Alpha Male

BlitzMax Forums/BlitzMax Beginners Area/Alpha Male

dw817

(Posted 2016) [#1]

If any of you have experimented with trying to read ALPHA off of a screen, you may have run into some difficulties.

Here is my attempt at it. Notice the first text that appears, and compare that w the last. You will definitely see a difference.

My question is, what code can be changed in this to make this work properly so the first text that appears also appears perfectly in the last ?

' Attempt to read and write ALPHA in plotted Truetype Font
Strict

Local typ=1
' typ = 0 do not use alpha buffer
' typ = 1 use alpha buffer

SetGraphicsDriver GLMax2DDriver(),0
Graphics 800,600,0,0,graphics_alphabuffer*typ
SetBlend alphablend

Local fnt:timagefont=LoadImageFont("c:\windows\fonts\tahoma.ttf",16)
Local img:TImage=CreateImage(512,90)
Local pic:TPixmap=CreatePixmap(256,24,pf_rgba8888)

Local i,j,r,g,b,a,n

SetImageFont fnt
SetClsColor 50,100,150
Cls
SetColor 1,1,1
DrawText "Amazing Grace.",2,2
SetColor 255,255,255
DrawText "Amazing Grace.",0,0
Flip 0
WaitKey
SetClsColor 0,0,0
Cls
SetColor 1,1,1
DrawText "Amazing Grace.",2,2
SetColor 255,255,255
DrawText "Amazing Grace.",0,0
pic=GrabPixmap(0,0,256,24)

For i=0 Until 23
  For j=0 Until 127
    n=j*4+i*256*4
    r=pic.pixels[n]
    g=pic.pixels[n+1]
    b=pic.pixels[n+2]
    a=pic.pixels[n+3]
    n:+128*4
    pic.pixels[n]=r
    pic.pixels[n+1]=g
    pic.pixels[n+2]=b
    pic.pixels[n+3]=a
  Next
'  SetMaskColor 0,0,0 ' Doesn't seem to do anything here ?
  img=LoadImage(pic,maskedimage)
  img.SetPixmap(0,MaskPixmap(LockImage(img),0,0,0)) ' this works but I don't think it gives proper alpha
  DrawImage img,0,0
  Flip 0
Next
Flip 0
WaitKey

SetClsColor 50,100,150
Cls
DrawImage img,0,0

Flip 0
WaitKey

Midimaster

(Posted 2016) [#2]

I tried the same on monkey target. A better idea is to guess the (former) alpha value from difference between set color and resulting color. f.e. If you draw a white (255,255,255) font on a black screen then the resulting grey values are the alpha informations for your image. The three colors still remain 255.

Derron

(Posted 2016) [#3]

I software render the glyphs on an image/pixmap - so I could preserve alpha.

Just remember: Each TImageFont has an "glyph-image" stored for each character.

If you need some hints for implementation:
https://github.com/GWRon/Dig/blob/master/base.gfx.bitmapfont.bmx

Of course this does not add "alpha-channel-backbuffers". For this you better use Render2Texture (there is code around in the forums, as you indirectly asked for this some weeks ago)...

bye
Ron

dw817

(Posted 2016) [#4]

I solved this without having to go through all that. My code of 6-lines versus the 880 you presented nor need of Render2Texture. :) Appreciate the help tho Midimaster and Ron.