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graphics: Add comments to CompositeModes

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Hajime Hoshi 2016-04-14 01:05:50 +09:00
parent 9c508e0444
commit 5f6f2531a9
1 changed files with 41 additions and 14 deletions
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35
graphics.go
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@ -39,19 +39,46 @@ func glFilter(c *opengl.Context, filter Filter) opengl.Filter {
// CompositeMode represents Porter-Duff composition mode. // CompositeMode represents Porter-Duff composition mode.
type CompositeMode int type CompositeMode int
// Note: This name convention follow CSS compositing: https://drafts.fxtf.org/compositing-2/ // This name convention follows CSS compositing: https://drafts.fxtf.org/compositing-2/.
//
// In the above 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.
const ( const (
CompositeModeSourceOver CompositeMode = CompositeMode(opengl.CompositeModeSourceOver) // regular alpha blending // Regular alpha blending
// c_out = c_src + c_dst × (1 - α_src)
CompositeModeSourceOver CompositeMode = CompositeMode(opengl.CompositeModeSourceOver)
// c_out = 0
CompositeModeClear = CompositeMode(opengl.CompositeModeClear) CompositeModeClear = CompositeMode(opengl.CompositeModeClear)
// c_out = c_src
CompositeModeCopy = CompositeMode(opengl.CompositeModeCopy) CompositeModeCopy = CompositeMode(opengl.CompositeModeCopy)
// c_out = c_dst
CompositeModeDestination = CompositeMode(opengl.CompositeModeDestination) CompositeModeDestination = CompositeMode(opengl.CompositeModeDestination)
// c_out = c_src × α_dst
CompositeModeSourceIn = CompositeMode(opengl.CompositeModeSourceIn) CompositeModeSourceIn = CompositeMode(opengl.CompositeModeSourceIn)
// c_out = c_dst × α_src
CompositeModeDestinationIn = CompositeMode(opengl.CompositeModeDestinationIn) CompositeModeDestinationIn = CompositeMode(opengl.CompositeModeDestinationIn)
// c_out = c_src × (1 - α_dst)
CompositeModeSourceOut = CompositeMode(opengl.CompositeModeSourceOut) CompositeModeSourceOut = CompositeMode(opengl.CompositeModeSourceOut)
// c_out = c_dst × (1 - α_src)
CompositeModeDestinationOut = CompositeMode(opengl.CompositeModeDestinationOut) CompositeModeDestinationOut = CompositeMode(opengl.CompositeModeDestinationOut)
// c_out = c_src × α_dst + c_dst × (1 - α_src)
CompositeModeSourceAtop = CompositeMode(opengl.CompositeModeSourceAtop) CompositeModeSourceAtop = CompositeMode(opengl.CompositeModeSourceAtop)
// c_out = c_src × (1 - α_dst) + c_dst × α_src
CompositeModeDestinationAtop = CompositeMode(opengl.CompositeModeDestinationAtop) CompositeModeDestinationAtop = CompositeMode(opengl.CompositeModeDestinationAtop)
// c_out = c_src × (1 - α_dst) + c_dst × (1 - α_src)
CompositeModeXor = CompositeMode(opengl.CompositeModeXor) CompositeModeXor = CompositeMode(opengl.CompositeModeXor)
CompositeModeLighter = CompositeMode(opengl.CompositeModeLighter) // sum of source and destination (a.k.a. 'plus' or 'additive')
// Sum of source and destination (a.k.a. 'plus' or 'additive')
// c_out = c_src + c_dst
CompositeModeLighter = CompositeMode(opengl.CompositeModeLighter)
) )