September 2017 Update

Task/Xiaolin-Wus-line-algorithm/Swift/xiaolin-wus-line-algorithm.swift

@@ -0,0 +1,93 @@
+import Darwin
+// apply pixel of color at x,y with an OVER blend to the bitmap
+public func pixel(color: Color, x: Int, y: Int) {
+    let idx = x + y * self.width
+    if idx >= 0 && idx < self.bitmap.count {
+        self.bitmap[idx] = self.blendColors(bot: self.bitmap[idx], top: color)
+    }
+}
+
+// return the fractional part of a Double
+func fpart(_ x: Double) -> Double {
+    return modf(x).1
+}
+
+// reciprocal of the fractional part of a Double
+func rfpart(_ x: Double) -> Double {
+    return 1 - fpart(x)
+}
+
+// draw a 1px wide line using Xiolin Wu's antialiased line algorithm
+public func smoothLine(_ p0: Point, _ p1: Point) {
+    var x0 = p0.x, x1 = p1.x, y0 = p0.y, y1 = p1.y //swapable ptrs
+    let steep = abs(y1 - y0) > abs(x1 - x0)
+    if steep {
+        swap(&x0, &y0)
+        swap(&x1, &y1)
+    }
+    if x0 > x1 {
+        swap(&x0, &x1)
+        swap(&y0, &y1)
+    }
+    let dX = x1 - x0
+    let dY = y1 - y0
+
+    var gradient: Double
+    if dX == 0.0 {
+        gradient = 1.0
+    }
+    else {
+        gradient = dY / dX
+    }
+
+    // handle endpoint 1
+    var xend = round(x0)
+    var yend = y0 + gradient * (xend - x0)
+    var xgap = self.rfpart(x0 + 0.5)
+    let xpxl1 = Int(xend)
+    let ypxl1 = Int(yend)
+
+    // first y-intersection for the main loop
+    var intery = yend + gradient
+
+    if steep {
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(yend) * xgap), x: ypxl1, y: xpxl1)
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(yend) * xgap), x: ypxl1 + 1, y: xpxl1)
+    }
+    else {
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(yend) * xgap), x: xpxl1, y: ypxl1)
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(yend) * xgap), x: xpxl1, y: ypxl1 + 1)
+    }
+
+    xend = round(x1)
+    yend = y1 + gradient * (xend - x1)
+    xgap = self.fpart(x1 + 0.5)
+    let xpxl2 = Int(xend)
+    let ypxl2 = Int(yend)
+
+    // handle second endpoint
+    if steep {
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(yend) * xgap), x: ypxl2, y: xpxl2)
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(yend) * xgap), x: ypxl2 + 1, y: xpxl2)
+    }
+    else {
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(yend) * xgap), x: xpxl2, y: ypxl2)
+        self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(yend) * xgap), x: xpxl2, y: ypxl2 + 1)
+    }
+
+    // main loop
+    if steep {
+        for x in xpxl1+1..<xpxl2 {
+            self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(intery)), x: Int(intery), y: x)
+            self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(intery)), x: Int(intery) + 1, y:x)
+            intery += gradient
+        }
+    }
+    else {
+        for x in xpxl1+1..<xpxl2 {
+            self.pixel(color: self.strokeColor.colorWithAlpha(self.rfpart(intery)), x: x, y: Int(intery))
+            self.pixel(color: self.strokeColor.colorWithAlpha(self.fpart(intery)), x: x, y: Int(intery) + 1)
+            intery += gradient
+        }
+    }
+}