Initial data commit

Task/Xiaolin-Wus-line-algorithm/Yabasic/xiaolin-wus-line-algorithm.basic

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+bresline = false   // space toggles, for comparison
+
+rB = 255 : gB = 255 : bB = 224
+rL = 0 : gL = 0 : bL = 255
+
+sub round(x)
+    return int(x + .5)
+end sub
+
+sub plot(x, y, c, steep)
+//  plot the pixel at (x, y) with brightness c (where 0 <= c <= 1)
+
+    local t, C
+
+    if steep then t = x : x = y : y = t end if
+    C = 1 - c
+    color rL * c + rB * C, gL * c + gB * C, bL * c + bB * C
+
+    dot x, y
+end sub
+
+sub plot2(x, y, f, xgap, steep)
+    plot(x, y, (1 - f) * xgap, steep)
+    plot(x, y + 1, f * xgap, steep)
+end sub
+
+sub draw_line(x0, y0, x1, y1)
+    local steep, t, dx, dy, gradient, xend, yend, xgap, xpxl1, ypxl1, xpxl2, ypxl2, intery
+
+    if bresline then
+        line x0, y0, x1, y1
+        return
+    end if
+    steep = abs(y1 - y0) > abs(x1 - x0)
+    if steep then
+        t = x0 : x0 = y0 : y0 = t
+        t = x1 : x1 = y1 : y1 = t
+    end if
+    if x0 > x1 then
+        t = x0 : x0 = x1 : x1 = t
+        t = y0 : y0 = y1 : y1 = t
+    end if
+
+    dx = x1 - x0
+    dy = y1 - y0
+    if dx = 0 then
+        gradient = 1
+    else
+        gradient = dy / dx
+    end if
+
+    // handle first endpoint
+    xend = round(x0)
+    yend = y0 + gradient * (xend - x0)
+    xgap = 1 - frac(x0 + 0.5)
+    xpxl1 = xend // this will be used in the main loop
+    ypxl1 = int(yend)
+    plot2(xpxl1, ypxl1, frac(yend), xgap, steep)
+    intery = yend + gradient // first y-intersection for the main loop
+
+    // handle second endpoint
+    xend = round(x1)
+    yend = y1 + gradient * (xend - x1)
+    xgap = frac(x1 + 0.5)
+    xpxl2 = xend // this will be used in the main loop
+    ypxl2 = int(yend)
+    plot2(xpxl2, ypxl2, frac(yend), xgap, steep)
+
+    // main loop
+    for x = xpxl1 + 1 to xpxl2 - 1
+        plot2(x, int(intery), frac(intery), 1, steep)
+        intery = intery + gradient
+    next x
+end sub
+
+w = 640 : h = 480
+open window w, h
+
+color 0, 0, 255
+
+draw_line(0, 0, 200, 200)
+draw_line(w, 0, 200, 200)
+draw_line(0, h, 200, 200)
+draw_line(w, h, 200, 200)