Hi Eric,

> Note that in this version, the tests are currently failing because -- apparently -- drawing Color black to a FormCanvas actually results in a slightly different color being put at the corresponding pixels of the Form. Therefore the expected values (Color black) are something else.
>   
> I suspect this is an issue with Form/FormCanvas?

Here is a small bit of additional information on this issue (I don't understand the issue myself, but I have already searched for this on the list recently for another student's question, so maybe this is helpful for anyone): See also GraphicsTests-pre.49.
It looks as if 32-bit forms in Squeak basically do not support black pixels for what ever reason. You could check whether issue persists when you choose a lower bit depth.

Sorry, that is the only dim light I can shed on this issue ...

Best,
Christoph

---
Sent from Squeak Inbox Talk

On 2022-05-04T11:08:41+00:00, commits at source.squeak.org wrote:

> Marcel Taeumel uploaded a new version of GraphicsTests to project The Trunk:
> http://source.squeak.org/trunk/GraphicsTests-EG.58.mcz
> 
> ==================== Summary ====================
> 
> Name: GraphicsTests-EG.58
> Author: EG
> Time: 21 December 2021, 7:06:22.53722 pm
> UUID: 32f0cb4a-a10f-4263-85da-6d934e567b0d
> Ancestors: GraphicsTests-mt.57
> 
> Adding actual tests for GIF reading and writing (and reading back in).
>   
> Note that in this version, the tests are currently failing because -- apparently -- drawing Color black to a FormCanvas actually results in a slightly different color being put at the corresponding pixels of the Form. Therefore the expected values (Color black) are something else.
>   
> I suspect this is an issue with Form/FormCanvas?
> 
> =============== Diff against GraphicsTests-mt.57 ===============
> 
> Item was added:
> + TestCase subclass: #GIFReadWriterTest
> +     instanceVariableNames: ''
> +     classVariableNames: ''
> +     poolDictionaries: ''
> +     category: 'GraphicsTests-Files'!
> 
> Item was added:
> + ----- Method: GIFReadWriterTest>>animatedColorFrames (in category 'tests') -----
> + animatedColorFrames
> +     "Responds with a collection of AnimatedImageFrames
> +     each containing equal-sized rectangles of green, red, 
> +     yellow. and black. When animated, these rectangles move
> +     into each other's positions, then back"
> +     | frames topLeft topRight bottomLeft bottomRight revFrames |
> +     frames := OrderedCollection new.
> +     topLeft := (0 at 0 extent: 200 at 200).
> +     topRight := (200 at 0 extent: 400 at 200).
> +     bottomLeft := (0 at 200 extent: 200 at 400).
> +     bottomRight := (200 at 200 extent: 400 at 400).
> +     
> +     0 to: 200 by: 20 do: [ :num |
> +         | newTopLeft newTopRight newBottomLeft newBottomRight canvas |
> +         newTopLeft := topLeft translateBy: (num at 0).
> +         newTopRight := topRight translateBy: (0 at num).
> +         newBottomLeft := (bottomLeft origin - (0 at num)) corner: (bottomLeft extent - (0 at num)).
> +         newBottomRight := (bottomRight origin - (num at 0)) extent: (bottomLeft extent - (0 at 0)).
> +         canvas := FormCanvas extent: 400 at 400 depth: 32.
> +         canvas
> +             fillRectangle: newTopLeft color: Color green;
> +             fillRectangle: newTopRight color: Color red;
> +             fillRectangle: newBottomLeft color: Color yellow;
> +             fillRectangle: newBottomRight color: Color black.
> +         frames add: (AnimatedImageFrame new
> +             form: canvas form;
> +             disposal: #restoreBackground;
> +             delay: 60) ].
> + 
> +     revFrames := frames reversed.
> +     revFrames do: [ :f | frames add: f ].
> +     ^ frames!
> 
> Item was added:
> + ----- Method: GIFReadWriterTest>>testAnimatedColorsOutIn (in category 'tests') -----
> + testAnimatedColorsOutIn
> +     "Ensure that the colored rectangles in the created
> +     animated gif are correct at different frames"
> +     | frames outBytes writer reader inBytes activeFrame |
> +     frames := self animatedColorFrames.
> +     
> +     "Write out the GIF bytes to the byte stream"
