Alpha Sprites

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SoCoder -> Snippet Home -> Graphical Effects

Andy_A	Created : 23 February 2008 System : Windows Language : Blitz Alpha Sprites Realtime alpha blended sprites
Here's a simple to use alpha-sprite routine. Routine originally posted by 'ford escort' https://www.blitzbasic.com/codearcs/codearcs.php?code=913 I've made a few optimizations to decrease time it takes to read the sprite image into a 'bank' and to decrease the time it takes to write the 'alpha-blended' sprite. Have also included a simple demo to see how it should work. Should be able to handle multiple alpha-sprites. Keep the images down to 64x64 pixels maximum for best results. Andy ;transparent sprites in b+ by ford escort ;original source here: ;https://www.blitzbasic.com/codearcs/codearcs.php?code=913 ; ; ;Inner-loop optimizations and simple demo by Andy_A AppTitle "transparent sprites" ;------this must be included before the functions call Dim lookup#(255), img%(255), bkd%(255) populate() ;<- fills look-up table Global sw=640,sh=480 Global hSprite%, bknd% Graphics sw,sh,32,2 SetBuffer BackBuffer() SeedRnd MilliSecs() ;create simple graphics setUpGraphics() bankPointer% = bufferize(hSprite%,1,0,0,0) fntArial20% = LoadFont("Arial",20,True,False,False) SetFont fntArial20% Color 32,190,255 inc% = 5 blinkRate% = 64 ;<-- blink rate in milliseconds maskFlag% = 1 ;<-- change to 0 for no masking While MouseHit(1)=0 Cls DrawBlock bknd,0,0 x = MouseX() y = MouseY() If st < MilliSecs() Then st = MilliSecs() + blinkRate% pct% = pct% + inc% If pct% > 95 Then inc% = -5 If pct% < 5 Then inc% = 5 End If Text (320,445,"'Click' to exit.",True,False) alphasprite(bankPointer,x,y,pct%,maskFlag%) Flip Wend FreeBank bankPointer% FreeImage bknd% End ;------------------------------------------------------ Function bufferize%(image%, flag%, rm%, gm%, bm%) ; this function converts a picture to an rgb coded memorybank ; set flag=1 to free the memory of the original image after 'bufferize-ing' ; rm,gm,bm rgb of the color mask (not drawn) Local w%, h%, bank%, rgbVal%, offset%, x%, y%, r%, g%, b% w=ImageWidth(image) ; get image width h=ImageHeight(image) ; get image height bank=CreateBank((wh3)+7) ; allot first 4 bytes to store the width and height ; of the picture+3 For the mask LockBuffer ImageBuffer(image) ; lock the buffer to speedup things PokeShort(bank,0,w) ; store the image width PokeShort(bank,2,h) ; store the image height PokeByte(bank,4,rm) ; store the red mask value PokeByte(bank,5,gm) ; store the green mask value PokeByte(bank,6,bm) ; store the blue mask value rgbVal% = CreateBank(4) ; 4 byte bank stores value of ReadPixelFast() offset=7 For y=0 To h-1 For x=0 To w-1 ; read current pixel into rgbVal% bank PokeInt(rgbVal%, 0,ReadPixelFast(x,y, ImageBuffer(image))) ; Store directly into bank (no SHIFTing! No ANDing! Very Fast!) PokeByte bank,offset,PeekByte(rgbVal%,2) ;store current pixel red value offset=offset+1 PokeByte bank,offset,PeekByte(rgbVal%,1) ;store current pixel grn value offset=offset+1 PokeByte bank,offset,PeekByte(rgbVal%,0) ;store current pixel blu value offset=offset+1 Next Next UnlockBuffer ImageBuffer(image) If flag=1 FreeImage image End If FreeBank rgbVal% Return bank End Function ;usage: ; ; ;=================== alphasprite(bank, xx, yy, percent, flag) ======================= ; bank : the handle of the bank containing the sprite (made with bufferize function) ; xx,yy: onscreen coordinate where the sprite will be drawn ; percent: transparency percentage ; flag : if set to 1 then mask color will not be drawn (same as maskimage) ; ;this draws the image previously saved in memory to x,y coords specified ;percent is the amount of opacity (0% = transparent, 100% = opaque) ;If flag=1 then masking color of memory saved image is NOT blended or drawn Function alphasprite(bank%, xx%, yy%, percent%, flag%) Local buffer%, gtw%, gth%, w%, h%, rm%, gm%, bm%, pixRGB% Local i%, offset%, y%, x%, r1%, g1%, b1%, r2%, g2%, b2% ;make sure percent is within valid range of 0 <= percent <= 100 If percent < 0 Or percent > 100 Then percent = percent Mod 101 buffer=GraphicsBuffer() gtw=GraphicsWidth() gth=GraphicsHeight() w=PeekShort(bank,0) h=PeekShort(bank,2) rm=PeekByte(bank,4) gm=PeekByte(bank,5) bm=PeekByte(bank,6) pixRGB% = CreateBank(4) ; 4 byte bank stores value of ReadPixelFast() ; The bigger the image, the more cycles this saves ; as long as the image is 8x16 (128 pixels) or larger For i = 0 To 255 img%(i) = Floor( lookup(i) * percent ) bkd%(i) = Floor( lookup(i) * (100-percent) ) Next offset=7 LockBuffer buffer For y=0 To h-1 For x=0 To w-1 r2=PeekByte(bank,offset) ; r offset=offset+1 ; g g2=PeekByte(bank,offset) ; b offset=offset+1 ; values b2=PeekByte(bank,offset) ; of the offset=offset+1 ; bufferized image If xx+x<=gtw And yy+y<=gth ; the coordinates are in the drawing buffer If flag=0 Or (flag=1 And r2<>rm Or g2<>gm Or b2<>bm); the flag =0 or the colors are not the masked colors ; read the current pixel into pixRGB% bank PokeInt(pixRGB%, 0,ReadPixelFast(xx+x, yy+y, buffer)) ; store new rgb values into pixRGB% bank PokeByte(pixRGB%, 2, img(r2)+bkd(PeekByte(pixRGB%,2))) ;r1)) PokeByte(pixRGB%, 1, img(g2)+bkd(PeekByte(pixRGB%,1))) ;g1)) PokeByte(pixRGB%, 0, img(b2)+bkd(PeekByte(pixRGB%,0))) ;b1)) ;draw the alpha-blended pixel WritePixelFast xx+x, yy+y, PeekInt(pixRGB%,0), buffer End If End If Next Next UnlockBuffer buffer FreeBank pixRGB% End Function ;Create simple sprite and place random rect's on screen to see alpha effect Function setUpGraphics%() Local fntArial36B%, textWide%, textHigh% Local i%, j%, k%, r%, g%, b% Local msg$ Cls fntArial36B = LoadFont("Arial", 36, True,False,False) SetFont fntArial36B% msg$ = "Alpha-Sprite!" ;<- place your own message here txtWide% = StringWidth(msg$) txtHigh% = StringHeight(msg$) hSprite% = CreateImage(txtWide%, txtHigh%) Color 255, 255, 255 ;set color of text Text 100, 100, msg$ GrabImage(hSprite%, 100, 100) Cls For i% = 1 To 400 r% = Rand(0,192) g% = Rand(0,176) b% = Rand(0,255) Color r%, g%, b% j% = Rand(-50,540) k% = Rand(-50,380) Rect j%, k%, Rand(60,150), Rand(60,150),True Color 255-r%, 255-g%, 255-b% j% = Rand(-50,540) k% = Rand(-50,380) Oval j%, k%, Rand(60,150), Rand(60,150),True Next Color 0,0,0 Oval 240,435,160,40 SetBuffer BackBuffer() ;create image buffer the size of current window bknd% = CreateImage(GraphicsWidth(), GraphicsHeight()) ;grab what's on the screen and store in image buffer GrabImage(bknd%, 0, 0) FreeFont fntArial36B% End Function ; fill the look-up table with float values Function populate() For a=0 To 255 lookup#(a)=Float(a)/100.0 Next End Function --v

