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ebiten: add documentation about Blend

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Updates #2382
This commit is contained in:
Hajime Hoshi 2022-10-17 11:20:15 +09:00
parent 46a218c278
commit d3b3617f66
1 changed files with 79 additions and 19 deletions
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72
blend.go
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@ -22,7 +22,23 @@ import (
// Blend is a blending way of the source color and the destination color.
//
// The default (zero) value is source-over (regular alpha blending).
// The final color is calculated like this:
//
// c_src: source RGB values
// c_dst: destination RGB values
// c_out: result RGB values
// α_src: source alpha values
// α_dst: destination alpha values
// α_out: result alpha values
//
// c_out = BlendOperationRGB((BlendFactorSourceRGB) × c_src, (BlendFactorDestinationRGB) × c_dst)
// α_out = BlendOperationAlpha((BlendFactorSourceAlpha) × α_src, (BlendFactorDestinationAlpha) × α_dst)
//
// A blend factor is a factor for source and color destination color values.
// The default is source-over (regular alpha blending).
//
// A blend operation is a binary operator of a source color and a destination color.
// The default is adding.
type Blend struct {
// BlendFactorSourceRGB is a factor for source RGB values.
BlendFactorSourceRGB BlendFactor
@ -102,15 +118,21 @@ type BlendOperation byte
const (
// BlendOperationAdd represents adding the source and destination color.
// c_out = factor_src × c_src + factor_dst × c_dst
//
// c_out = (BlendFactorSourceRGB) × c_src + (BlendFactorDestinationRGB) × c_dst
// α_out = (BlendFactorSourceAlpha) × α_src + (BlendFactorDestinationAlpha) × α_dst
BlendOperationAdd BlendOperation = iota
// BlendOperationSubtract represents subtracting the source and destination color.
// c_out = factor_src × c_src - factor_dst × c_dst
//
// c_out = (BlendFactorSourceRGB) × c_src - (BlendFactorDestinationRGB) × c_dst
// α_out = (BlendFactorSourceAlpha) × α_src - (BlendFactorDestinationAlpha) × α_dst
BlendOperationSubtract
// BlendOperationReverseSubtract represents subtracting the source and destination color in a reversed order.
// c_out = factor_dst × c_dst - factor_src × c_src
//
// c_out = (BlendFactorDestinationRGB) × c_dst - (BlendFactorSourceRGB) × c_src
// α_out = (BlendFactorDestinationAlpha) × α_dst - (BlendFactorSourceAlpha) × α_src
BlendOperationReverseSubtract
)
@ -132,8 +154,10 @@ func (b BlendOperation) internalBlendOperation() graphicsdriver.BlendOperation {
// In the comments,
// c_src, c_dst and c_out represent alpha-premultiplied RGB values of source, destination and output respectively. α_src and α_dst represent alpha values of source and destination respectively.
var (
// BlendSourceOver represents the regular alpha blending.
// BlendSourceOver is a preset Blend for the regular alpha blending.
//
// c_out = c_src + c_dst × (1 - α_src)
// α_out = α_src + α_dst × (1 - α_src)
BlendSourceOver = Blend{
BlendFactorSourceRGB: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,
@ -143,7 +167,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendClear is a preset Blend for Porter Duff's 'clear'.
//
// c_out = 0
// α_out = 0
BlendClear = Blend{
BlendFactorSourceRGB: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
@ -153,7 +180,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendCopy is a preset Blend for Porter Duff's 'copy'.
//
// c_out = c_src
// α_out = α_src
BlendCopy = Blend{
BlendFactorSourceRGB: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,
@ -163,7 +193,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendDestination is a preset Blend for Porter Duff's 'destination'.
//
// c_out = c_dst
// α_out = α_dst
BlendDestination = Blend{
BlendFactorSourceRGB: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
@ -173,7 +206,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendDestinationOver is a preset Blend for Porter Duff's 'destination-over'.
//
// c_out = c_src × (1 - α_dst) + c_dst
// α_out = α_src × (1 - α_dst) + α_dst
BlendDestinationOver = Blend{
BlendFactorSourceRGB: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
@ -183,7 +219,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendSourceIn is a preset Blend for Porter Duff's 'source-in'.
//
// c_out = c_src × α_dst
// α_out = α_src × α_dst
BlendSourceIn = Blend{
BlendFactorSourceRGB: BlendFactorDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorDestinationAlpha,
@ -193,7 +232,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendDestinationIn is a preset Blend for Porter Duff's 'destination-in'.
//
// c_out = c_dst × α_src
// α_out = α_dst × α_src
BlendDestinationIn = Blend{
BlendFactorSourceRGB: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
@ -203,7 +245,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendSourceOut is a preset Blend for Porter Duff's 'source-out'.
//
// c_out = c_src × (1 - α_dst)
// α_out = α_src × (1 - α_dst)
BlendSourceOut = Blend{
BlendFactorSourceRGB: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
@ -213,7 +258,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendDestinationOut is a preset Blend for Porter Duff's 'destination-out'.
//
// c_out = c_dst × (1 - α_src)
// α_out = α_dst × (1 - α_src)
BlendDestinationOut = Blend{
BlendFactorSourceRGB: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
@ -223,7 +271,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendSourceAtop is a preset Blend for Porter Duff's 'source-atop'.
//
// c_out = c_src × α_dst + c_dst × (1 - α_src)
// α_out = α_src × α_dst + α_dst × (1 - α_src)
BlendSourceAtop = Blend{
BlendFactorSourceRGB: BlendFactorDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorDestinationAlpha,
@ -233,7 +284,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendDestinationAtop is a preset Blend for Porter Duff's 'destination-atop'.
//
// c_out = c_src × (1 - α_dst) + c_dst × α_src
// α_out = α_src × (1 - α_dst) + α_dst × α_src
BlendDestinationAtop = Blend{
BlendFactorSourceRGB: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
@ -243,7 +297,10 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// BlendXor is a preset Blend for Porter Duff's 'xor'.
//
// c_out = c_src × (1 - α_dst) + c_dst × (1 - α_src)
// α_out = α_src × (1 - α_dst) + α_dst × (1 - α_src)
BlendXor = Blend{
BlendFactorSourceRGB: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
@ -253,8 +310,11 @@ var (
BlendOperationAlpha: BlendOperationAdd,
}
// Sum of source and destination (a.k.a. 'plus' or 'additive')
// BlendLighter is a preset Blend for Porter Duff's 'lighter'.
// This is sum of source and destination (a.k.a. 'plus' or 'additive')
//
// c_out = c_src + c_dst
// α_out = α_src + α_dst
BlendLighter = Blend{
BlendFactorSourceRGB: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,