QGraphicsTextItem+trasparent fill+png

[nicolas1]

Hello,
I want to render text item to image file (i.e. png), but keeping background transparent.

QGraphicsScene graphics_scene;
 
    QGraphicsTextItem* text_item;
 
    // some code to add item and set text
 
    text_item->setPos(0, 0);
 
    QRectF source_text_item_rect = text_item->sceneBoundingRect();
 
    QRectF target_text_item_rect;
 
    target_text_item_rect.setX(0);
    target_text_item_rect.setY(0);
    target_text_item_rect.setSize(source_text_item_rect.size());
 
    QPixmap pixmap_with_text(qRound(target_text_item_rect.width()), qRound(target_text_item_rect.height()));
 
    pixmap_with_text.fill(Qt::Transparent);
 
    QPainter pixmap_painter(&pixmap_with_text);
 
    graphics_scene.render(&pixmap_painter, target_text_item_rect, source_text_item_rect);
 
    QString image_with_text_filename; //some filename
 
    return pixmap_with_text.save(image_with_text_filename, "PNG", 100);

QGraphicsScene graphics_scene;

    QGraphicsTextItem* text_item;

    // some code to add item and set text

    text_item->setPos(0, 0);

    QRectF source_text_item_rect = text_item->sceneBoundingRect();

    QRectF target_text_item_rect;

    target_text_item_rect.setX(0);
    target_text_item_rect.setY(0);
    target_text_item_rect.setSize(source_text_item_rect.size());

    QPixmap pixmap_with_text(qRound(target_text_item_rect.width()), qRound(target_text_item_rect.height()));

    pixmap_with_text.fill(Qt::Transparent);

    QPainter pixmap_painter(&pixmap_with_text);

    graphics_scene.render(&pixmap_painter, target_text_item_rect, source_text_item_rect);

    QString image_with_text_filename; //some filename

    return pixmap_with_text.save(image_with_text_filename, "PNG", 100);

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This produce pixmap with only transparent color and no text.

If set fill color to any (non-transparent), then it is filled with that color and with text which is over.

Is it possible to make transparent filling?

[wysota]

You can pass a fourth parameter specifying the value of the alpha channel while constructing a QColor object. I'm not sure why you are using GraphicsView for this, unless the example above is just a big simplification of your true code.

[nicolas1]

text_item->setDefaultTextColor(QColor(0, 0, 255, 255));
//
 
pixmap_with_text.fill(QColor(255, 255, 255, 0));

text_item->setDefaultTextColor(QColor(0, 0, 255, 255));
//

pixmap_with_text.fill(QColor(255, 255, 255, 0));

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