public abstract class Gradient

Object
Gradient

ImplementsPaint

Known subtypesConicGradient, LinearGradient, RadialGradient

Abstract description of a CSS-style gradient that can be used as a background or painted directly via Graphics#fillGradient. Three concrete subclasses mirror the corresponding CSS functions:

LinearGradient for linear-gradient(<angle>, <stops>)
RadialGradient for radial-gradient([shape] [extent] [at pos], <stops>)
ConicGradient for conic-gradient([from <angle>] [at pos], <stops>)

A Gradient is a Paint, so it can also be assigned via Graphics#setColor(Paint) and consumed by fillRect / fillShape. The dedicated Graphics#fillGradient(Gradient, int, int, int, int) entry point gives the platform port the rectangle bounds up front so it can pick the fastest native shader path (Java2D LinearGradientPaint / RadialGradientPaint, Android LinearGradient / RadialGradient / SweepGradient, Core Graphics CGGradient).

Subclass instances are intended to be immutable after construction; modify via builder-style setters before handing the gradient off to Graphics or Style. copy() produces a defensive deep clone for places that must outlive caller mutation (e.g. async paint queues).

Fields

`public static final byte KIND_LINEAR = 0`	Sentinel returned by `getKind()` for `LinearGradient` instances.
`public static final byte KIND_RADIAL = 1`	Sentinel returned by `getKind()` for `RadialGradient` instances.
`public static final byte KIND_CONIC = 2`	Sentinel returned by `getKind()` for `ConicGradient` instances.
`public static final byte CYCLE_NONE = 0`	Cycle modes mirroring `MultipleGradientPaint.CycleMethod`.
`public static final byte CYCLE_REPEAT = 1`
`public static final byte CYCLE_REFLECT = 2`

Methods

`public static` `Gradient parseCss(String css)`	Parses a CSS gradient function string and returns the corresponding `Gradient` subclass.
`public abstract byte getKind()`	Returns one of `KIND_LINEAR`, `KIND_RADIAL`, `KIND_CONIC`.
`public final int[] getColors()`	ARGB stop colors (length >= 2).
`public final float[] getPositions()`	Stop positions in [0,1] aligned with `getColors()`.
`public final byte getCycleMethod()`	One of `CYCLE_NONE` / `CYCLE_REPEAT` / `CYCLE_REFLECT`.
`public final` `Gradient setCycleMethod(byte cycleMethod)`	Sets the cycle method.
`public final` `Image getCachedRaster(int width, int height)`	Returns a software-rasterized image of this gradient at the requested rectangle size, reusing a weakly-cached bitmap when possible.
`protected final void invalidateRasterCache()`	Drops the weak cached raster - call after any mutation that changes the painted pixels (cycle method change, subclass parameter change).
`public abstract` `Gradient copy()`	Returns a defensive deep copy.
`public final void paint(Graphics g, Rectangle2D bounds)`	Paints in the given bounds.
`public final void paint(Graphics g, double x, double y, double w, double h)`	Paints in the given bounds.
`public abstract int sampleArgb(int px, int py, int width, int height)`	Software-rasterizer hook used by the default port implementation when no native gradient shader is available.
`protected final int sampleStops(float t)`	Samples one of the stops at fractional position t. Honors the configured cycle method.

Inherited methods

From Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait, clone

Field details

KIND_LINEAR

public static final byte KIND_LINEAR = 0

Sentinel returned by getKind() for LinearGradient instances.

KIND_RADIAL

public static final byte KIND_RADIAL = 1

Sentinel returned by getKind() for RadialGradient instances.

KIND_CONIC

public static final byte KIND_CONIC = 2

Sentinel returned by getKind() for ConicGradient instances.

CYCLE_NONE

public static final byte CYCLE_NONE = 0

Cycle modes mirroring MultipleGradientPaint.CycleMethod. Repeated as byte constants here so that this class (and the .res serializer) does not pull the enum across the resource format boundary.

CYCLE_REPEAT

public static final byte CYCLE_REPEAT = 1

CYCLE_REFLECT

public static final byte CYCLE_REFLECT = 2

Method details

parseCss

public static Gradient parseCss(String css)

Parses a CSS gradient function string and returns the corresponding Gradient subclass. Supports linear-gradient, radial-gradient, conic-gradient, and the repeating-* variants. Mirrors the syntax accepted by the build-time CSS compiler so a string copied verbatim from a .css file produces the same gradient at runtime.

Returns null if css is null/empty or does not look like a gradient function call. Throws IllegalArgumentException on hard parse errors (unknown direction, missing stops, malformed colors).

getKind

public abstract byte getKind()

Returns one of KIND_LINEAR, KIND_RADIAL, KIND_CONIC.

getColors

public final int[] getColors()

ARGB stop colors (length >= 2).

getPositions

public final float[] getPositions()

Stop positions in [0,1] aligned with getColors().

getCycleMethod

public final byte getCycleMethod()

One of CYCLE_NONE / CYCLE_REPEAT / CYCLE_REFLECT. Defaults to NONE.

setCycleMethod

public final Gradient setCycleMethod(byte cycleMethod)

Sets the cycle method. Returns this for chaining.

getCachedRaster

public final Image getCachedRaster(int width, int height)

Returns a software-rasterized image of this gradient at the requested rectangle size, reusing a weakly-cached bitmap when possible. Ports without a hardware shader path can call this from their fillGradient override to avoid re-rasterizing on every frame; the cache is a Display.createSoftWeakRef so the bitmap is reclaimable when idle.

invalidateRasterCache

protected final void invalidateRasterCache()

Drops the weak cached raster - call after any mutation that changes the painted pixels (cycle method change, subclass parameter change). Public so subclass setters can keep the cache coherent.

copy

public abstract Gradient copy()

Returns a defensive deep copy. Implemented by each concrete subclass so async-paint queues can capture an immutable snapshot.

paint

public final void paint(Graphics g, Rectangle2D bounds)

Paints in the given bounds.

Parameters

g Graphics: Graphics context to paint in.
bounds Rectangle2D: Bounds to paint in. User coordinates.

paint

public final void paint(Graphics g, double x, double y, double w, double h)

Paints in the given bounds.

Parameters

g Graphics: Graphics context to paint in.
x double: x coordinate. User space.
y double: y coordinate. USer space.
w double: width. User space.
h double: Hight. User space.

sampleArgb

public abstract int sampleArgb(int px, int py, int width, int height)

Software-rasterizer hook used by the default port implementation when no native gradient shader is available. Samples an ARGB color for the pixel at (px, py) within a rectangle of the given width / height. Ports overriding fillGradient directly do not call this.

sampleStops

protected final int sampleStops(float t)

Samples one of the stops at fractional position t. Honors the configured cycle method. Shared by the three subclasses’ sampling implementations.

CSS repeating-*-gradient stops define one period from positions[0] to positions[last], not [0, 1]. For white 0%, red 16% the period is 0.16 of the gradient extent and the pattern must wrap on that range; collapsing to t - floor(t) would leak the final color across the rest of the rect.