_DONTBLEND
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The _DONTBLEND statement turns off 32 bit alpha blending for the current image or screen mode where _BLEND is default.
Syntax
- _DONTBLEND [imageHandle&]
Parameters
- If imageHandle& is omitted, it is assumed to be the current _DESTination write page.
Description
- If imageHandle& is not valid, an Invalid handle 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.
Examples
Example 1: 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 |
Example 2: 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(0) '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$) |
Explanation: To make the alpha image, turn alpha blending off. Otherwise PSET blends the pixel to instead of making the sprite transparent.
See also