public final class AlphaComposite extends Object implements Composite
AlphaComposite class implements basic alpha
 compositing rules for combining source and destination colors
 to achieve blending and transparency effects with graphics and
 images.
 The specific rules implemented by this class are the basic set
 of 12 rules described in
 T. Porter and T. Duff, "Compositing Digital Images", SIGGRAPH 84,
 253-259.
 The rest of this documentation assumes some familiarity with the
 definitions and concepts outlined in that paper.
 
 This class extends the standard equations defined by Porter and
 Duff to include one additional factor.
 An instance of the AlphaComposite class can contain
 an alpha value that is used to modify the opacity or coverage of
 every source pixel before it is used in the blending equations.
 
 It is important to note that the equations defined by the Porter
 and Duff paper are all defined to operate on color components
 that are premultiplied by their corresponding alpha components.
 Since the ColorModel and Raster classes
 allow the storage of pixel data in either premultiplied or
 non-premultiplied form, all input data must be normalized into
 premultiplied form before applying the equations and all results
 might need to be adjusted back to the form required by the destination
 before the pixel values are stored.
 
Also note that this class defines only the equations for combining color and alpha values in a purely mathematical sense. The accurate application of its equations depends on the way the data is retrieved from its sources and stored in its destinations. See Implementation Caveats for further information.
The following factors are used in the description of the blending equation in the Porter and Duff paper:
Factor Definition As the alpha component of the source pixel Cs a color component of the source pixel in premultiplied form Ad the alpha component of the destination pixel Cd a color component of the destination pixel in premultiplied form Fs the fraction of the source pixel that contributes to the output Fd the fraction of the destination pixel that contributes to the output Ar the alpha component of the result Cr a color component of the result in premultiplied form 
 Using these factors, Porter and Duff define 12 ways of choosing
 the blending factors Fs and Fd to
 produce each of 12 desirable visual effects.
 The equations for determining Fs and Fd
 are given in the descriptions of the 12 static fields
 that specify visual effects.
 For example,
 the description for
 SRC_OVER
 specifies that Fs = 1 and Fd = (1-As).
 Once a set of equations for determining the blending factors is
 known they can then be applied to each pixel to produce a result
 using the following set of equations:
 
      Fs = f(Ad)
      Fd = f(As)
      Ar = As*Fs + Ad*Fd
      Cr = Cs*Fs + Cd*Fd
 The following factors will be used to discuss our extensions to the blending equation in the Porter and Duff paper:
Factor Definition Csr one of the raw color components of the source pixel Cdr one of the raw color components of the destination pixel Aac the "extra" alpha component from the AlphaComposite instance Asr the raw alpha component of the source pixel Adr the raw alpha component of the destination pixel Adf the final alpha component stored in the destination Cdf the final raw color component stored in the destination 
 The AlphaComposite class defines an additional alpha
 value that is applied to the source alpha.
 This value is applied as if an implicit SRC_IN rule were first
 applied to the source pixel against a pixel with the indicated
 alpha by multiplying both the raw source alpha and the raw
 source colors by the alpha in the AlphaComposite.
 This leads to the following equation for producing the alpha
 used in the Porter and Duff blending equation:
 
      As = Asr * Aac 
 All of the raw source color components need to be multiplied
 by the alpha in the AlphaComposite instance.
 Additionally, if the source was not in premultiplied form
 then the color components also need to be multiplied by the
 source alpha.
 Thus, the equation for producing the source color components
 for the Porter and Duff equation depends on whether the source
 pixels are premultiplied or not:
 
      Cs = Csr * Asr * Aac     (if source is not premultiplied)
      Cs = Csr * Aac           (if source is premultiplied) 
 No adjustment needs to be made to the destination alpha:
 
      Ad = Adr 
 The destination color components need to be adjusted only if they are not in premultiplied form:
      Cd = Cdr * Ad    (if destination is not premultiplied)
      Cd = Cdr         (if destination is premultiplied) 
 The adjusted As, Ad, Cs, and Cd are used in the standard Porter and Duff equations to calculate the blending factors Fs and Fd and then the resulting premultiplied components Ar and Cr.
The results only need to be adjusted if they are to be stored back into a destination buffer that holds data that is not premultiplied, using the following equations:
      Adf = Ar
      Cdf = Cr                 (if dest is premultiplied)
      Cdf = Cr / Ar            (if dest is not premultiplied) 
 Note that since the division is undefined if the resulting alpha
 is zero, the division in that case is omitted to avoid the "divide
 by zero" and the color components are left as
 all zeros.
 
