fonts - 如何确定字体是否支持字符

Question

我正在使用pygame，我想显示字符⊕，但是当我运行代码时，它显示的是一个矩形，我尝试了许多其他字体，它们都是矩形或带问号的矩形。其他特殊字符如 ± 有效，所以我不确定问题是什么。我搜索了一下，网站上还有另一个与此类似的问题，它说 python 3.x 对特殊字符没有问题，只要它们受字体支持。然后我检查了支持⊕的字体，大多数字体都支持。
tl;博士
你如何在pygame上显示⊕？

Answer 1

好吧，这个问题变得很困难。当 Linux 从字体(至少在 PyGame 中)呈现未实现的字形时，您会得到一个空的“边框矩形”。这个矩形位于字体的基线处，两边都有空间，但顶部没有空间。可能它在其他操作环境中类似。 (最初我假设边界围绕字形图像没有空间，并且很容易被检测到。)
所以现在我们可以通过检查字形的内部四分之一来检查字形渲染，看看它是否包含任何非空像素。
显然这是一种启发式方法，可能会在像 , 这样的字符上失败。这主要是一个下降者。但是我在一堆符号和希腊字母上测试了它，它似乎工作正常。它确实适用于 OP 的测试字形。
该算法不是集中检查每个像素，而是首先尝试检查中心水平像素，然后是中心垂直像素。如果这些都没有产生结果，则检查每个内部像素。如果找到像素，我们将停止检查并返回。

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

使用“ Badboom ”字体进行测试，无论 Linux 默认的 SysFont 是什么。

此引用程序检查字形是否以给定的字体呈现，如果为 True，则绘制它，否则绘制“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()

请注意，“happy poo”表情符号 [💩] 似乎不适用于任何一种字体，并导致 font.render() 中的异常，它被捕获并被视为失败。