This is a simple implementation of Xiaolin Wu’s line algorithm It doesn’t support colors or blending at all, but it should be a good starting point for anyone willing to implement proper AA lines in PB.
The code:
EnableExplicit Procedure.f trunc(X.f) ProcedureReturn Int(X) EndProcedure Procedure.f frac(X.f) ProcedureReturn (X - trunc(X)) EndProcedure Procedure.f invfrac(X.f) ProcedureReturn (1.0 - frac(X)) EndProcedure Procedure.i DrawPixel( x.i, y.i, color.i ) Plot( x, y, RGB(color, color, color) ) ; you would need to perform bound checking in here, or use your own plotting routine... EndProcedure Procedure WuLine( x1.f, y1.f, x2.f, y2.f) Define.i MaxPixelValue = 255 Define.f grad, xd, yd, length, xm, ym, xgap, ygap, xend, yend, xf, yf, brightness1, brightness2 Define.i x, y, ix1, ix2, iy1, iy2 Define.b c1, c2 xd = (x2-x1) yd = (y2-y1) If Abs(xd) > Abs(yd) ;-------------------- Horizontal -------------------- If x1 > x2 Swap x1, x2 Swap y1, y2 xd = (x2-x1) yd = (y2-y1) EndIf grad = yd/xd xend = trunc(x1+0.5) yend = y1 + grad*(xend-x1) xgap = invfrac(x1+0.5) ix1 = Int(xend) iy1 = Int(yend) brightness1 = invfrac(yend) * xgap brightness2 = frac(yend) * xgap c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(ix1,iy1, c1) DrawPixel(ix1,iy1+1, c2) yf = yend+grad xend = trunc(x2+0.5) yend = y2 + grad*(xend-x2) xgap = invfrac(x2-0.5) ix2 = Int(xend) iy2 = Int(yend) brightness1 = invfrac(yend) * xgap brightness2 = frac(yend) * xgap c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(ix2,iy2, c1 ) DrawPixel(ix2,iy2+1, c2) For x= (ix1+1) To (ix2-1) brightness1 = invfrac(yf) brightness2 = frac(yf) c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(x,Int(yf), c1 ) DrawPixel(x,Int(yf)+1, c2) yf = yf + grad Next Else ;-------------------- Vertical -------------------- If y1 > y2 Swap x1, x2 Swap y1, y2 xd = (x2-x1) yd = (y2-y1) EndIf grad = xd/yd yend = trunc(y1+0.5) xend = x1 + grad*(yend-y1) ygap = invfrac(y1+0.5) ix1 = Int(xend) iy1 = Int(yend) brightness1 = invfrac(xend) * ygap brightness2 = frac(xend) * ygap c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(ix1,iy1, c1) DrawPixel(ix1,iy1+1, c2) xf = xend+grad yend = trunc(y2+0.5) xend = x2 + grad*(yend-y2) ygap = invfrac(y2-0.5) ix2 = Int(xend) iy2 = Int(yend) brightness1 = invfrac(xend) * ygap brightness2 = frac(xend) * ygap c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(ix2,iy2, c1 ) DrawPixel(ix2,iy2+1, c2) For y= (iy1+1) To (iy2-1) brightness1 = invfrac(xf) brightness2 = frac(xf) c1 = (brightness1 * MaxPixelValue) c2 = (brightness2 * MaxPixelValue) DrawPixel(Int(xf),y, c1 ) DrawPixel(Int(xf)+1,y, c2) xf = xf + grad Next EndIf EndProcedure
You'll quickly notice there's no coloring and no blending, ie. lines that overlap each other are not blended; we would have to sample the frame buffer to do this and quite frankly, I'd rather use OpenGL if I needed to draw hundredths of AA lines.
There’s at least one issue with this code, sometimes the start/end points are drawn with an offset, etc. I don’t really have time to hunt down the bug though, but heres a quick and dirty example:
Macro RAD2DEG(_n_) : (_n_ * 57.295779513082323 ) : EndMacro Macro DEG2RAD(_n_) : (_n_ * 0.0174532925199432 ) : EndMacro Procedure.i render( img.i ) Define.f scalar = 240 Define.i ot, nt, theta, x, y Define.f t, time,frames Define.i mode = 1 InitKeyboard() Repeat If StartDrawing(ImageOutput(img)) Box(0,0,512,512, 0) If ExamineKeyboard() ; who would've guessed, this works fine without openscreen() if we're not in debug mode... If KeyboardReleased( #PB_Key_Space ) mode = 1 - mode EndIf EndIf For theta=0 To 360 Step 8 t = DEG2RAD(theta)+(frames*0.005) x = ( Cos(t) * scalar ) + 16 y = ( Sin(t) * scalar ) + 16 If mode WuLine( scalar+y*time*2, scalar+x*time*2, scalar+x, scalar+y ) Else LineXY( scalar+y*time*2, scalar+x*time*2, scalar+x, scalar+y, $ffffff ) EndIf Next time + (Cos(frames*0.01)*0.0045) frames + 1 StopDrawing() SetGadgetState( 0, ImageID(img) ) EndIf Delay(8) ForEver EndProcedure Define.i img If OpenWindow(0, 0, 0, 512, 512, "WuLine 4.50 by GuShH", #PB_Window_SystemMenu | #PB_Window_ScreenCentered) img = CreateImage(#PB_Any, 512, 512) If img CreateThread(@render(), img) EndIf ImageGadget(0, 0, 0, 0, 0, ImageID(img)) Repeat Until WaitWindowEvent(16) = #PB_Event_CloseWindow EndIf
Either way, enjoy.
PS: You may find the complete source in here