0005605: Squeak oxymorons: MatrixTransform2x3 identity does not behave as an identiy transformation.

Viewing Issue Simple Details [ Jump to Notes ]

[ View Advanced ] [ Issue History ] [ Print ]

Category

Severity

Reproducibility

Date Submitted

Last Update

0005605

[Squeak] Graphics

feature

always

12-05-06 06:44

03-07-07 06:52

Reporter

wiz

View Status

public

Assigned To

andreas

Priority

normal

Resolution

open

Status

assigned

Product Version

3.9

Summary

0005605: Squeak oxymorons: MatrixTransform2x3 identity does not behave as an identiy transformation.

Description

For this one in a fresh Sq 7067
evaluate in a workspace:

results :=
{ IdentityTransform identity
. MatrixTransform2x3 identity
. MorphicTransform identity } collect: [ :each |
( -2.0 to: 2.0 by: 0.25 ) collect: [ :eachOne |
(each globalPointToLocal: (each localPointToGlobal: eachOne asPoint )) ]] .

results explore .

And compare the results.

Additional Information

My results were:

root: {see expanded lists}
    1: {IdentityTransform}
        1: -2.0@-2.0
        2: -1.75@-1.75
        3: -1.5@-1.5
        4: -1.25@-1.25
        5: -1.0@-1.0
        6: -0.75@-0.75
        7: -0.5@-0.5
        8: -0.25@-0.25
        9: 0.0@0.0
        10: 0.25@0.25
        11: 0.5@0.5
        12: 0.75@0.75
        13: 1.0@1.0
        14: 1.25@1.25
        15: 1.5@1.5
        16: 1.75@1.75
        17: 2.0@2.0
    2: {MatrixTransform2x3}
        1: 0@0
        2: 0@0
        3: 0@0
        4: 0@0
        5: 0@0
        6: 0@0
        7: 0@0
        8: 0@0
        9: 0@0
        10: 0@0
        11: 1@1
        12: 1@1
        13: 1@1
        14: 1@1
        15: 2@2
        16: 2@2
        17: 2@2
    3: {MorphicTransform}
        1: -2.0@-2.0
        2: -1.75@-1.75
        3: -1.5@-1.5
        4: -1.25@-1.25
        5: -1.0@-1.0
        6: -0.75@-0.75
        7: -0.5@-0.5
        8: -0.25@-0.25
        9: 0.0@0.0
        10: 0.25@0.25
        11: 0.5@0.5
        12: 0.75@0.75
        13: 1.0@1.0
        14: 1.25@1.25
        15: 1.5@1.5
        16: 1.75@1.75
        17: 2.0@2.0

Now to be fair to MatrixTransform2x3 has two methods for transforming points

#transformPoint:
#invertPoint
which do the transformation w/o "rounding" . Using them in place of
#globalPointToLocal: and #localPointToGlobal in a separate test gives the expected results.

These messages have few senders. And they are not part of the DisplayTransform protocol.
It would make more sense to me it the senses were reversed. With the protocol messages behaving like IdentityMorph and the two messages unique to MatrixTransform2x3 behaving in the unusual way. (i.e. rounding)

I was also surprised to find that in addition to rounding, negative numbers are transformed to 0? What is that in aid of?

MatrixTransform2x3 seem to me to be an oddball. And there seem to be no flags out there to say why and to document how to properly use its behavior.

Attached Files

Relationships

SYSTEM WARNING: Creating default object from empty value

related to	0006303	new	Matrix2x3Plugin does not consider negative numbers when rounding.
child of	0006511	new	Mother of all Morphic Graphical off-by-one/fencepost -error reports.
child of	0005560	new	MatrixTransformationMorph needs examining and fixing.

Notes
(0008775 - 276 - 324 - 324 - 324 - 324 - 324) wiz 12-30-06 02:23 edited on: 12-30-06 02:24	On more reflection: The problem seems to be related to doing rounding using n + 1 truncate. Which works when n is positve but will be off by one or even two when n = aNegativeInteger + positiveEpsilon . And that seems to be the case here. So this is really a bug.

Issue History
Date Modified	Username	Field	Change
12-05-06 06:44	wiz	New Issue
12-05-06 06:44	wiz	Status	new => assigned
12-05-06 06:44	wiz	Assigned To	=> andreas
12-30-06 02:23	wiz	Note Added: 0008775
12-30-06 02:24	wiz	Note Edited: 0008775
03-07-07 06:52	wiz	Relationship added	related to 0006303
05-25-07 02:47	wiz	Relationship added	related to 0006511
05-25-07 02:59	wiz	Relationship replaced	child of 0006511
07-05-07 00:45	wiz	Relationship added	child of 0005560

Mantis 1.0.8[^]

55 total queries executed.
38 unique queries executed.