/* | |

* Copyright 2006 The Android Open Source Project | |

* | |

* Use of this source code is governed by a BSD-style license that can be | |

* found in the LICENSE file. | |

*/ | |

#ifndef SkGradientShader_DEFINED | |

#define SkGradientShader_DEFINED | |

#include "include/core/SkColorSpace.h" | |

#include "include/core/SkRefCnt.h" | |

#include "include/core/SkShader.h" | |

#include "include/core/SkTileMode.h" | |

/** \class SkGradientShader | |

SkGradientShader hosts factories for creating subclasses of SkShader that | |

render linear and radial gradients. In general, degenerate cases should not | |

produce surprising results, but there are several types of degeneracies: | |

* A linear gradient made from the same two points. | |

* A radial gradient with a radius of zero. | |

* A sweep gradient where the start and end angle are the same. | |

* A two point conical gradient where the two centers and the two radii are | |

the same. | |

For any degenerate gradient with a decal tile mode, it will draw empty since the interpolating | |

region is zero area and the outer region is discarded by the decal mode. | |

For any degenerate gradient with a repeat or mirror tile mode, it will draw a solid color that | |

is the average gradient color, since infinitely many repetitions of the gradients will fill the | |

shape. | |

For a clamped gradient, every type is well-defined at the limit except for linear gradients. The | |

radial gradient with zero radius becomes the last color. The sweep gradient draws the sector | |

from 0 to the provided angle with the first color, with a hardstop switching to the last color. | |

When the provided angle is 0, this is just the solid last color again. Similarly, the two point | |

conical gradient becomes a circle filled with the first color, sized to the provided radius, | |

with a hardstop switching to the last color. When the two radii are both zero, this is just the | |

solid last color. | |

As a linear gradient approaches the degenerate case, its shader will approach the appearance of | |

two half planes, each filled by the first and last colors of the gradient. The planes will be | |

oriented perpendicular to the vector between the two defining points of the gradient. However, | |

once they become the same point, Skia cannot reconstruct what that expected orientation is. To | |

provide a stable and predictable color in this case, Skia just uses the last color as a solid | |

fill to be similar to many of the other degenerate gradients' behaviors in clamp mode. | |

*/ | |

class SK_API SkGradientShader { | |

public: | |

enum Flags { | |

/** By default gradients will interpolate their colors in unpremul space | |

* and then premultiply each of the results. By setting this flag, the | |

* gradients will premultiply their colors first, and then interpolate | |

* between them. | |

* example: https://fiddle.skia.org/c/@GradientShader_MakeLinear | |

*/ | |

kInterpolateColorsInPremul_Flag = 1 << 0, | |

}; | |

struct Interpolation { | |

enum class InPremul : bool { kNo = false, kYes = true }; | |

enum class ColorSpace : uint8_t { | |

// Default Skia behavior: interpolate in the color space of the destination surface | |

kDestination, | |

// https://www.w3.org/TR/css-color-4/#interpolation-space | |

kSRGBLinear, | |

kLab, | |

kOKLab, | |

kLCH, | |

kOKLCH, | |

kSRGB, | |

kHSL, | |

kHWB, | |

kLastColorSpace = kHWB, | |

}; | |

static constexpr int kColorSpaceCount = static_cast<int>(ColorSpace::kLastColorSpace) + 1; | |

enum class HueMethod : uint8_t { | |

// https://www.w3.org/TR/css-color-4/#hue-interpolation | |

kShorter, | |

kLonger, | |

kIncreasing, | |

kDecreasing, | |

kLastHueMethod = kDecreasing, | |

}; | |

static constexpr int kHueMethodCount = static_cast<int>(HueMethod::kLastHueMethod) + 1; | |

InPremul fInPremul = InPremul::kNo; | |

/* | |

* NOTE: Do not use fColorSpace or fHueMethod (yet). These features are in development and | |

* incomplete. This comment (and RELEASE_NOTES.txt) will be updated once the features are | |

* ready to be used. | |

*/ | |

ColorSpace fColorSpace = ColorSpace::kDestination; | |

HueMethod fHueMethod = HueMethod::kShorter; // Only relevant for LCH, OKLCH, HSL, or HWB | |

static Interpolation FromFlags(uint32_t flags) { | |

return {flags & kInterpolateColorsInPremul_Flag ? InPremul::kYes : InPremul::kNo, | |

ColorSpace::kDestination, | |

HueMethod::kShorter}; | |

} | |

}; | |

/** Returns a shader that generates a linear gradient between the two specified points. | |

<p /> | |

@param pts The start and end points for the gradient. | |

@param colors The array[count] of colors, to be distributed between the two points | |

@param pos May be NULL. array[count] of SkScalars, or NULL, of the relative position of | |

each corresponding color in the colors array. If this is NULL, | |

the the colors are distributed evenly between the start and end point. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >=2. The number of colors (and pos if not NULL) entries. | |

