ebiten/blend.go
2022-10-16 22:47:00 +09:00

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// Copyright 2022 The Ebitengine Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ebiten
import (
"fmt"
"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
)
// Blend is a blending way of the source color and the destination color.
//
// The default (zero) value is source-over (regular alpha blending).
type Blend struct {
// BlendFactorSourceColor is a factor for source RGB values.
BlendFactorSourceColor BlendFactor
// BlendFactorSourceAlpha is a factor for source alpha values.
BlendFactorSourceAlpha BlendFactor
// BlendFactorDestinationColor is a factor for destination RGB values.
BlendFactorDestinationColor BlendFactor
// BlendFactorDestinationAlpha is a factor for destination apha values.
BlendFactorDestinationAlpha BlendFactor
// BlendOperationColor is an operation for source and destination RGB values.
BlendOperationColor BlendOperation
// BlendOperationAlpha is an operation for source and destination alpha values.
BlendOperationAlpha BlendOperation
}
func (b Blend) internalBlend() graphicsdriver.Blend {
return graphicsdriver.Blend{
BlendFactorSourceColor: b.BlendFactorSourceColor.internalBlendFactor(true),
BlendFactorSourceAlpha: b.BlendFactorSourceAlpha.internalBlendFactor(true),
BlendFactorDestinationColor: b.BlendFactorDestinationColor.internalBlendFactor(false),
BlendFactorDestinationAlpha: b.BlendFactorDestinationAlpha.internalBlendFactor(false),
BlendOperationColor: b.BlendOperationColor.internalBlendOperation(),
BlendOperationAlpha: b.BlendOperationAlpha.internalBlendOperation(),
}
}
// BlendFactor is a factor for source and destination color values.
type BlendFactor byte
const (
// BlendFactorDefault is the default factor value.
// The actual value depends on which source or destination this value is used.
BlendFactorDefault BlendFactor = iota
BlendFactorZero
BlendFactorOne
BlendFactorSourceAlpha
BlendFactorDestinationAlpha
BlendFactorOneMinusSourceAlpha
BlendFactorOneMinusDestinationAlpha
BlendFactorDestinationColor
)
func (b BlendFactor) internalBlendFactor(source bool) graphicsdriver.BlendFactor {
switch b {
case BlendFactorDefault:
// The default is the source-over composition (regular alpha blending).
if source {
return graphicsdriver.BlendFactorOne
}
return graphicsdriver.BlendFactorOneMinusSourceAlpha
case BlendFactorZero:
return graphicsdriver.BlendFactorZero
case BlendFactorOne:
return graphicsdriver.BlendFactorOne
case BlendFactorSourceAlpha:
return graphicsdriver.BlendFactorSourceAlpha
case BlendFactorDestinationAlpha:
return graphicsdriver.BlendFactorDestinationAlpha
case BlendFactorOneMinusSourceAlpha:
return graphicsdriver.BlendFactorOneMinusSourceAlpha
case BlendFactorOneMinusDestinationAlpha:
return graphicsdriver.BlendFactorOneMinusDestinationAlpha
case BlendFactorDestinationColor:
return graphicsdriver.BlendFactorDestinationColor
default:
panic(fmt.Sprintf("ebiten: invalid blend factor: %d", b))
}
}
// BlendFactor is an operation for source and destination color values.
type BlendOperation byte
const (
// BlendOperationAdd represents adding the source and destination color.
// c_out = factor_src × c_src + factor_dst × c_dst
BlendOperationAdd BlendOperation = iota
)
func (b BlendOperation) internalBlendOperation() graphicsdriver.BlendOperation {
switch b {
case BlendOperationAdd:
return graphicsdriver.BlendOperationAdd
default:
panic(fmt.Sprintf("ebiten: invalid blend operation: %d", b))
}
}
// This name convention follows CSS compositing: https://drafts.fxtf.org/compositing-2/.
//
// 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.
// c_out = c_src + c_dst × (1 - α_src)
BlendSourceOver = Blend{
BlendFactorSourceColor: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,
BlendFactorDestinationColor: BlendFactorOneMinusSourceAlpha,
BlendFactorDestinationAlpha: BlendFactorOneMinusSourceAlpha,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = 0
BlendClear = Blend{
BlendFactorSourceColor: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
BlendFactorDestinationColor: BlendFactorZero,
BlendFactorDestinationAlpha: BlendFactorZero,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src
BlendCopy = Blend{
BlendFactorSourceColor: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,
BlendFactorDestinationColor: BlendFactorZero,
BlendFactorDestinationAlpha: BlendFactorZero,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_dst
BlendDestination = Blend{
BlendFactorSourceColor: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
BlendFactorDestinationColor: BlendFactorOne,
BlendFactorDestinationAlpha: BlendFactorOne,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × (1 - α_dst) + c_dst
BlendDestinationOver = Blend{
BlendFactorSourceColor: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
BlendFactorDestinationColor: BlendFactorOne,
BlendFactorDestinationAlpha: BlendFactorOne,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × α_dst
BlendSourceIn = Blend{
BlendFactorSourceColor: BlendFactorDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorDestinationAlpha,
BlendFactorDestinationColor: BlendFactorZero,
BlendFactorDestinationAlpha: BlendFactorZero,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_dst × α_src
BlendDestinationIn = Blend{
BlendFactorSourceColor: BlendFactorZero,
BlendFactorSourceAlpha: BlendFactorZero,
BlendFactorDestinationColor: BlendFactorSourceAlpha,
BlendFactorDestinationAlpha: BlendFactorSourceAlpha,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × (1 - α_dst)
BlendSourceOut = Blend{
BlendFactorSourceColor: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
BlendFactorDestinationColor: BlendFactorZero,
BlendFactorDestinationAlpha: BlendFactorZero,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_dst × (1 - α_src)
BlendDestinationOut = Blend{
BlendFactorSourceColor: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
BlendFactorDestinationColor: BlendFactorZero,
BlendFactorDestinationAlpha: BlendFactorZero,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × α_dst + c_dst × (1 - α_src)
BlendSourceAtop = Blend{
BlendFactorSourceColor: BlendFactorDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorDestinationAlpha,
BlendFactorDestinationColor: BlendFactorOneMinusSourceAlpha,
BlendFactorDestinationAlpha: BlendFactorOneMinusSourceAlpha,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × (1 - α_dst) + c_dst × α_src
BlendDestinationAtop = Blend{
BlendFactorSourceColor: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
BlendFactorDestinationColor: BlendFactorSourceAlpha,
BlendFactorDestinationAlpha: BlendFactorSourceAlpha,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// c_out = c_src × (1 - α_dst) + c_dst × (1 - α_src)
BlendXor = Blend{
BlendFactorSourceColor: BlendFactorOneMinusDestinationAlpha,
BlendFactorSourceAlpha: BlendFactorOneMinusDestinationAlpha,
BlendFactorDestinationColor: BlendFactorOneMinusSourceAlpha,
BlendFactorDestinationAlpha: BlendFactorOneMinusSourceAlpha,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
// Sum of source and destination (a.k.a. 'plus' or 'additive')
// c_out = c_src + c_dst
BlendLighter = Blend{
BlendFactorSourceColor: BlendFactorOne,
BlendFactorSourceAlpha: BlendFactorOne,
BlendFactorDestinationColor: BlendFactorOne,
BlendFactorDestinationAlpha: BlendFactorOne,
BlendOperationColor: BlendOperationAdd,
BlendOperationAlpha: BlendOperationAdd,
}
)