Comments
Sunday, 24 February 2008, 06:41
Jayenkai	Nicely done. Plenty of work to get it done, though. Such a shame that Blitz doesn't natively do all that in the first place. Either way, a neat effect if you need a certain limited amount of transparent stuff on screen. (like flickering flames, or things like that.) In fact, it'd probably be even more useful for overlaying sprites atop one another whilst loading. eg, you could have a preset "Shadow" transparency element, then load a single bitmap and generate an entire of wall/shadow tilemap from it. v-- Click to enlarge for illustrated explaination! --v Essentially, if I'd have used this method whilst making my Oh Mummy remake, I could've generated an infinite number of randomly colored base tiles, and then generated the tilemaps ingame quite easily, per level. This could've lead to hundreds of color-combo levels, rather than just having the 6 colored tilemaps I'd pre-generated. Either way, could come in handy!
Sunday, 24 February 2008, 07:54
Andy_A	Thanks Jayenkai! I think there's a better way to simulate different tiles on the fly. I'll post the particulars in a separate thread. : [Edit] Whoops! My bad. The way your illustration indicates would definitely be faster. [Edit] Okay then here's a technique you can use in to generate a nearly infinite number of colored tiles in a game. Create a base tile which you use to overlay the alpha'd shadows/textures. Then using the "Fast Color Replacement" algo (https://socoder.net/index.php?snippet=12528), you generate a working copy of the "base" tile with overlays with any color you want!

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