@param mode The tiling mode | |

example: https://fiddle.skia.org/c/@GradientShader_MakeLinear | |

*/ | |

static sk_sp<SkShader> MakeLinear(const SkPoint pts[2], | |

const SkColor colors[], const SkScalar pos[], int count, | |

SkTileMode mode, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr); | |

/** Returns a shader that generates a linear gradient between the two specified points. | |

<p /> | |

@param pts The start and end points for the gradient. | |

@param colors The array[count] of colors, to be distributed between the two points | |

@param pos May be NULL. array[count] of SkScalars, or NULL, of the relative position of | |

each corresponding color in the colors array. If this is NULL, | |

the the colors are distributed evenly between the start and end point. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >=2. The number of colors (and pos if not NULL) entries. | |

@param mode The tiling mode | |

example: https://fiddle.skia.org/c/@GradientShader_MakeLinear | |

*/ | |

static sk_sp<SkShader> MakeLinear(const SkPoint pts[2], | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, SkTileMode mode, | |

const Interpolation& interpolation, | |

const SkMatrix* localMatrix); | |

static sk_sp<SkShader> MakeLinear(const SkPoint pts[2], | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, SkTileMode mode, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr) { | |

return MakeLinear(pts, colors, std::move(colorSpace), pos, count, mode, | |

Interpolation::FromFlags(flags), localMatrix); | |

} | |

/** Returns a shader that generates a radial gradient given the center and radius. | |

<p /> | |

@param center The center of the circle for this gradient | |

@param radius Must be positive. The radius of the circle for this gradient | |

@param colors The array[count] of colors, to be distributed between the center and edge of the circle | |

@param pos May be NULL. The array[count] of SkScalars, or NULL, of the relative position of | |

each corresponding color in the colors array. If this is NULL, | |

the the colors are distributed evenly between the center and edge of the circle. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >= 2. The number of colors (and pos if not NULL) entries | |

@param mode The tiling mode | |

*/ | |

static sk_sp<SkShader> MakeRadial(const SkPoint& center, SkScalar radius, | |

const SkColor colors[], const SkScalar pos[], int count, | |

SkTileMode mode, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr); | |

/** Returns a shader that generates a radial gradient given the center and radius. | |

<p /> | |

@param center The center of the circle for this gradient | |

@param radius Must be positive. The radius of the circle for this gradient | |

@param colors The array[count] of colors, to be distributed between the center and edge of the circle | |

@param pos May be NULL. The array[count] of SkScalars, or NULL, of the relative position of | |

each corresponding color in the colors array. If this is NULL, | |

the the colors are distributed evenly between the center and edge of the circle. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >= 2. The number of colors (and pos if not NULL) entries | |

@param mode The tiling mode | |

*/ | |

static sk_sp<SkShader> MakeRadial(const SkPoint& center, SkScalar radius, | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, SkTileMode mode, | |

const Interpolation& interpolation, | |

const SkMatrix* localMatrix); | |

static sk_sp<SkShader> MakeRadial(const SkPoint& center, SkScalar radius, | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, SkTileMode mode, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr) { | |

return MakeRadial(center, radius, colors, std::move(colorSpace), pos, count, mode, | |

Interpolation::FromFlags(flags), localMatrix); | |

} | |

/** | |

* Returns a shader that generates a conical gradient given two circles, or | |

* returns NULL if the inputs are invalid. The gradient interprets the | |

* two circles according to the following HTML spec. | |

* http://dev.w3.org/html5/2dcontext/#dom-context-2d-createradialgradient | |

*/ | |

static sk_sp<SkShader> MakeTwoPointConical(const SkPoint& start, SkScalar startRadius, | |

const SkPoint& end, SkScalar endRadius, | |

const SkColor colors[], const SkScalar pos[], | |

int count, SkTileMode mode, | |

uint32_t flags = 0, | |

const SkMatrix* localMatrix = nullptr); | |

/** | |

* Returns a shader that generates a conical gradient given two circles, or | |

* returns NULL if the inputs are invalid. The gradient interprets the | |

* two circles according to the following HTML spec. | |

* http://dev.w3.org/html5/2dcontext/#dom-context-2d-createradialgradient | |

*/ | |

static sk_sp<SkShader> MakeTwoPointConical(const SkPoint& start, SkScalar startRadius, | |

const SkPoint& end, SkScalar endRadius, | |

const SkColor4f colors[], | |

sk_sp<SkColorSpace> colorSpace, const SkScalar pos[], | |

int count, SkTileMode mode, | |

const Interpolation& interpolation, | |

const SkMatrix* localMatrix); | |

static sk_sp<SkShader> MakeTwoPointConical(const SkPoint& start, SkScalar startRadius, | |

