| SkBlendMode Overview |
| === |
| Describes how destination <a href='undocumented#Pixel'>pixel</a> is replaced with a combination of itself and |
| source <a href='undocumented#Pixel'>pixel</a>. <a href='#Blend_Mode'>Blend_Mode</a> may use source, destination, or both. <a href='#Blend_Mode'>Blend_Mode</a> may |
| operate on each <a href='SkColor_Reference#Color'>Color</a> component independently, or may allow all source <a href='undocumented#Pixel'>pixel</a> |
| components to contribute to one destination <a href='undocumented#Pixel'>pixel</a> component. |
| |
| <a href='#Blend_Mode'>Blend_Mode</a> does not use adjacent pixels to determine the outcome. |
| |
| <a href='#Blend_Mode'>Blend_Mode</a> uses source and read destination <a href='SkColor_Reference#Alpha'>Alpha</a> to determine written |
| destination <a href='SkColor_Reference#Alpha'>Alpha</a>; both source and destination <a href='SkColor_Reference#Alpha'>Alpha</a> may also affect written |
| destination <a href='SkColor_Reference#Color'>Color</a> components. |
| |
| Regardless of how <a href='SkColor_Reference#Alpha'>Alpha</a> is encoded in source and destination <a href='undocumented#Pixel'>pixel</a>, nearly all |
| <a href='#Image_Info_Color_Type'>Color_Types</a> treat it as ranging from zero to one. And, nearly all <a href='#Blend_Mode'>Blend_Mode</a> |
| algorithms limit the output so that all results are also zero to one. |
| |
| Two exceptions are <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kPlus'>kPlus</a> and <a href='SkImageInfo_Reference#kRGBA_F16_SkColorType'>kRGBA_F16_SkColorType</a>. |
| |
| <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kPlus'>kPlus</a> permits computing <a href='SkColor_Reference#Alpha'>Alpha</a> and <a href='SkColor_Reference#Color'>Color</a> component values larger |
| than one. For <a href='#Image_Info_Color_Type'>Color_Types</a> other than <a href='SkImageInfo_Reference#kRGBA_F16_SkColorType'>kRGBA_F16_SkColorType</a>, resulting <a href='SkColor_Reference#Alpha'>Alpha</a> |
| and component values are clamped to one. |
| |
| <a href='SkImageInfo_Reference#kRGBA_F16_SkColorType'>kRGBA_F16_SkColorType</a> permits values outside the zero to one range. It is up |
| to the client to ensure that the result is within the range of zero to one, |
| and therefore well-defined. |
| |
| <a name='Porter_Duff'></a> |
| |
| <a href='https://graphics.pixar.com/library/Compositing/paper.pdf'>Compositing Digital Images</a></a> describes <a href='#Blend_Mode_Overview_Porter_Duff'>Porter_Duff</a> modes <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kClear'>kClear</a> through <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kXor'>kXor</a>. |
| |
| Drawing a <a href='SkBitmap_Reference#Bitmap'>bitmap</a> with transparency using <a href='#Blend_Mode_Overview_Porter_Duff'>Porter_Duff</a> compositing is free to clear |
| the destination. |
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|  |
| |
| Draw geometry with transparency using <a href='#Blend_Mode_Overview_Porter_Duff'>Porter_Duff</a> compositing does not combine |
| transparent source pixels, leaving the destination outside the geometry untouched. |
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|  |
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| <a name='Lighten_Darken'></a> |
| |
| Modes <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kPlus'>kPlus</a> and <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kScreen'>kScreen</a> use |
| simple arithmetic to lighten or darken the destination. Modes |
| <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kOverlay'>kOverlay</a> through <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kMultiply'>kMultiply</a> use more complicated |
| algorithms to lighten or darken; sometimes one mode does both, as described by |
| <a href='https://en.wikipedia.org/wiki/Blend_modes'>Blend Modes</a></a> . |
| |
|  |
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| <a name='Modulate_Blend'></a> |
| |
| <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kModulate'>kModulate</a> is a mashup of <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kSrcATop'>kSrcATop</a> and <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kMultiply'>kMultiply</a>. |
| It multiplies all components, including <a href='SkColor_Reference#Alpha'>Alpha</a>; unlike <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kMultiply'>kMultiply</a>, if either |
| source or destination is transparent, result is transparent. <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kModulate'>kModulate</a> |
| uses <a href='undocumented#Premultiply'>Premultiplied</a> values to compute the product; <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kMultiply'>kMultiply</a> uses <a href='undocumented#Unpremultiply'>Unpremultiplied</a> |
| values to compute the product. |
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|  |
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| <a name='Color_Blends'></a> |
| |
| Modes <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kHue'>kHue</a>, <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kSaturation'>kSaturation</a>, <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kColor'>kColor</a>, and |
| <a href='SkBlendMode_Reference#SkBlendMode'>SkBlendMode</a>::<a href='#SkBlendMode_kLuminosity'>kLuminosity</a> convert source and destination pixels using all |
| components <a href='SkColor_Reference#Color'>color</a> information, using |
| <a href='https://www.w3.org/TR/compositing-1/#blendingnonseparable'>non-separable blend modes</a></a> . |
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|  |
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