Ok, this question turned out to be difficult. When Linux renders a non-implemented glyph from a font (at least in PyGame), you get an empty "border rectangle". This rectangle sits at base-line of the font, with space on either side, but no space at the top. Probably it's similar on other operating environments. (Originally I assumed the border surrounded the glyph-image without space, and was easily detected.)
So now we can check the glyph renders to something by examining the interior quarter of the glyph to see if it contains any non-empty pixels.
Obviously this is a heuristic, and may fail on characters like , which is mostly a descender. However I tested it on a bunch of symbol and Greek letters, and it seems to work OK. It does work for the OP's test glyph.
Instead of intensively examining every pixel, the algorithm first tries to check the centre horizontal pixels, then the centre vertical pixels. If neither of these produce a result, then every interior pixel is checked. If ever a pixel is found, we stop checking and return.
def glyphInFont( glyph, font ):
""" Given a glyph and a font, use a pixel-finding heuristic to determine
if the glyph renders to something other than an "empty border" non-existant
font symbol. Returns True if it renders to something. """
result = False
WHITE = ( 255, 255, 255 ) # can be any colour pair with constrast
BLACK = ( 0, 0, 0 )
try:
text_image = font.render( glyph, True, WHITE, BLACK )
text_rect = text_image.get_rect()
x_centre = text_rect.width // 2
y_centre = text_rect.height // 2
# On Linux at least, non-renderable glyphs have a border.
# work out a 50% search box, centred inside the gluph
box_top = y_centre - ( text_rect.height // 4 )
box_bottom = y_centre + ( text_rect.height // 4 )
box_left = x_centre - ( text_rect.width // 4 )
box_right = x_centre + ( text_rect.width // 4 )
# Trace a Horizontal line through the middle of the bitmap
# looking for non-black pixels
for x in range( box_left, box_right ):
if ( text_image.get_at( ( x, y_centre ) ) != BLACK ):
result = True
break
# If not found already, trace a line vertically
if ( result == False ):
for y in range( box_top, box_bottom ):
if ( text_image.get_at( ( x_centre, y ) ) != BLACK ):
result = True
break
# If still not found, check every pixel in the centre-box
if ( result == False ):
for y in range( box_top, box_bottom ):
for x in range( box_left, box_right ):
if ( text_image.get_at( ( x, y ) ) != BLACK ):
result = True
break
except UnicodeError as uce:
# Glyph-ID not supported
pass # False goes through
return result
Tested with the "Badboom" font, and whatever the Linux default SysFont is.
This reference program checks to see if the glyph renders in the given fonts, drawing it if True, otherwise drawing an "x".
import pygame
# Window size
WINDOW_WIDTH = 400
WINDOW_HEIGHT = 400
WINDOW_SURFACE = pygame.HWSURFACE|pygame.DOUBLEBUF|pygame.RESIZABLE
DARK_BLUE = ( 3, 5, 54 )
YELLOW = ( 255, 255, 0 )
RED = ( 255, 0, 0 )
symbols = [ '⊕', 'Δ', 'Ψ', '' ]
def glyphInFont( glyph, font ):
""" Given a glyph and a font, use a pixel-finding heuristic to determine
if the glyph renders to something other than an "empty border" non-existant
font symbol. Returns True if it renders to something. """
result = False
WHITE = ( 255, 255, 255 ) # can be any colour pair with constrast
BLACK = ( 0, 0, 0 )
try:
text_image = font.render( glyph, True, WHITE, BLACK )
text_rect = text_image.get_rect()
x_centre = text_rect.width // 2
y_centre = text_rect.height // 2
# On Linux at least, non-renderable glyphs have a border.
# work out a 50% search box, centred inside the gluph
box_top = y_centre - ( text_rect.height // 4 )
box_bottom = y_centre + ( text_rect.height // 4 )
box_left = x_centre - ( text_rect.width // 4 )
box_right = x_centre + ( text_rect.width // 4 )
# Trace a Horizontal line through the middle of the bitmap
# looking for non-black pixels
for x in range( box_left, box_right ):
if ( text_image.get_at( ( x, y_centre ) ) != BLACK ):
result = True
break
# If not found already, trace a line vertically
if ( result == False ):
for y in range( box_top, box_bottom ):
if ( text_image.get_at( ( x_centre, y ) ) != BLACK ):
result = True
break
# If still not found, check every pixel in the centre-box
if ( result == False ):
for y in range( box_top, box_bottom ):
for x in range( box_left, box_right ):
if ( text_image.get_at( ( x, y ) ) != BLACK ):
result = True
break
except UnicodeError as uce:
# Glyph-ID not supported
pass # False goes through
return result
### initialisation
pygame.init()
pygame.mixer.init()
window = pygame.display.set_mode( ( WINDOW_WIDTH, WINDOW_HEIGHT ), WINDOW_SURFACE )
pygame.display.set_caption("Glyph Check")
### Make some fonts
font1 = pygame.font.Font( 'badaboom.ttf', 64 ) # ref: https://www.1001freefonts.com/badaboom.font
font2 = pygame.font.SysFont( None, 64 )
### Main Loop
clock = pygame.time.Clock()
done = False
while not done:
# Handle user-input
for event in pygame.event.get():
if ( event.type == pygame.QUIT ):
done = True
# Update the window, but not more than 60fps
window.fill( DARK_BLUE )
# Simply to layout nicely on the screen
cursor_x = 50
cursor_y = (WINDOW_HEIGHT // 2 ) - 100
# Loop through the symbol list, rendering the symbol if it exists
# or an "x" otherwise
#
# NOTE: This is inefficiant demo code!
# It's bad to keep rendering fonts every frame
for glyph in symbols:
cursor_x += 50
if ( glyphInFont( glyph, font1 ) ):
window.blit( font1.render( glyph, True, YELLOW ), ( cursor_x, cursor_y ) )
else:
# does not exist
window.blit( font1.render( 'x', True, YELLOW ), ( cursor_x, cursor_y ) )
if ( glyphInFont( glyph, font2 ) ):
window.blit( font2.render( glyph, True, YELLOW ), ( cursor_x, cursor_y+100 ) )
else:
# does not exist
window.blit( font2.render( 'x', True, YELLOW ), ( cursor_x, cursor_y+100 ) )
pygame.display.flip()
# Clamp FPS
clock.tick( 3 ) # slow update
pygame.quit()
Note that the "happy poo" emoji glyph [] doesn't seem to work in either font, and causes an exception in font.render(), which is caught and considered a Fail.
