ImageTransparencyFixup repairs a particular issue with composing transparent pixels. More...

#include <image_transparency_fixup.h>

Public Member Functions
	ImageTransparencyFixup (QImage *image)
	Create a fixup functor for the given image. More...

void	operator() () const
	Checks all pixels of the image for the known wrong result of composing fully transparent pixels, and replaces them with a fully transparent pixel. More...

Protected Attributes
QRgb *	dest

QRgb *	dest_end

Detailed Description

ImageTransparencyFixup repairs a particular issue with composing transparent pixels.

QPainter::CompositionMode_Multiply and QPainter::CompositionMode_Darken on a QImage of Format_ARGB32_Premultiplied calculate the resulting alpha channel in a very efficient but not accurate way. A particular case is the composition of two fully transparent pixels which should in theory give a fully transparent pixel. Qt yields an alpha value of 1 (in 0..255) instead. The error accumulates with further compositions.

This class may be used as a functor on a particular image, providing a comfortable way to fix the described case after each composition.

Synopsis:

QImage image(100, 100, QImage::Format_ARGB32_Premultiplied); ImageTransparencyFixup fixup(&image); QPainter p(&image); p.setCompositionMode(QPainter::CompositionMode_Multiply); p.drawImage(another_image); p.end(); fixup();

Constructor & Destructor Documentation

◆ ImageTransparencyFixup()

OpenOrienteering::ImageTransparencyFixup::ImageTransparencyFixup ( QImage * image )

inline

Create a fixup functor for the given image.

The image must be of QImage::Format_ARGB32_Premultiplied. It may be null.

Member Function Documentation

◆ operator()()

void OpenOrienteering::ImageTransparencyFixup::operator() ( ) const

inline

Checks all pixels of the image for the known wrong result of composing fully transparent pixels, and replaces them with a fully transparent pixel.

Member Data Documentation

◆ dest

QRgb* OpenOrienteering::ImageTransparencyFixup::dest

protected

◆ dest_end

QRgb* OpenOrienteering::ImageTransparencyFixup::dest_end