def _opengl_context():
"""Assure we are running with a valid OpenGL context.
Only create a Canvas is one doesn't exist. Creating and closing a
Canvas causes vispy to process Qt events which can cause problems.
Ideally call opengl_context() on start after creating your first
Canvas. However it will work either way.
"""
canvas = Canvas(show=False) if get_current_canvas() is None else None
try:
yield
finally:
if canvas is not None:
canvas.close()
def _text_to_vbo(text, font, anchor_x, anchor_y, lowres_size):
"""Convert text characters to VBO"""
# Necessary to flush commands before requesting current viewport because
# There may be a set_viewport command waiting in the queue.
# TODO: would be nicer if each canvas just remembers and manages its own
# viewport, rather than relying on the context for this.
canvas = context.get_current_canvas()
canvas.context.flush_commands()
text_vtype = np.dtype([('a_position', np.float32, 2),
('a_texcoord', np.float32, 2)])
vertices = np.zeros(len(text) * 4, dtype=text_vtype)
prev = None
width = height = ascender = descender = 0
ratio, slop = 1. / font.ratio, font.slop
x_off = -slop
# Need to make sure we have a unicode string here (Py2.7 mis-interprets
# characters like "•" otherwise)
if sys.version[0] == '2' and isinstance(text, str):
text = text.decode('utf-8')
# Need to store the original viewport, because the font[char] will
# trigger SDF rendering, which changes our viewport
# todo: get rid of call to glGetParameter!
# Also analyse chars with large ascender and descender, otherwise the
# vertical alignment can be very inconsistent
for char in 'hy':
glyph = font[char]
y0 = glyph['offset'][1] * ratio + slop
y1 = y0 - glyph['size'][1]
ascender = max(ascender, y0 - slop)
descender = min(descender, y1 + slop)
height = max(height, glyph['size'][1] - 2 * slop)
# Get/set the fonts whitespace length and line height (size of this ok?)
glyph = font[' ']
spacewidth = glyph['advance'] * ratio
lineheight = height * 1.5
# Added escape sequences characters: {unicode:offset,...}
# ord('\a') = 7
# ord('\b') = 8
# ord('\f') = 12
# ord('\n') = 10 => linebreak
# ord('\r') = 13
# ord('\t') = 9 => tab, set equal 4 whitespaces?
# ord('\v') = 11 => vertical tab, set equal 4 linebreaks?
# If text coordinate offset > 0 -> it applies to x-direction
# If text coordinate offset < 0 -> it applies to y-direction
esc_seq = {7: 0, 8: 0, 9: -4, 10: 1, 11: 4, 12: 0, 13: 0}
# Keep track of y_offset to set lines at right position
y_offset = 0
# When a line break occur, record the vertices index value
vi_marker = 0
ii_offset = 0 # Offset since certain characters won't be drawn
# The running tracker of characters vertex index
vi = 0
orig_viewport = canvas.context.get_viewport()
for ii, char in enumerate(text):
if ord(char) in esc_seq:
if esc_seq[ord(char)] < 0:
# Add offset in x-direction
x_off += abs(esc_seq[ord(char)]) * spacewidth
width += abs(esc_seq[ord(char)]) * spacewidth
elif esc_seq[ord(char)] > 0:
# Add offset in y-direction and reset things in x-direction
dx = dy = 0
if anchor_x == 'right':
dx = -width
elif anchor_x == 'center':
dx = -width / 2.
vertices['a_position'][vi_marker:vi + 4] += (dx, dy)
vi_marker = vi + 4
ii_offset -= 1
# Reset variables that affects x-direction positioning
x_off = -slop
width = 0
# Add offset in y-direction
y_offset += esc_seq[ord(char)] * lineheight
else:
# For ordinary characters, normal procedure
glyph = font[char]
kerning = glyph['kerning'].get(prev, 0.) * ratio
x0 = x_off + glyph['offset'][0] * ratio + kerning
y0 = glyph['offset'][1] * ratio + slop - y_offset
x1 = x0 + glyph['size'][0]
y1 = y0 - glyph['size'][1]
u0, v0, u1, v1 = glyph['texcoords']
position = [[x0, y0], [x0, y1], [x1, y1], [x1, y0]]
texcoords = [[u0, v0], [u0, v1], [u1, v1], [u1, v0]]
vi = (ii + ii_offset) * 4
vertices['a_position'][vi:vi + 4] = position
vertices['a_texcoord'][vi:vi + 4] = texcoords
x_move = glyph['advance'] * ratio + kerning
x_off += x_move
ascender = max(ascender, y0 - slop)
descender = min(descender, y1 + slop)
width += x_move
height = max(height, glyph['size'][1] - 2 * slop)
prev = char
if orig_viewport is not None:
canvas.context.set_viewport(*orig_viewport)
dx = dy = 0
if anchor_y == 'top':
dy = -descender
elif anchor_y in ('center', 'middle'):
dy = (-descender - ascender) / 2
elif anchor_y == 'bottom':
dy = -ascender
if anchor_x == 'right':
dx = -width
elif anchor_x == 'center':
dx = -width / 2.
# If any linebreaks occured in text, we only want to translate characters
# in the last line in text (those after the vi_marker)
vertices['a_position'][0:vi_marker] += (0, dy)
vertices['a_position'][vi_marker:] += (dx, dy)
vertices['a_position'] /= lowres_size
return vertices
