macos - 为什么 TrueType 字体在 Mac 上仅使用 "Quadratic Curves"？

Question

我使用下面的代码提取了 TrueType 字体的路径元素。

问题在于 element->type 描述的曲线仅属于 kCGPathElementAddQuadCurveToPoint 类型，该类型有 2 个点(低质量)。为什么没有任何元素使用更高质量的 kCGPathElementAddCurveToPoint 类型(有 3 个点)？

有人有想法吗？

int count = 0;
void applierFunction(void *info, const CGPathElement *element)
{
    int point_count;
    switch (element->type)
    {
        case kCGPathElementMoveToPoint:
            point_count = 1;
            break;
        case kCGPathElementAddLineToPoint:
            point_count = 1;
            break;
        case kCGPathElementAddQuadCurveToPoint:
            point_count = 2;
            break;
        case kCGPathElementAddCurveToPoint:
            point_count = 3;
            break;
        case kCGPathElementCloseSubpath:
            point_count = 0;
            break;
    }
    count+=point_count;
    printf("%u.:\n", count);
    for (int i = 0; i<point_count; i++) {
        switch (element->type) {
            case kCGPathElementMoveToPoint:
                printf("kCGPathElementMoveToPoint\n");
                break;
            case kCGPathElementAddLineToPoint:
                printf("kCGPathElementAddLineToPoint\n");
                break;
            case kCGPathElementAddQuadCurveToPoint:
                printf("kCGPathElementAddQuadCurveToPoint\n");
                break;
            case kCGPathElementAddCurveToPoint:
                printf("kCGPathElementAddCurveToPoint\n");
                break;
            case kCGPathElementCloseSubpath:
                printf("kCGPathElementCloseSubpath\n");
                break;
            default:
                printf("unknown path type\n");
        }
    }
}

void extractStringPathElements()
{
    CFStringRef str = CFSTR("Q");
    CFStringRef strFont = CFSTR("Arial");
    CTFontRef font = CTFontCreateWithName(strFont, 500, NULL);
    CFStringRef keys[] = {kCTFontAttributeName};
    CFTypeRef values[] = {font};
    CFDictionaryRef attr = CFDictionaryCreate(NULL, (const void **)&keys,
                                                (const void **)&values, sizeof(keys) / sizeof(keys[0]),
                                                &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    CFAttributedStringRef attrString =
    CFAttributedStringCreate(NULL, str, attr);
    CFRelease(attr);
    CTLineRef line = CTLineCreateWithAttributedString(attrString);
    CFArrayRef runs = CTLineGetGlyphRuns(line);
    long runCount = CFArrayGetCount(runs);
    for (int ri = 0; ri < runCount; ri++) {
        ::CTRunRef run = (::CTRunRef)CFArrayGetValueAtIndex(runs, ri);
        long glyphCount = CTRunGetGlyphCount(run);
        const unsigned short *glyphs = CTRunGetGlyphsPtr(run);
        for (int gi = 0; gi < glyphCount; gi++) {
            ::CGPathRef path = CTFontCreatePathForGlyph(font, glyphs[gi], NULL);
            CGPathApply(path, 0, applierFunction);
            printf("glyph %u has %u elements.\n", glyphs[gi], count);
            CGPathRelease(path);
        }
    }
    CFRelease(line);
    CFRelease(attrString);
    CFRelease(font);

}

int main (int argc, const char * argv[])
{
    extractStringPathElements();
    return 0;
}

Answer 1

TrueType 没有三次贝塞尔曲线。它仅限于二次贝塞尔曲线。 TrueType 就是这样指定的。