS ON)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

find_package(Qt5Widgets CONFIG REQUIRED)

include_directories("${CMAKE_SOURCE_DIR}")

add_executable(testQCursorShape testQCursorShape.cc)

target_link_libraries(testQCursorShape Qt5::Widgets)

and the used image file pencil.png which is prepared with an alpha channel (for transparency):

Compiled and tested with VS2017 and Qt 5.13 (on Windows 10):