Finish up Core Text based rendering

kitty/core_text.m

@@ -133,13 +133,13 @@ cell_size(Face *self) {
             if (w > width) width = w; 
         }
     }
-    return Py_BuildValue("I", width + 2);  // + 2 for antialiasing which needs pixels on either side
+    return Py_BuildValue("I", width);  
 #undef count
 }
 
 static PyObject*
 render_char(Face *self, PyObject *args) {
-#define render_char_doc ""
+#define render_char_doc "Render the specified character into the specified buffer. Combining unicode chars should be handled automatically (I hope)"
     char *s;
     unsigned int width, height;
     PyObject *pbuf;
@@ -168,10 +168,11 @@ render_char(Face *self, PyObject *args) {
     CGContextSetTextDrawingMode(ctx, kCGTextFill);
     CGGlyph glyph = glyphs[0];
     if (glyph) {
-        CGRect rect = CTFontGetBoundingRectsForGlyphs(font, kCTFontOrientationHorizontal, glyphs, 0, 1);
         // TODO: Scale the glyph if its bbox is larger than the image by using a non-identity transform
+        /* CGRect rect = CTFontGetBoundingRectsForGlyphs(font, kCTFontOrientationHorizontal, glyphs, 0, 1); */
         CGContextSetTextMatrix(ctx, transform);
-        CGFloat pos_x = -rect.origin.x + 1, pos_y = height - rect.origin.y - rect.size.height;
+        CGFloat leading = self->leading > 0 ? self->leading : 1;  // Ensure at least one pixel of leading so that antialiasing works at the left edge
+        CGFloat pos_x = leading, pos_y = height - self->ascent;  
         CGContextSetTextPosition(ctx, pos_x, pos_y);
         CTFontDrawGlyphs(font, &glyph, &CGPointZero, 1, ctx);
     }

kitty/fonts/core_text.py

@@ -22,11 +22,10 @@ def set_font_family(family, size_in_pts):
     mf = main_font[(False, False)]
     cell_width = mf.cell_size()
     cell_height = ceil_int(mf.ascent + mf.descent)
-    cell_height += 1 * int(round(dpi / 72.0))  # some line spacing
     CellTexture = ctypes.c_ubyte * (cell_width * cell_height)
     WideCellTexture = ctypes.c_ubyte * (2 * cell_width * cell_height)
     baseline = int(round(mf.ascent))
-    underline_position = int(round(mf.underline_position))
+    underline_position = int(round(baseline - mf.underline_position))
     underline_thickness = ceil_int(mf.underline_thickness)
     return cell_width, cell_height
 
@@ -35,6 +34,16 @@ def current_cell():
     return CellTexture, cell_width, cell_height, baseline, underline_thickness, underline_position
 
 
+def split(buf, cell_width, cell_height):
+    first, second = CellTexture(), CellTexture()
+    for y in range(cell_height):
+        offset, woffset = y * cell_width, y * cell_width * 2
+        for x in range(cell_width):
+            first[offset + x] = buf[woffset + x]
+            second[offset + x] = buf[woffset + cell_width + x]
+    return first, second
+
+
 def render_cell(text=' ', bold=False, italic=False):
     width = wcwidth(text[0])
     face = main_font[(bold, italic)]
@@ -43,15 +52,24 @@ def render_cell(text=' ', bold=False, italic=False):
     else:
         buf, width = CellTexture(), cell_width
     face.render_char(text, width, cell_height, ctypes.addressof(buf))
+    if width == 2:
+        first, second = split(buf, cell_width, cell_height)
+    else:
+        first, second = buf, None
+    return first, second
 
 
-def develop():
+def develop(sz=288):
+    import pickle
     from kitty.fast_data_types import glfw_init
+    from .render import render_string
     glfw_init()
-    set_font_family('monospace', 12.0)
+    set_font_family('monospace', sz)
     for (bold, italic), face in main_font.items():
         print('bold: {} italic: {} family:{} full name: {}'.format(bold, italic, face.family_name, face.full_name))
     f = main_font[(False, False)]
     for attr in 'units_per_em ascent descent leading underline_position underline_thickness scaled_point_sz'.split():
         print(attr, getattr(f, attr))
     print('cell_width: {}, cell_height: {}, baseline: {}'.format(cell_width, cell_height, baseline))
+    buf, w, h = render_string(sz=200)
+    open('/tmp/cell.data', 'wb').write(pickle.dumps((bytearray(buf), w, h)))

kitty/fonts/render.py

@@ -76,7 +76,7 @@ def display_bitmap(data, w, h):
     img.show()
 
 
-def test_rendering(text='\'Ping👁a⧽', sz=144, family='Ubuntu Mono for Kovid'):
+def render_string(text='\'Qing👁a⧽', sz=144, family='monospace'):
     set_font_family(family, sz)
     cells = []
     for c in text:
@@ -86,4 +86,8 @@ def test_rendering(text='\'Ping👁a⧽', sz=144, family='Ubuntu Mono for Kov
             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)
+    return char_data, cell_width * len(cells), cell_height
+
+
+def test_rendering(text='\'Ping👁a⧽', sz=144, family='monospace'):
+    display_bitmap(*render_string(text, sz, family))