Refactor the cell rendering code for greater re-use

Also start work on CoreText based rendering

kitty/fonts/render.py

@@ -2,9 +2,88 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
-from kitty.constants import isosx
+import ctypes
 
+from kitty.constants import isosx
+from .box_drawing import render_box_char, is_renderable_box_char
 if isosx:
-    from .core_text import set_font_family, render_cell  # noqa
+    from .core_text import set_font_family, render_cell as rc, current_cell  # noqa
 else:
-    from .freetype import set_font_family, render_cell  # noqa
+    from .freetype import set_font_family, render_cell as rc, current_cell  # noqa
+
+
+def add_line(buf, cell_width, position, thickness):
+    y = position - thickness // 2
+    while thickness:
+        thickness -= 1
+        offset = cell_width * y
+        for x in range(cell_width):
+            buf[offset + x] = 255
+        y += 1
+
+
+def add_curl(buf, cell_width, position, thickness):
+    for y in range(position - thickness, position):
+        for x in range(0, cell_width // 2):
+            offset = cell_width * y
+            buf[offset + x] = 255
+    for y in range(position, position + thickness):
+        for x in range(cell_width // 2, cell_width):
+            offset = cell_width * y
+            buf[offset + x] = 255
+
+
+def render_cell(text=' ', bold=False, italic=False, underline=0, strikethrough=False):
+    CharTexture, cell_width, cell_height, baseline, underline_thickness, underline_position = current_cell()
+    if is_renderable_box_char(text):
+        first, second = render_box_char(text, CharTexture(), cell_width, cell_height), None
+    else:
+        first, second = rc(text, bold, italic)
+
+    def dl(f, *a):
+        f(first, cell_width, *a)
+        if second is not None:
+            f(second, cell_width, *a)
+
+    if underline:
+        t = underline_thickness
+        if underline == 2:
+            t = max(1, min(cell_height - underline_position - 1, t))
+        dl(add_curl if underline == 2 else add_line, underline_position, t)
+    if strikethrough:
+        pos = int(0.65 * baseline)
+        dl(add_line, pos, underline_thickness)
+
+    return first, second
+
+
+def join_cells(cell_width, cell_height, *cells):
+    dstride = len(cells) * cell_width
+    ans = (ctypes.c_ubyte * (cell_height * dstride))()
+    for r in range(cell_height):
+        soff = r * cell_width
+        doff = r * dstride
+        for cnum, cell in enumerate(cells):
+            doff2 = doff + (cnum * cell_width)
+            ans[doff2:doff2 + cell_width] = cell[soff:soff + cell_width]
+    return ans
+
+
+def display_bitmap(data, w, h):
+    from PIL import Image
+    img = Image.new('L', (w, h))
+    img.putdata(data)
+    img.show()
+
+
+def test_rendering(text='\'Ping👁a⧽', sz=144, family='Ubuntu Mono for Kovid'):
+    set_font_family(family, sz)
+    cells = []
+    for c in text:
+        f, s = render_cell(c, underline=2, strikethrough=True)
+        cells.append(f)
+        if s is not None:
+            cells.append(s)
+    cell_width, cell_height = current_cell()[1:3]
+    char_data = join_cells(cell_width, cell_height, *cells)
+    display_bitmap(char_data, cell_width * len(cells), cell_height)