Hi Maximilian,

This looks like a good addition. It is small and useful, and it aids
understanding.

I am not very knowledgeable about the BitBlt rules, so maybe someone
else can look at it also? To me, this looks like a good contribution
for trunk.

Dave


On Wed, Mar 20, 2019 at 12:51:46PM +0000, commits at source.squeak.org wrote:
> A new version of Graphics was added to project The Inbox:
> http://source.squeak.org/inbox/Graphics-ms.407.mcz
> 
> ==================== Summary ====================
> 
> Name: Graphics-ms.407
> Author: ms
> Time: 20 March 2019, 1:51:42.768596 pm
> UUID: 40a66bd7-815f-43f7-bbd0-31dc8da3a483
> Ancestors: Graphics-mt.406
> 
> Adds a preview morph for results of all BitBlt rules.
> 
> When first using BitBlt, it wasn't easy to understand the effects of the possible rules on pixel combinating for me.
> I implemented two example methods which preview the effects of rule 0 to 41 (these are all, I believe) on quadratic existing forms with colors and 1 bit alpha channel (previewAllBitBltRules uses ToolIcons flag/collection) plus Forms with more alpha values (previewAllBitBltRulesWithAlpha uses ToolIcons flag and a Color red + 0.4 alpha preview). They generate a combined morph for all rules applied on these forms (scaled, because icons are small) and opens it in your hand.
> Internally, this morph can be generated for any rule, forms and scale. Rules which throw exceptions are replaced with a fallback form.
> 
> =============== Diff against Graphics-mt.406 ===============
> 
> Item was added:
> + ----- Method: BitBlt class>>previewAllBitBltRules (in category 'examples') -----
> + previewAllBitBltRules
> + 
> + 	(self previewBitBltRules: (0 to: 41)
> + 		on: ToolIcons flag
> + 		and: ToolIcons collection
> + 		fallback: ToolIcons exception
> + 		scaledTo: 32) openInHand.!
> 
> Item was added:
> + ----- Method: BitBlt class>>previewAllBitBltRulesWithAlpha (in category 'examples') -----
> + previewAllBitBltRulesWithAlpha
> + 
> + 	(self previewBitBltRules: (0 to: 41)
> + 		on: ToolIcons flag
> + 		and: ((Color red alpha: 0.4) iconOrThumbnailOfSize: 12)
> + 		fallback: ToolIcons exception
> + 		scaledTo: 32) openInHand.!
> 
> Item was added:
> + ----- Method: BitBlt class>>previewBitBltRules:on:and:fallback:scaledTo: (in category 'examples') -----
> + previewBitBltRules: rules on: aForm1 and: aForm2 fallback: fallbackForm scaledTo: aNumberOrPoint
> + 	"Returns a combined morph of the result of each rule applied on aForm1 combined with 
> + 	aForm2 scaled to aNumberOrPoint. If the combination faild with a rule, fallbackForm is 
> + 	shown instead. The number of each rule is appended at the bottom of each result."
> + 
> + 	| resultMorph tileExtent |
> + 	tileExtent := aNumberOrPoint asPoint.
> + 	resultMorph := Morph new
> + 		color: Color transparent;
> + 		extent: (rules size * tileExtent x)@tileExtent y;
> + 		yourself.
> + 
> + 	rules withIndexDo: [ :rule :index | | form formMorph numberLabel |
> + 		form := aForm1 copy.
> + 		[aForm2 copy displayOn: form at: 0 at 0 rule: rule]
> + 			on: Exception 
> + 			do: [form := fallbackForm].
> + 		formMorph := (form scaledToSize: tileExtent) asMorph
> + 			position: (index*tileExtent x)@0;
> + 			yourself.
> + 		resultMorph addMorph: formMorph.
> + 	
> + 		numberLabel := rule asString asMorph
> + 	      	center: ((index+0.5)*tileExtent x)@tileExtent y;
> + 			yourself.
> + 		resultMorph addMorph: numberLabel].
> + 
> + 	^ resultMorph!
> 
>