const SkPoint& end, SkScalar endRadius, | |

const SkColor4f colors[], | |

sk_sp<SkColorSpace> colorSpace, const SkScalar pos[], | |

int count, SkTileMode mode, | |

uint32_t flags = 0, | |

const SkMatrix* localMatrix = nullptr) { | |

return MakeTwoPointConical(start, startRadius, end, endRadius, colors, | |

std::move(colorSpace), pos, count, mode, | |

Interpolation::FromFlags(flags), localMatrix); | |

} | |

/** Returns a shader that generates a sweep gradient given a center. | |

The shader accepts negative angles and angles larger than 360, draws | |

between 0 and 360 degrees, similar to the CSS conic-gradient | |

semantics. 0 degrees means horizontal positive x axis. The start angle | |

must be less than the end angle, otherwise a null pointer is | |

returned. If color stops do not contain 0 and 1 but are within this | |

range, the respective outer color stop is repeated for 0 and 1. Color | |

stops less than 0 are clamped to 0, and greater than 1 are clamped to 1. | |

<p /> | |

@param cx The X coordinate of the center of the sweep | |

@param cx The Y coordinate of the center of the sweep | |

@param colors The array[count] of colors, to be distributed around the center, within | |

the gradient angle range. | |

@param pos May be NULL. The array[count] of SkScalars, or NULL, of the relative | |

position of each corresponding color in the colors array. If this is | |

NULL, then the colors are distributed evenly within the angular range. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >= 2. The number of colors (and pos if not NULL) entries | |

@param mode Tiling mode: controls drawing outside of the gradient angular range. | |

@param startAngle Start of the angular range, corresponding to pos == 0. | |

@param endAngle End of the angular range, corresponding to pos == 1. | |

*/ | |

static sk_sp<SkShader> MakeSweep(SkScalar cx, SkScalar cy, | |

const SkColor colors[], const SkScalar pos[], int count, | |

SkTileMode mode, | |

SkScalar startAngle, SkScalar endAngle, | |

uint32_t flags, const SkMatrix* localMatrix); | |

static sk_sp<SkShader> MakeSweep(SkScalar cx, SkScalar cy, | |

const SkColor colors[], const SkScalar pos[], int count, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr) { | |

return MakeSweep(cx, cy, colors, pos, count, SkTileMode::kClamp, 0, 360, flags, | |

localMatrix); | |

} | |

/** Returns a shader that generates a sweep gradient given a center. | |

The shader accepts negative angles and angles larger than 360, draws | |

between 0 and 360 degrees, similar to the CSS conic-gradient | |

semantics. 0 degrees means horizontal positive x axis. The start angle | |

must be less than the end angle, otherwise a null pointer is | |

returned. If color stops do not contain 0 and 1 but are within this | |

range, the respective outer color stop is repeated for 0 and 1. Color | |

stops less than 0 are clamped to 0, and greater than 1 are clamped to 1. | |

<p /> | |

@param cx The X coordinate of the center of the sweep | |

@param cx The Y coordinate of the center of the sweep | |

@param colors The array[count] of colors, to be distributed around the center, within | |

the gradient angle range. | |

@param pos May be NULL. The array[count] of SkScalars, or NULL, of the relative | |

position of each corresponding color in the colors array. If this is | |

NULL, then the colors are distributed evenly within the angular range. | |

If this is not null, the values must lie between 0.0 and 1.0, and be | |

strictly increasing. If the first value is not 0.0, then an additional | |

color stop is added at position 0.0, with the same color as colors[0]. | |

If the the last value is not 1.0, then an additional color stop is added | |

at position 1.0, with the same color as colors[count - 1]. | |

@param count Must be >= 2. The number of colors (and pos if not NULL) entries | |

@param mode Tiling mode: controls drawing outside of the gradient angular range. | |

@param startAngle Start of the angular range, corresponding to pos == 0. | |

@param endAngle End of the angular range, corresponding to pos == 1. | |

*/ | |

static sk_sp<SkShader> MakeSweep(SkScalar cx, SkScalar cy, | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, | |

SkTileMode mode, | |

SkScalar startAngle, SkScalar endAngle, | |

const Interpolation& interpolation, | |

const SkMatrix* localMatrix); | |

static sk_sp<SkShader> MakeSweep(SkScalar cx, SkScalar cy, | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, | |

SkTileMode mode, | |

SkScalar startAngle, SkScalar endAngle, | |

uint32_t flags, const SkMatrix* localMatrix) { | |

return MakeSweep(cx, cy, colors, std::move(colorSpace), pos, count, mode, startAngle, | |

endAngle, Interpolation::FromFlags(flags), localMatrix); | |

} | |

static sk_sp<SkShader> MakeSweep(SkScalar cx, SkScalar cy, | |

const SkColor4f colors[], sk_sp<SkColorSpace> colorSpace, | |

const SkScalar pos[], int count, | |

uint32_t flags = 0, const SkMatrix* localMatrix = nullptr) { | |

return MakeSweep(cx, cy, colors, std::move(colorSpace), pos, count, SkTileMode::kClamp, | |

0, 360, flags, localMatrix); | |

} | |

}; | |

#endif |