Nicolas Cellier uploaded a new version of Graphics to project The Trunk:
http://source.squeak.org/trunk/Graphics-nice.540.mcz

==================== Summary ====================

Name: Graphics-nice.540
Author: nice
Time: 27 February 2023, 11:08:20.503071 pm
UUID: 3ed34a8a-0e5a-9044-a70b-de82186f7a48
Ancestors: Graphics-nice.539

Fix load of interlaced PNG again :

we must use rule 31 (Form paintAlpha) which does the right thing:
- use destinationPixel when sourcePixel is zero
- else use sourcePixel

This is because the default constant sourceAlpha used for blending is 255, and rule 31 perform this pseudo code for each A,R,G,B channel:

    (sourceChannel * sourceAlpha) + (destinationChannel * (255 - sourceAlpha)) / 255

    which is = sourceChannel.

=============== Diff against Graphics-nice.539 ===============

Item was changed:
  ----- Method: PNGReadWriter>>copyPixelsRGB:at:by: (in category 'pixel copies') -----
  copyPixelsRGB: y at: startX by: incX
  	"Handle interlaced RGB color mode (colorType = 2)"
  
  	| i pixel tempForm tempBits xx loopsToDo |
  
  	tempForm := Form extent: width at 1 depth: 32.
  	tempBits := tempForm bits.
  	pixel := LargePositiveInteger new: 4.
  	pixel at: 4 put: 16rFF.
  	loopsToDo := width - startX + incX - 1 // incX.
  	bitsPerChannel = 8
  		ifTrue:
  			[i := (startX // incX * 3) + 1.
  			xx := startX+1.
  			1 to: loopsToDo do:
  				[ :j |
  				pixel
  					at: 3 put: (thisScanline at: i);
  					at: 2 put: (thisScanline at: i+1);
  					at: 1 put: (thisScanline at: i+2).
  				tempBits at: xx put: pixel normalize.
  				i := i + 3.
  				xx := xx + incX].
  			transparentPixelValue
  				ifNotNil: [startX to: width-1 by: incX do: [ :x |
  					(tempBits at: x+1) = transparentPixelValue
  						ifTrue: [	tempBits at: x+1 put: 0]]]]
  		ifFalse:
  			[i := (startX // incX * 6) + 1.
  			xx := startX+1.
  			1 to: loopsToDo do:
  				[ :j |
  				(transparentPixelValue == nil or: [(1 to: 6) anySatisfy: [:k | (transparentPixelValue digitAt: k) ~= (thisScanline at: i + 6 - k)]])
  					ifTrue:
  						[pixel
  							at: 3 put: (thisScanline at: i);
  							at: 2 put: (thisScanline at: i+2);
  							at: 1 put: (thisScanline at: i+4).
  						tempBits at: xx put: pixel normalize.]
  					ifFalse:
  						[tempBits at: xx put: 0].
  				i := i + 6.
  				xx := xx + incX]].
+ 	tempForm displayOn: form at: 0 at y rule: Form paintAlpha
- 	tempForm displayOn: form at: 0 at y rule: Form blendAlphaUnscaled
  
  !

Item was changed:
  ----- Method: PNGReadWriter>>copyPixelsRGBA:at:by: (in category 'pixel copies') -----
  copyPixelsRGBA: y at: startX by: incX
  	"Handle interlaced RGBA color modes (colorType = 6)"
  
  	| i pixel tempForm tempBits |
  
  	tempForm := Form extent: width at 1 depth: 32.
  	tempBits := tempForm bits.
  	pixel := LargePositiveInteger new: 4.
  	bitsPerChannel = 8 ifTrue: [
  		i := (startX // incX << 2) + 1.
  		startX to: width-1 by: incX do: [ :x |
  			pixel at: 4 put: (thisScanline at: i+3);
  				at: 3 put: (thisScanline at: i);
  				at: 2 put: (thisScanline at: i+1);
  				at: 1 put: (thisScanline at: i+2).
  			tempBits at: x+1 put: pixel normalize.
  			i := i + 4.
  		]
  	] ifFalse: [
  		i := (startX // incX << 3) +1.
  		startX to: width-1 by: incX do: [ :x |
  			pixel at: 4 put: (thisScanline at: i+6);
  				at: 3 put: (thisScanline at: i);
  				at: 2 put: (thisScanline at: i+2);
  				at: 1 put: (thisScanline at: i+4).
  			tempBits at: x+1 put: pixel normalize.
  			i := i + 8.
  		].
  	].
+ 	tempForm displayOn: form at: 0 at y rule: Form paintAlpha.
- 	tempForm displayOn: form at: 0 at y rule: Form blendAlphaScaled.
  
  !