> +     outBytes := WriteStream on: (ByteArray new).
> +     writer := GIFReadWriter on: outBytes.
> +     frames do: [ :f | writer nextPutFrame: f ].
> +     writer close.
> +     
> +     "Read the GIF byte stream back into a GIF"
> +     inBytes := ReadStream on: (outBytes contents).
> +     reader := GIFReadWriter on: inBytes.
> +     reader
> +         readHeader;
> +         readBody.
> +     
> +     self assert: reader isAnimated equals: true.
> +     activeFrame := reader frames at: 1.
> +     self assert: (activeFrame form colorAt: 100 at 100) equals: Color green.
> +     self assert: (activeFrame form colorAt: 300 at 100) equals: Color red.
> +     self assert: (activeFrame form colorAt: 100 at 300) equals: Color yellow.
> +     self assert: (activeFrame form colorAt: 300 at 300) equals: Color black.
> +     activeFrame := reader frames at: 11.
> +     self assert: (activeFrame form colorAt: 100 at 100) equals: Color yellow.
> +     self assert: (activeFrame form colorAt: 300 at 100) equals: Color green.
> +     self assert: (activeFrame form colorAt: 100 at 300) equals: Color black.
> +     self assert: (activeFrame form colorAt: 300 at 300) equals: Color red.
> +     !
> 
> Item was added:
> + ----- Method: GIFReadWriterTest>>testColorsFileOutIn (in category 'tests') -----
> + testColorsFileOutIn
> +     "Ensure that the colors that are written match up
> +     to the colors that are read in again"
> +     | canvas form outBytes inBytes writer reader |
> +     canvas := FormCanvas extent: 400 at 400.
> +     canvas
> +         fillRectangle: (0 at 0 extent: 200 at 200) color: Color green;
> +         fillRectangle: (200 at 0 extent: 400 at 200) color: Color red;
> +         fillRectangle: (0 at 200 extent: 200 at 400) color: Color yellow;
> +         fillRectangle: (200 at 200 extent: 400 at 400) color: Color black.
> +     form := canvas form.
> +     outBytes := FileStream fileNamed: 'testColorsFileOutIn.gif'.
> +     writer := GIFReadWriter on: outBytes.
> +     writer
> +         nextPutImage: form;
> +         close.
> +     inBytes := 'testColorsFileOutIn.gif' asDirectoryEntry readStream binary.
> +     reader := GIFReadWriter on: inBytes.
> +     reader
> +         readHeader;
> +         readBody.
> +     inBytes close.
> +     'testColorsFileOutIn.gif' asDirectoryEntry delete.
> +     self assert: reader isAnimated equals: false.
> +     self assert: (reader form colorAt: 50 at 50) equals: Color green.
> +     self assert: (reader form colorAt: 250 at 50) equals: Color red.
> +     self assert: (reader form colorAt: 50 at 250) equals: Color yellow.
> +     self assert: (reader form colorAt: 250 at 250) equals: Color black.!
> 
> Item was added:
> + ----- Method: GIFReadWriterTest>>testColorsOutIn (in category 'tests') -----
> + testColorsOutIn
> +     "Ensure that the colors that are written match up
> +     to the colors that are read in again"
> +     | canvas form outBytes inBytes writer reader |
> +     canvas := FormCanvas extent: 400 at 400.
> +     canvas
> +         fillRectangle: (0 at 0 extent: 200 at 200) color: Color green;
> +         fillRectangle: (200 at 0 extent: 400 at 200) color: Color red;
> +         fillRectangle: (0 at 200 extent: 200 at 400) color: Color yellow;
> +         fillRectangle: (200 at 200 extent: 400 at 400) color: Color black.
> +     form := canvas form.
> +     outBytes := WriteStream on: (ByteArray new).
> +     writer := GIFReadWriter on: outBytes.
> +     writer
> +         nextPutImage: form;
> +         close.
> +     outBytes := outBytes contents.
> +     inBytes := ReadStream on: outBytes.
> +     reader := GIFReadWriter on: inBytes.
> +     reader
> +         readHeader;
> +         readBody.
> +     self assert: reader isAnimated equals: false.
> +     self assert: (reader form colorAt: 50 at 50) equals: Color green.
> +     self assert: (reader form colorAt: 250 at 50) equals: Color red.
> +     self assert: (reader form colorAt: 50 at 250) equals: Color yellow.
> +     self assert: (reader form colorAt: 250 at 250) equals: Color black.!
> 
> 
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