_DONTBLEND - QB64Official/qb64 GitHub Wiki

The _DONTBLEND statement turns off 32 bit alpha blending for the current image or screen mode where _BLEND is default.

Syntax

_DONTBLEND [imageHandle&]

Parameter(s)

If imageHandle& is omitted, it is assumed to be the current _DESTination write page.

Description

If imageHandle& is not valid, an ERROR Codes error will occur.
_DONTBLEND is faster than the default _BLEND. You may want to disable it, unless you really need to use it in 32 bit.
32 bit screen surface backgrounds (black) have zero _ALPHA so that they are transparent when placed over other surfaces.
Use CLS to make a new surface background _ALPHA 255 or opaque.
Both _SOURCE and _DEST must have _BLEND enabled, or else colors will NOT blend.

Example(s)

Use _DONTBLEND when you want the 32 bit screen surface to be opaque so that it covers up other backgrounds. CLS works too.


SCREEN _NEWIMAGE(1280, 720, 32)
'CLS
_DONTBLEND '<<< comment out to see the difference

LINE (100, 100)-(500, 500), _RGB32(255, 255, 0), BF

b& = SaveBackground&

PRINT "This is just test junk"
PRINT
PRINT "Hit any key and the text should disappear, leaving us our pretty yellow box."
SLEEP
RestoreBackground b&

END

FUNCTION SaveBackground&
SaveBackground& = _COPYIMAGE(0)
END FUNCTION

SUB RestoreBackground (Image AS LONG)
_PUTIMAGE , Image, 0
END SUB

Turning off blending to create transparency.


SCREEN _NEWIMAGE(640, 480, 32)
alphaSprite& = _NEWIMAGE(64, 64, 32)

_DONTBLEND alphaSprite&   ' turn off alpha-blending

'Create a simple sprite with transparency
_DEST alphaSprite&
FOR y = 0 TO 63
  FOR x = 0 TO 63
    alpha = SQR((x - 32) ^ 2 + (y - 32) ^ 2) / 32
    IF alpha < 0 THEN alpha = 0
    alpha = (1 - alpha * alpha) 'parabolic curve
    PSET (x, y), _RGBA32(255, 255, 255, alpha * 255)
  NEXT
NEXT

'Make a simple background texture
_DEST 0
FOR y = 1 TO 479
  FOR x = 0 TO 639
    PSET (x, y), _RGB32(x AND 255, y AND 255, (x XOR y) AND 255)
  NEXT
NEXT

'Store background so we can show moveable objects on it
background& = _COPYIMAGE

'Treat my alpha values as transparency
_BLEND alphaSprite&

ph = 0
DO:  _LIMIT 60
  x = 320 - 250 * COS(ph) - (_WIDTH(alphaSprite&) \ 2)
  y = 240 - 150 * COS(ph * 1.3) - (_HEIGHT(alphaSprite&) \ 2)
  ph = ph + 0.03
  _PUTIMAGE , background&, 0
  _PUTIMAGE (x, y), alphaSprite&, 0
  _DISPLAY
LOOP UNTIL LEN(INKEY$)