 For performance reasons, it is preferable that
 Raster objects passed to the compose
 method of a CompositeContext object created by the
 AlphaComposite class have premultiplied data.
 If either the source Raster
 or the destination Raster
 is not premultiplied, however,
 appropriate conversions are performed before and after the compositing
 operation.
 
BufferedImage class, do not store alpha values
 for their pixels.  Such sources supply an alpha of 1.0 for
 all of their pixels.
 BufferedImage.TYPE_BYTE_INDEXED
 should not be used as a destination for a blending operation
 because every operation
 can introduce large errors, due to
 the need to choose a pixel from a limited palette to match the
 results of the blending equations.
 Typically the integer values are related to the floating point values in such a way that the integer 0 is equated to the floating point value 0.0 and the integer 2^n-1 (where n is the number of bits in the representation) is equated to 1.0. For 8-bit representations, this means that 0x00 represents 0.0 and 0xff represents 1.0.
    (A, R, G, B) = (0x01, 0xb0, 0x00, 0x00)
 
 If integer math were being used and this value were being
 composited in
 SRC
 mode with no extra alpha, then the math would
 indicate that the results were (in integer format):
 
    (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)
 Note that the intermediate values, which are always in premultiplied form, would only allow the integer red component to be either 0x00 or 0x01. When we try to store this result back into a destination that is not premultiplied, dividing out the alpha will give us very few choices for the non-premultiplied red value. In this case an implementation that performs the math in integer space without shortcuts is likely to end up with the final pixel values of:
    (A, R, G, B) = (0x01, 0xff, 0x00, 0x00)
 (Note that 0x01 divided by 0x01 gives you 1.0, which is equivalent to the value 0xff in an 8-bit storage format.)
Alternately, an implementation that uses floating point math might produce more accurate results and end up returning to the original pixel value with little, if any, roundoff error. Or, an implementation using integer math might decide that since the equations boil down to a virtual NOP on the color values if performed in a floating point space, it can transfer the pixel untouched to the destination and avoid all the math entirely.
These implementations all attempt to honor the same equations, but use different tradeoffs of integer and floating point math and reduced or full equations. To account for such differences, it is probably best to expect only that the premultiplied form of the results to match between implementations and image formats. In this case both answers, expressed in premultiplied form would equate to:
    (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)
 and thus they would all match.
Composite, 
CompositeContext| Modifier and Type | Field and Description | 
|---|---|
| static AlphaComposite | ClearAlphaCompositeobject that implements the opaque CLEAR rule
 with an alpha of 1.0f. | 
| static int | CLEARBoth the color and the alpha of the destination are cleared
 (Porter-Duff Clear rule). | 
| static AlphaComposite | DstAlphaCompositeobject that implements the opaque DST rule
 with an alpha of 1.0f. | 
| static int | DSTThe destination is left untouched
 (Porter-Duff Destination rule). | 
| static int | DST_ATOPThe part of the destination lying inside of the source
 is composited over the source and replaces the destination
 (Porter-Duff Destination Atop Source rule). | 
| static int | DST_INThe part of the destination lying inside of the source
 replaces the destination
 (Porter-Duff Destination In Source rule). | 
| static int | DST_OUTThe part of the destination lying outside of the source
 replaces the destination
 (Porter-Duff Destination Held Out By Source rule). | 
| static int | DST_OVERThe destination is composited over the source and
 the result replaces the destination
 (Porter-Duff Destination Over Source rule). | 
| static AlphaComposite | DstAtopAlphaCompositeobject that implements the opaque DST_ATOP rule
 with an alpha of 1.0f. | 
| static AlphaComposite | DstInAlphaCompositeobject that implements the opaque DST_IN rule
 with an alpha of 1.0f. | 
