Scaling Operations

To implement image scaling, define slots in your header file to handle the logic:

protected slots:
    void zoomInImage();
    void zoomOutImage();

Connect these slots to your UI actions within the createActions() function:

connect(zoomInAction, &QAction::triggered, this, &ImgProcessor::zoomInImage);
connect(zoomOutAction, &QAction::triggered, this, &ImgProcessor::zoomOutImage);

Implement the scaling logic using the QTransform class (the modern replacement to QMatrix). The following example demonstrates how to apply a scaling factor to the current image:

void ImgProcessor::zoomInImage() {
    if (currentImage.isNull()) return;
    QTransform transform;
    transform.scale(2.0, 2.0);
    currentImage = currentImage.transformed(transform);
    showWidget->imageLabel->setPixmap(QPixmap::fromImage(currentImage));
}

void ImgProcessor::zoomOutImage() {
    if (currentImage.isNull()) return;
    QTransform transform;
    transform.scale(0.5, 0.5);
    currentImage = currentImage.transformed(transform);
    showWidget->imageLabel->setPixmap(QPixmap::fromImage(currentImage));
}

Rotation Logic

To rotate an image, create a slot that applies a transformation matrix with a specified degree value:

void ImgProcessor::rotateImageNinety() {
    if (currentImage.isNull()) return;
    QTransform rotationMatrix;
    rotationMatrix.rotate(90);
    currentImage = currentImage.transformed(rotationMatrix);
    showWidget->imageLabel->setPixmap(QPixmap::fromImage(currentImage));
}

The transformed() method generates a new QImage or QPixmap based on the provided affine trensformation, allowing to non-destructive sequential rotations.

Mirroring Operations

The QImage::mirrored() method simplifies flipping an image horizontally or vertically. Use boolean parameters to control the axis:

void ImgProcessor::flipVertical() {
    if (currentImage.isNull()) return;
    currentImage = currentImage.mirrored(false, true);
    showWidget->imageLabel->setPixmap(QPixmap::fromImage(currentImage));
}

void ImgProcessor::flipHorizontal() {
    if (currentImage.isNull()) return;
    currentImage = currentImage.mirrored(true, false);
    showWidget->imageLabel->setPixmap(QPixmap::fromImage(currentImage));
}

Overview of Transformation Matrices

In Qt, transformation matrices provide a mechanism for coordinate system manipulation, including translation, rotation, scaling, and shearing. While QMatrix is available for legacy 2D support, QTransform is recommended for all new development.

• Translation: matrix.translate(dx, dy) shifts the coordinate system by the specified units.
• Rotation: matrix.rotate(angle) modifies the orientation around the origin.
• Scaling: matrix.scale(sx, sy) multiplies coordinate values to resize the content.
• Shearing: matrix.shear(sh, sv) tilts the coordinates based on horizontal and vertical factors.
• Mapping: Use matrix.map(QPointF) to calculate the new position of a specific point after a transformation has been applied.
• Reset: The reset() function returns the matrix to the identity state, clearing all previous transformations.