'From Squeak4.3 of 22 December 2011 [latest update: #11860] on 26 December 2011 at 4:02:31 pm'!

!Color class methodsFor: 'colormaps' stamp: 'spfa 12/26/2011 13:13'!
computeRGBColorConvertingMap: targetColor to: destDepth keepSubPixelAA: keepSubPix
	"Builds a colormap intended to convert from subpixelAA black values to targetColor values.
	keepSubPix
		ifTrue: [ Answer colors that also include subpixelAA ]
		ifFalse: [ 
			Take fullpixel luminance level. Apply it to targetColor.
			I.e. answer colors with NO subpixelAA ]"

	| mask map c bitsPerColor r g b f v |

	destDepth > 8
		ifTrue: [bitsPerColor := 5]  "retain maximum color resolution"
		ifFalse: [bitsPerColor := 4].
	"Usually a bit less is enough, but make it configurable"
	bitsPerColor := bitsPerColor min: Preferences aaFontsColormapDepth.
	mask := (1 bitShift: bitsPerColor) - 1.
	map := Bitmap new: (1 bitShift: (3 * bitsPerColor)).
	0 to: map size - 1 do: [:i |
		r := (i bitShift: 0 - (2 * bitsPerColor)) bitAnd: mask.
		g := (i bitShift: 0 - bitsPerColor) bitAnd: mask.
		b := (i bitShift: 0) bitAnd: mask.
		f := 1.0 - (r + g + b / 3.0 / mask).
		c := targetColor notNil
			ifTrue: [
				(keepSubPix and: [destDepth > 8]) ifTrue: [
						Color
							r: 1.0 - (r asFloat/mask) * targetColor red
							g: 1.0 - (g asFloat/mask) * targetColor green
							b: 1.0 - (b asFloat/mask) * targetColor blue
							alpha: f	* targetColor alpha "alpha will be ignored below, in #pixelValueForDepth: if destDepth ~= 32" ]
				ifFalse: [
					destDepth = 32
						ifTrue: [ targetColor * f alpha: f * targetColor alpha ]
						ifFalse: [ targetColor alphaMixed: f*1.5 with: Color white ]]]
			ifFalse: [ Color r: r g: g b: b range: mask].	"This is currently used only to keep some SubPixelAA on destDepth = 8, using a single pass of rule 25"
		v := destDepth = 32
			ifTrue: [ c pixelValueForDepth: destDepth]
			ifFalse: [
				f < 0.1
					ifTrue: [ 0 ]
					ifFalse: [ c pixelValueForDepth: destDepth ]].
		map at: i + 1 put: v ].
	^ map! !