| static AlphaComposite | DstOutAlphaCompositeobject that implements the opaque DST_OUT rule
 with an alpha of 1.0f. | 
| static AlphaComposite | DstOverAlphaCompositeobject that implements the opaque DST_OVER rule
 with an alpha of 1.0f. | 
| static AlphaComposite | SrcAlphaCompositeobject that implements the opaque SRC rule
 with an alpha of 1.0f. | 
| static int | SRCThe source is copied to the destination
 (Porter-Duff Source rule). | 
| static int | SRC_ATOPThe part of the source lying inside of the destination
 is composited onto the destination
 (Porter-Duff Source Atop Destination rule). | 
| static int | SRC_INThe part of the source lying inside of the destination replaces
 the destination
 (Porter-Duff Source In Destination rule). | 
| static int | SRC_OUTThe part of the source lying outside of the destination
 replaces the destination
 (Porter-Duff Source Held Out By Destination rule). | 
| static int | SRC_OVERThe source is composited over the destination
 (Porter-Duff Source Over Destination rule). | 
| static AlphaComposite | SrcAtopAlphaCompositeobject that implements the opaque SRC_ATOP rule
 with an alpha of 1.0f. | 
| static AlphaComposite | SrcInAlphaCompositeobject that implements the opaque SRC_IN rule
 with an alpha of 1.0f. | 
| static AlphaComposite | SrcOutAlphaCompositeobject that implements the opaque SRC_OUT rule
 with an alpha of 1.0f. | 
| static AlphaComposite | SrcOverAlphaCompositeobject that implements the opaque SRC_OVER rule
 with an alpha of 1.0f. | 
| static AlphaComposite | XorAlphaCompositeobject that implements the opaque XOR rule
 with an alpha of 1.0f. | 
| static int | XORThe part of the source that lies outside of the destination
 is combined with the part of the destination that lies outside
 of the source
 (Porter-Duff Source Xor Destination rule). | 
| Modifier and Type | Method and Description | 
|---|---|
| CompositeContext | createContext(ColorModel srcColorModel,
             ColorModel dstColorModel,
             RenderingHints hints)Creates a context for the compositing operation. | 
| AlphaComposite | derive(float alpha)Returns a similar  AlphaCompositeobject that uses
 the specified alpha value. | 
| AlphaComposite | derive(int rule)Returns a similar  AlphaCompositeobject that uses
 the specified compositing rule. | 
| boolean | equals(Object obj)Determines whether the specified object is equal to this
  AlphaComposite. | 
| float | getAlpha()Returns the alpha value of this  AlphaComposite. | 
| static AlphaComposite | getInstance(int rule)Creates an  AlphaCompositeobject with the specified rule. | 
| static AlphaComposite | getInstance(int rule,
           float alpha)Creates an  AlphaCompositeobject with the specified rule and
 the constant alpha to multiply with the alpha of the source. | 
| int | getRule()Returns the compositing rule of this  AlphaComposite. | 
| int | hashCode()Returns the hashcode for this composite. | 
@Native public static final int CLEAR
Fs = 0 and Fd = 0, thus:
Ar = 0 Cr = 0
@Native public static final int SRC
Fs = 1 and Fd = 0, thus:
Ar = As Cr = Cs
@Native public static final int DST
Fs = 0 and Fd = 1, thus:
Ar = Ad Cr = Cd
@Native public static final int SRC_OVER
Fs = 1 and Fd = (1-As), thus:
Ar = As + Ad*(1-As) Cr = Cs + Cd*(1-As)
@Native public static final int DST_OVER
Fs = (1-Ad) and Fd = 1, thus:
Ar = As*(1-Ad) + Ad Cr = Cs*(1-Ad) + Cd
@Native public static final int SRC_IN
Fs = Ad and Fd = 0, thus:
Ar = As*Ad Cr = Cs*Ad
@Native public static final int DST_IN
Fs = 0 and Fd = As, thus:
Ar = Ad*As Cr = Cd*As
@Native public static final int SRC_OUT
Fs = (1-Ad) and Fd = 0, thus:
Ar = As*(1-Ad) Cr = Cs*(1-Ad)
@Native public static final int DST_OUT
Fs = 0 and Fd = (1-As), thus:
Ar = Ad*(1-As) Cr = Cd*(1-As)
@Native public static final int SRC_ATOP
Fs = Ad and Fd = (1-As), thus:
Ar = As*Ad + Ad*(1-As) = Ad Cr = Cs*Ad + Cd*(1-As)
@Native public static final int DST_ATOP
Fs = (1-Ad) and Fd = As, thus:
Ar = As*(1-Ad) + Ad*As = As Cr = Cs*(1-Ad) + Cd*As
@Native public static final int XOR
Fs = (1-Ad) and Fd = (1-As), thus:
Ar = As*(1-Ad) + Ad*(1-As) Cr = Cs*(1-Ad) + Cd*(1-As)
public static final AlphaComposite Clear
AlphaComposite object that implements the opaque CLEAR rule
 with an alpha of 1.0f.CLEARpublic static final AlphaComposite Src
AlphaComposite object that implements the opaque SRC rule
