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Task/Xiaolin-Wus-line-algorithm/FreeBASIC/xiaolin-wus-line-algorithm.freebasic

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+' version 21-06-2015
+' compile with: fbc -s console or fbc -s gui
+' Xiaolin Wu’s line-drawing algorithm
+'shared var and macro's
+
+Dim Shared As UInteger wu_color
+
+#Macro ipart(x)
+Int(x)             ' integer part
+#EndMacro
+
+#Macro round(x)
+Int((x) + .5)      ' round off
+#EndMacro
+
+#Macro fpart(x)
+Frac(x)            ' fractional part
+#EndMacro
+
+#Macro rfpart(x)
+' 1 - Frac(x)    ' seems to give problems for very small x
+IIf(1 - Frac(x) >= 1, 1, 1 - Frac(x))
+#EndMacro
+
+#Macro plot(x, y , c)
+' use the alpha channel to set the amount of color
+PSet(x,y), wu_color Or (Int(c * 255)) Shl 24
+#EndMacro
+
+Sub drawline(x0 As Single, y0 As Single, x1 As Single, y1 As Single,_
+    col As UInteger = RGB(255,255,255))
+
+    wu_color = col And &HFFFFFF ' strip off the alpha channel information
+
+    Dim As Single gradient
+    Dim As Single xend, yend, xgap, intery
+    Dim As UInteger xpxl1, ypxl1, xpxl2, ypxl2, x
+    Dim As Integer steep = Abs(y1 - y0) > Abs(x1 - x0) ' boolean
+
+    If steep Then
+        Swap x0, y0
+        Swap x1, y1
+    End If
+
+    If x0 > x1 Then
+        Swap x0, x1
+        Swap y0, y1
+    End If
+
+    gradient = (y1 - y0) / (x1 - x0)
+
+    ' first endpoint
+    ' xend = round(x0)
+    xend = ipart(x0)
+    yend = y0 + gradient * (xend - x0)
+    xgap = rfpart(x0 + .5)
+    xpxl1 = xend              ' this will be used in the main loop
+    ypxl1 = ipart(yend)
+    If steep Then
+        plot(ypxl1,   xpxl1, rfpart(yend) * xgap)
+        plot(ypxl1+1, xpxl1,  fpart(yend) * xgap)
+    Else
+        plot(xpxl1, ypxl1,   rfpart(yend) * xgap)
+        plot(xpxl1, ypxl1+1,  fpart(yend) * xgap)
+    End If
+    intery = yend + gradient  ' first y-intersecction for the main loop
+
+    ' handle second endpoint
+    ' xend = round(x1)
+    xend = ipart(x1)
+    yend = y1 + gradient * (xend - x1)
+    xgap = fpart(x1 + .5)
+    xpxl2 = xend              ' this will be used in the main loop
+    ypxl2 = ipart(yend)
+    If steep Then
+        plot(ypxl2,   xpxl2, rfpart(yend) * xgap)
+        plot(ypxl2+1, xpxl2,  fpart(yend) * xgap)
+    Else
+        plot(xpxl2, ypxl2,   rfpart(yend) * xgap)
+        plot(xpxl2, ypxl2+1,  fpart(yend) * xgap)
+    End If
+
+    ' main loop
+    If steep Then
+        For x = xpxl1 + 1 To xpxl2 - 1
+            plot(ipart(intery),   x, rfpart(intery))
+            plot(ipart(intery)+1, x,  fpart(intery))
+            intery = intery + gradient
+        Next
+    Else
+        For x = xpxl1 + 1 To xpxl2 - 1
+            plot(x, ipart(intery),   rfpart(intery))
+            plot(x, ipart(intery)+1,  fpart(intery))
+            intery = intery + gradient
+        Next
+    End If
+
+End Sub
+
+' ------=< MAIN >=------
+
+#Define W_  600
+#Define H_  600
+
+#Include Once "fbgfx.bi"   ' needed setting the screen attributes
+Dim As Integer i
+Dim As String fname = __FILE__
+
+ScreenRes W_, H_, 32,, FB.GFX_ALPHA_PRIMITIVES
+
+Randomize Timer
+
+For i = 0 To H_ Step H_\30
+    drawline(0, 0, W_, i, Int(Rnd * &HFFFFFF))
+Next
+
+For i = 0 To W_ Step W_\30
+    drawline(0, 0, i, H_, Int(Rnd * &HFFFFFF))
+Next
+
+i = InStr(fname,".bas")
+fname = Left(fname, Len(fname)-i+1)
+WindowTitle fname + "    hit any key to end program"
+
+While Inkey <> "" : Wend
+Sleep
+End