Simplify code by using supersampling for diagonal lines as well

Wu antialiasing obviously performs better but since characters are
rendered only once and are very small in pixel size, performance is
irrelevant here.

kitty/fonts/box_drawing.py

@@ -162,18 +162,22 @@ def downsample(src: BufType, dest: BufType, dest_width: int, dest_height: int, f
     for y in range(dest_height):
         offset = dest_width * y
         for x in range(dest_width):
-            dest[offset + x] = average_intensity_in_src(x, y)
+            dest[offset + x] = min(255, dest[offset + x] + average_intensity_in_src(x, y))
 
 
 def supersampled(supersample_factor: int = 4) -> Callable:
     # Anti-alias the drawing performed by the wrapped function by
     # using supersampling
 
+    class SSByteArray(bytearray):
+        supersample_factor = 1
+
     def create_wrapper(f: Callable) -> Callable:
         @wraps(f)
         def supersampled_wrapper(buf: BufType, width: int, height: int, *args: Any, **kw: Any) -> None:
             w, h = supersample_factor * width, supersample_factor * height
-            ssbuf = bytearray(w * h)
+            ssbuf = SSByteArray(w * h)
+            ssbuf.supersample_factor = supersample_factor
             f(ssbuf, w, h, *args, **kw)
             downsample(ssbuf, buf, width, height, factor=supersample_factor)
         return supersampled_wrapper
@@ -227,85 +231,37 @@ def corner_triangle(buf: BufType, width: int, height: int, corner: str) -> None:
     fill_region(buf, width, height, xlimits)
 
 
-def antialiased_1px_line(buf: BufType, width: int, height: int, p1: Tuple[int, int], p2: Tuple[int, int]) -> None:
+def thick_line(buf: BufType, width: int, height: int, thickness_in_pixels: int, p1: Tuple[int, int], p2: Tuple[int, int]) -> None:
-    # Draw an antialiased line using the Wu algorithm
+    if p1[0] > p2[0]:
-    x1, y1 = p1
+        p1, p2 = p2, p1
-    x2, y2 = p2
+    leq = line_equation(*p1, *p2)
-    dx, dy = x2 - x1, y2 - y1
+    for x in range(p1[0], p2[0] + 1):
-    off_limit = height * width
+        if 0 <= x < width:
-    steep = abs(dx) < abs(dy)
+            y_p = leq(x)
-
+            if thickness_in_pixels <= 1:
-    if steep:
+                r = range(int(y_p), int(y_p) + 1)
-        x1, y1, x2, y2, dx, dy = y1, x1, y2, x2, dy, dx
+            else:
-
+                delta = thickness_in_pixels // 2
-        def p(x: int, y: int) -> Tuple[int, int]:
+                r = range(int(y_p) - delta, int(y_p) + delta + (thickness_in_pixels % 2))
-            return y, x
+            for y in r:
-    else:
+                if 0 <= y < height:
-        def p(x: int, y: int) -> Tuple[int, int]:
+                    buf[x + y * width] = 255
-            return x, y
-
-    if x2 < x1:
-        x1, x2, y1, y2 = x2, x1, y2, y1
-
-    def fpart(x: float) -> float:
-        return x - int(x)
-
-    def rfpart(x: float) -> float:
-        return 1 - fpart(x)
-
-    def putpixel(p: Tuple[int, int], alpha: float) -> None:
-        x, y = p
-        off = int(x + y * width)
-        if 0 <= off < off_limit:
-            buf[off] = int(min(buf[off] + (alpha * 255), 255))
-
-    def draw_endpoint(pt: Tuple[int, int]) -> int:
-        x, y = pt
-        xend = round(x)
-        yend = y + grad * (xend - x)
-        xgap = rfpart(x + 0.5)
-        px, py = int(xend), int(yend)
-        putpixel(p(px, py), rfpart(yend) * xgap)
-        putpixel(p(px, py+1), fpart(yend) * xgap)
-        return px
-
-    grad = dy/dx
-    intery = y1 + rfpart(x1) * grad
-
-    xstart = draw_endpoint(p(*p1))
-    xend = draw_endpoint(p(*p2))
-
-    if xstart > xend:
-        xstart, xend = xend, xstart
-    xstart += 1
-
-    for x in range(xstart, xend):
-        y = int(intery)
-        putpixel(p(x, y), rfpart(intery))
-        putpixel(p(x, y+1), fpart(intery))
-        intery += grad
-
-
-def antialiased_line(buf: BufType, width: int, height: int, p1: Tuple[int, int], p2: Tuple[int, int], level: int = 1) -> None:
-    th = thickness(level)
-    if th < 2:
-        return antialiased_1px_line(buf, width, height, p1, p2)
-    (x1, y1), (x2, y2) = p1, p2
-    dh = th // 2
-    items = range(-dh, dh + (th % 2))
-    for delta in items:
-        antialiased_1px_line(buf, width, height, (x1, y1 + delta), (x2, y2 + delta))
 
 
+@supersampled()
 def cross_line(buf: BufType, width: int, height: int, left: bool = True, level: int = 1) -> None:
     if left:
         p1, p2 = (0, 0), (width - 1, height - 1)
     else:
         p1, p2 = (width - 1, 0), (0, height - 1)
-    antialiased_line(buf, width, height, p1, p2, level=level)
+    supersample_factor = getattr(buf, 'supersample_factor')
+    thick_line(buf, width, height, supersample_factor * thickness(level), p1, p2)
 
 
+@supersampled()
 def half_cross_line(buf: BufType, width: int, height: int, which: str = 'tl', level: int = 1) -> None:
+    supersample_factor = getattr(buf, 'supersample_factor')
+    thickness_in_pixels = thickness(level) * supersample_factor
     my = (height - 1) // 2
     if which == 'tl':
         p1 = 0, 0
@@ -319,7 +275,7 @@ def half_cross_line(buf: BufType, width: int, height: int, which: str = 'tl', le
     else:
         p2 = width - 1, height - 1
         p1 = 0, my
-    antialiased_line(buf, width, height, p1, p2, level=level)
+    thick_line(buf, width, height, thickness_in_pixels, p1, p2)
 
 
 BezierFunc = Callable[[float], float]