Patrick Rein uploaded a new version of Graphics to project The Trunk: http://source.squeak.org/trunk/Graphics-pre.404.mcz
==================== Summary ====================
Name: Graphics-pre.404 Author: pre Time: 15 October 2018, 9:57:15.384742 am UUID: a816199d-b2b6-7247-a8f8-898c605829df Ancestors: Graphics-pre.403
Removes odd behavior of colorFromPixelValue:depth: which returns transparent instead of 32bit rgb black
=============== Diff against Graphics-pre.403 ===============
Item was changed: ----- Method: Color class>>colorFromPixelValue:depth: (in category 'instance creation') ----- colorFromPixelValue: p depth: d "Convert a pixel value for the given display depth into a color." "Details: For depths of 8 or less, the pixel value is simply looked up in a table. For greater depths, the color components are extracted and converted into a color."
| r g b alpha | d = 8 ifTrue: [^ IndexedColors at: (p bitAnd: 16rFF) + 1]. d = 4 ifTrue: [^ IndexedColors at: (p bitAnd: 16r0F) + 1]. d = 2 ifTrue: [^ IndexedColors at: (p bitAnd: 16r03) + 1]. d = 1 ifTrue: [^ IndexedColors at: (p bitAnd: 16r01) + 1].
(d = 16) | (d = 15) ifTrue: [ "five bits per component" r := (p bitShift: -10) bitAnd: 16r1F. g := (p bitShift: -5) bitAnd: 16r1F. b := p bitAnd: 16r1F. (r = 0 and: [g = 0]) ifTrue: [ b = 0 ifTrue: [^Color transparent]. b = 1 ifTrue: [^Color black]]. ^ Color r: r g: g b: b range: 31].
d = 32 ifTrue: [ "eight bits per component; 8 bits of alpha" r := (p bitShift: -16) bitAnd: 16rFF. g := (p bitShift: -8) bitAnd: 16rFF. b := p bitAnd: 16rFF. alpha := p bitShift: -24. alpha = 0 ifTrue: [^Color transparent]. - (r = 0 and: [g = 0 and: [b = 0]]) ifTrue: [^Color transparent]. alpha < 255 ifTrue: [^ (Color r: r g: g b: b range: 255) alpha: (alpha asFloat / 255.0)] ifFalse: [^ (Color r: r g: g b: b range: 255)]].
d = 12 ifTrue: [ "four bits per component" r := (p bitShift: -8) bitAnd: 16rF. g := (p bitShift: -4) bitAnd: 16rF. b := p bitAnd: 16rF. ^ Color r: r g: g b: b range: 15].
d = 9 ifTrue: [ "three bits per component" r := (p bitShift: -6) bitAnd: 16r7. g := (p bitShift: -3) bitAnd: 16r7. b := p bitAnd: 16r7. ^ Color r: r g: g b: b range: 7].
self error: 'unknown pixel depth: ', d printString !
On 2018-10-15, at 1:57 AM, commits@source.squeak.org wrote:
Patrick Rein uploaded a new version of Graphics to project The Trunk: http://source.squeak.org/trunk/Graphics-pre.404.mcz
==================== Summary ====================
Name: Graphics-pre.404 Author: pre Time: 15 October 2018, 9:57:15.384742 am UUID: a816199d-b2b6-7247-a8f8-898c605829df Ancestors: Graphics-pre.403
Removes odd behavior of colorFromPixelValue:depth: which returns transparent instead of 32bit rgb black
Umm, as best I remember we expect and require 32bit 0.0.0.0 to be transparent. It is an artefact from way back and has caused much confusion; but a lot of code is based on it.
If you've found a way to avoid it and not break all that code - or better yet, I'm misremembering! - then good.
tim -- tim Rowledge; tim@rowledge.org; http://www.rowledge.org/tim Advanced design: Upper management doesn't understand it.
On Mon, Oct 15, 2018 at 1:17 PM tim Rowledge tim@rowledge.org wrote:
On 2018-10-15, at 1:57 AM, commits@source.squeak.org wrote:
Patrick Rein uploaded a new version of Graphics to project The Trunk: http://source.squeak.org/trunk/Graphics-pre.404.mcz
==================== Summary ====================
Name: Graphics-pre.404 Author: pre Time: 15 October 2018, 9:57:15.384742 am UUID: a816199d-b2b6-7247-a8f8-898c605829df Ancestors: Graphics-pre.403
Removes odd behavior of colorFromPixelValue:depth: which returns
transparent instead of 32bit rgb black
Umm, as best I remember we expect and require 32bit 0.0.0.0 to be transparent. It is an artefact from way back and has caused much confusion; but a lot of code is based on it.
0-0-0-0 is transparent because alpha is 0, that is not the issue. But 255-0-0-0 also used to be treated as transparent because that's what you get when converting from a 16 bit form, in which 0-0-0 is treated as transparent by certain bitblt rules, whereas 0-0-1 is black. Cf. fixAlpha.
(Color black pixelValueForDepth: 16) hex => 16r0001 (Color black pixelValueForDepth: 32) hex => 16rFF000001
(Color transparent pixelValueForDepth: 16) hex => 16r0000 (Color transparent pixelValueForDepth: 32) hex => 16r00000000
If you've found a way to avoid it and not break all that code - or better
yet, I'm misremembering! - then good.
We're not doing a lot of 16/32 bpp conversions nowadays so I expect we won't run into too many issues. Someone should check the bitblt rules to see which ones treat the x-0-0-0 value specially.
- Bert -
Hi all,
the change is reverted now but I would like to document our findings and our insights for future changes.
From Berts mail I gathered that the 255-0-0-0 to be transparent is required for 16bit -> 32bit conversion to work. As this has been around for quite some time some code relies on it. At the same time this regularly leads to problems when working with images loaded from external sources. For example, loading a PNG and using collectColor: to recolor it does not work if the PNG includes pure rgb black pixels. For this to work we would have to map pure black to Squeak Form black on loading and reconvert it on storing. This would however destroy information as we can not distinguish between 0-0-1 and 0-0-0 anymore. The other way to go would be to change the 16bit -> 32bit conversion to set alpha explicitly, but I do not know whether that is actually possible efficiently.
Are there other aspects which I am missing? Is it likely for external packages to heavily rely on this functionality?
Bests Patrick
On 2018-10-15, at 1:57 AM, commits@source.squeak.org wrote:
Patrick Rein uploaded a new version of Graphics to project The Trunk: http://source.squeak.org/trunk/Graphics-pre.404.mcz
==================== Summary ====================
Name: Graphics-pre.404 Author: pre Time: 15 October 2018, 9:57:15.384742 am UUID: a816199d-b2b6-7247-a8f8-898c605829df Ancestors: Graphics-pre.403
Removes odd behavior of colorFromPixelValue:depth: which returns transparent instead of 32bit rgb black
Umm, as best I remember we expect and require 32bit 0.0.0.0 to be transparent. It is an artefact from way back and has caused much confusion; but a lot of code is based on it.
If you've found a way to avoid it and not break all that code - or better yet, I'm misremembering! - then good.
tim
tim Rowledge; tim@rowledge.org; http://www.rowledge.org/tim Advanced design: Upper management doesn't understand it.
squeak-dev@lists.squeakfoundation.org
-
Bert Freudenberg -
commits＠source.squeak.org -
patrick.rein＠hpi.uni-potsdam.de -
tim Rowledge