 with an alpha of 1.0f.SRCpublic static final AlphaComposite Dst
AlphaComposite object that implements the opaque DST rule
 with an alpha of 1.0f.DSTpublic static final AlphaComposite SrcOver
AlphaComposite object that implements the opaque SRC_OVER rule
 with an alpha of 1.0f.SRC_OVERpublic static final AlphaComposite DstOver
AlphaComposite object that implements the opaque DST_OVER rule
 with an alpha of 1.0f.DST_OVERpublic static final AlphaComposite SrcIn
AlphaComposite object that implements the opaque SRC_IN rule
 with an alpha of 1.0f.SRC_INpublic static final AlphaComposite DstIn
AlphaComposite object that implements the opaque DST_IN rule
 with an alpha of 1.0f.DST_INpublic static final AlphaComposite SrcOut
AlphaComposite object that implements the opaque SRC_OUT rule
 with an alpha of 1.0f.SRC_OUTpublic static final AlphaComposite DstOut
AlphaComposite object that implements the opaque DST_OUT rule
 with an alpha of 1.0f.DST_OUTpublic static final AlphaComposite SrcAtop
AlphaComposite object that implements the opaque SRC_ATOP rule
 with an alpha of 1.0f.SRC_ATOPpublic static final AlphaComposite DstAtop
AlphaComposite object that implements the opaque DST_ATOP rule
 with an alpha of 1.0f.DST_ATOPpublic static final AlphaComposite Xor
AlphaComposite object that implements the opaque XOR rule
 with an alpha of 1.0f.XORpublic static AlphaComposite getInstance(int rule)
AlphaComposite object with the specified rule.public static AlphaComposite getInstance(int rule, float alpha)
AlphaComposite object with the specified rule and
 the constant alpha to multiply with the alpha of the source.
 The source is multiplied with the specified alpha before being composited
 with the destination.rule - the compositing rulealpha - the constant alpha to be multiplied with the alpha of
 the source. alpha must be a floating point number in the
 inclusive range [0.0, 1.0].IllegalArgumentException - if
         alpha is less than 0.0 or greater than 1.0, or if
         rule is not one of
         the following:  CLEAR, SRC, DST,
         SRC_OVER, DST_OVER, SRC_IN,
         DST_IN, SRC_OUT, DST_OUT,
         SRC_ATOP, DST_ATOP, or XORpublic CompositeContext createContext(ColorModel srcColorModel, ColorModel dstColorModel, RenderingHints hints)
createContext in interface CompositesrcColorModel - the ColorModel of the sourcedstColorModel - the ColorModel of the destinationhints - the hint that the context object uses to choose between
 rendering alternativesCompositeContext object to be used to perform
 compositing operations.public float getAlpha()
AlphaComposite.  If this
 AlphaComposite does not have an alpha value, 1.0 is returned.AlphaComposite.public int getRule()
AlphaComposite.AlphaComposite.public AlphaComposite derive(int rule)
AlphaComposite object that uses
 the specified compositing rule.
 If this object already uses the specified compositing rule,
 this object is returned.rule - the compositing ruleAlphaComposite object derived from
 this object that uses the specified compositing rule.IllegalArgumentException - if
         rule is not one of
         the following:  CLEAR, SRC, DST,
         SRC_OVER, DST_OVER, SRC_IN,
         DST_IN, SRC_OUT, DST_OUT,
         SRC_ATOP, DST_ATOP, or XORpublic AlphaComposite derive(float alpha)
AlphaComposite object that uses
 the specified alpha value.
 If this object already has the specified alpha value,
 this object is returned.alpha - the constant alpha to be multiplied with the alpha of
 the source. alpha must be a floating point number in the
 inclusive range [0.0, 1.0].AlphaComposite object derived from
 this object that uses the specified alpha value.IllegalArgumentException - if
         alpha is less than 0.0 or greater than 1.0public int hashCode()
hashCode in class ObjectObject.equals(java.lang.Object), 
System.identityHashCode(java.lang.Object)public boolean equals(Object obj)
AlphaComposite.
 
 The result is true if and only if
 the argument is not null and is an
 AlphaComposite object that has the same
 compositing rule and alpha value as this object.
equals in class Objectobj - the Object to test for equalitytrue if obj equals this
 AlphaComposite; false otherwise.Object.hashCode(), 
HashMap Submit a bug or feature 
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