digiKam Developer Documentation
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Digikam::DColorComposer Class Referenceabstract
+ Inheritance diagram for Digikam::DColorComposer:

Public Types

enum  CompositingOperation {
  PorterDuffNone , PorterDuffClear , PorterDuffSrc , PorterDuffSrcOver ,
  PorterDuffDstOver , PorterDuffSrcIn , PorterDuffDstIn , PorterDuffSrcOut ,
  PorterDuffDstOut , PorterDuffSrcAtop , PorterDuffDstAtop , PorterDuffXor
}
 The available rules to combine src and destination color. More...
 
enum  MultiplicationFlags {
  NoMultiplication = 0x00 , PremultiplySrc = 0x01 , PremultiplyDst = 0x02 , DemultiplyDst = 0x04 ,
  MultiplicationFlagsDImg = PremultiplySrc | PremultiplyDst | DemultiplyDst , MultiplicationFlagsPremultipliedColorOnDImg = PremultiplyDst | DemultiplyDst
}
 

Public Member Functions

virtual void compose (DColor &dest, DColor &src)=0
 Carry out the actual composition process.
 
virtual void compose (DColor &dest, DColor &src, MultiplicationFlags multiplicationFlags)
 Compose the two colors by calling compose(dest, src).
 

Static Public Member Functions

static DColorComposergetComposer (CompositingOperation rule)
 Retrieve a DColorComposer object for one of the predefined rules.
 

Member Enumeration Documentation

◆ CompositingOperation

For the Porter-Duff rules, the formula is component = (source * fs + destination * fd) where fs, fd according to the following table with sa = source alpha, da = destination alpha:

None fs: sa fd: 1.0-sa Clear fs: 0.0 fd: 0.0 Src fs: 1.0 fd: 0.0 Src Over fs: 1.0 fd: 1.0-sa Dst Over fs: 1.0-da fd: 1.0 Src In fs: da fd: 0.0 Dst In fs: 0.0 fd: sa Src Out fs: 1.0-da fd: 0.0 Dst Out fs: 0.0 fd: 1.0-sa

Src Atop fs: da fd: 1.0-sa Dst Atop fs: 1.0-da fd: sa Xor fs: 1.0-da fd: 1.0-sa

None is the default, classical blending mode, a "Src over" simplification: Blend non-premultiplied RGBA data "src over" a fully opaque background. Src is the painter's algorithm. All other operations require premultiplied colors. The documentation of java.awt.AlphaComposite (Java 1.5) provides a good introduction and documentation on Porter Duff.

Member Function Documentation

◆ compose() [1/2]

virtual void Digikam::DColorComposer::compose ( DColor dest,
DColor src 
)
pure virtual

Src and Dest are composed and the result is written to dest. No pre-/demultiplication is done by this method, use the other overloaded methods, which call this method, if you need pre- or demultiplication (you need it if any of the colors are read from or written to a DImg).

If you just pass the object to a DImg method, you do not need to call this. Call this function if you want to compose two colors. Implement this function if you create a custom DColorComposer.

The bit depth of source and destination color must be identical.

◆ compose() [2/2]

void Digikam::DColorComposer::compose ( DColor dest,
DColor src,
DColorComposer::MultiplicationFlags  multiplicationFlags 
)
virtual

Pre- and demultiplication operations are done as specified. For PorterDuff operations except PorterDuffNone, you need

  • PremultiplySrc if src is not premultiplied (read from a DImg)
  • PremultiplyDst if dst is not premultiplied (read from a DImg)
  • DemultiplyDst if dst will be written to non-premultiplied data (a DImg)

◆ getComposer()

DColorComposer * Digikam::DColorComposer::getComposer ( DColorComposer::CompositingOperation  rule)
static

The object needs to be deleted by the caller.