ASM Community

This is my code, how is yours? :grin:

rol edx,16

ror eax,8

and eax,0ffff00ffh

add dx,ax

shr edx,24

add ax,dx

and eax,0ffffh

xor edx,edx

 push ebx

mov ebx,3

div ebx

 pop ebx

This code assumes the color is in 00RRGGBB format (or 00BBGGRR, that doesn't matter). I have to preserve ebx,ecx,esi, and edi because of the loop this code is in.

Maybe this is better?

	mov edx,eax

	shr eax,16	; assumes top byte is zero



	add dl,dh

	adc ah,0



	add al,dl

	adc ah,0



	mul DIV3MUL

	; Answer in EDX

I'm sure you know that this is not truely the brightness due to human
eyes seeing primary colors in different bais (ie green is very strong).

Hmm... at least I have some interesting replies. Thanks all!

I'll tell a bit more about the program this was for, if you're interested. I'm currently working on a very nice transparent (UpdateLayeredWindow, so XP/2K only) user interface thingie, that uses a png with alpha channel that is 3 by 3 "tiles" (32x32 pixels each) large to paint an entire image. It looks nice with the partial transparency and all, but I wanted to be able to print opaque text to it. That's how it started...

This is how I currently do it:

1. Paint black-on-white text on tmpDC
2. Process the painted block pixel by pixel, and if the inverse (not'ed) brightness of a pixel is larger than the window's transparency at that point, the transparency is replaced with the not'ed brightness.
3. BitBlt the window part that the text will be painted on to tmpDC
4. Draw the text with transparent (SetBkMode,tmpDC,TRANSPARENT) background to tmpDC
5. Copy the pixel block from tmpDC back to the main window DC, without overwriting the alpha values.

This works ok if your window isn't too transparent, otherwise ClearType screws up and makes the edges look really ugly.

bitRAKE, I know this isn't the real brightness, but it's good enough for my purpose since most of the pixels are gray anyway (except for the ClearType ones of course).

It already moves quite smoothly (I have show window contents while dragging enabled). In fact I haven't been able to make it flicker, but that's pretty logical when you realize the UpdateLayeredWindow and the painting is only done once in the program and windows takes care of the rest :)
Perhaps if I have multiple windows moving on a timer... will try it out one time.

Also, another question: I've just dusted off your Fast Alpha Blend algo, and I'm wondering what it does with the alpha values of the destination? For my purpose it'd be ideal if it added the two alpha values (clipping at 255 of course), but I don't think it's likely it already does that.

I don't know MMX (yet)...

Nexo - thanks but that code is even farther away from what I want to do than bitRAKE's is. What I need is:

src = argb
dst = argb

where a is the one-byte alpha value for that pixel.

dst(a) = src(a)+dst(a)
dst(r) = src(r) * src(a) + dst(r) * (255 - src(a))

(Green and blue in the same way as red)

bitRAKE's does exactly what I want, except it does something strange with the destination's alpha value.

:stupid: ? May be change comments?

; mm0=0

; mm1=b(a0,r0,g0,b0,A0,R0,G0,B0) - a

; mm2=b(a1,r1,g1,b1,A1,R1,G1,B1) - b

; mm3=w(a0,a0,A0,A0) - c[0..FF]

	movq mm6,mm2

	movq mm5,mm1

	punpcklbw mm2,mm0	;mm2=w(r1,b1,R1,B1)

	punpckhbw mm6,mm0	;mm6=w(a1,g1,A1,G1)

	punpcklbw mm1,mm0	;mm1=w(r0,b0,R0,B0)

	punpckhbw mm5,mm0	;mm5=w(a0,g0,A0,G0)

	psubsw mm2,mm1

	psubsw mm6,mm5	;mm6:mm2=b-a

	psllw mm1,8

	psllw mm5,8		;mm5:mm1'=a

	pmullw mm2,mm3

	pmullw mm6,mm3	;mm6:mm2'=c*(b-a)

	paddw mm1,mm2

	paddw mm5,mm6	;mm5:mm1'=a+c*(b-a)

	psrlw mm1,8

	psrlw mm5,8	;mm5:mm1=a+c*(b-a)

	packuswb mm5,mm1	;mm5=b(a2,r2,g2,b2,A2,R2,G2,B2)

; mm5=result

bitRAKE, it is per-pixel alpha?

bitRAKE, I was think, you add a couple instructions ;)

; mm1=b(a0,r0,g0,b0,A0,R0,G0,B0) - a

	pshufw mm3,mm1,11110101b

	psrlw mm3,8

; mm3=w(a0,a0,A0,A0) - c[0..FF]

(a0,r0,g0,b0) - one source pixel; (A0,R0,G0,B0) - two source pixel; a0,A0 - alpha.
I think this per-pixel alpha blend :) Is not it?

Best regards, Nexo.