光栅化
这里可能发生的事情是它决定必须将 textLayer 渲染为像素。注意shouldRasterize in the CALayer Class Reference 的警告：
当此属性的值为 NO 时，图层将尽可能直接合成到目标中。如果合成模型的某些特征（例如包含过滤器）需要，图层仍可以在合成之前进行光栅化。
因此，CATextLayer 可能会突然决定光栅化。如果它是旋转层的子层，它决定栅格化。所以，不要让这种情况发生。
单面层
这将带您回到导致文本反转的解决方案。您可以通过关闭文本图层上的doubleSided 来防止这种情况。您的标志现在将在远端为空白，因此添加第二个文本层，相对于第一个旋转 180 度。
声明两个文本层：
@property (retain) CAShapeLayer *pathLayer;
@property (retain) CATextLayer *textLayerFront;
@property (retain) CATextLayer *textLayerBack;
然后，将它们初始化为单面，背面旋转 180 度：
CAShapeLayer *pathLayer = [CAShapeLayer layer];
// Also need to store a UIBezierPath in the pathLayer.
CATextLayer *textLayerFront = [CATextLayer layer];
textLayerFront.doubleSided = NO;
textLayerFront.string = @"Front";
textLayerFront.contentsScale = [[UIScreen mainScreen] scale];
CATextLayer *textLayerBack = [CATextLayer layer];
textLayerBack.doubleSided = NO;
// Eventually both sides will have the same text, but for demonstration purposes we will label them differently.
textLayerBack.string = @"Back";
// Rotate the back layer 180 degrees relative to the front layer.
textLayerBack.transform = CATransform3DRotate(textLayerBack.transform, M_PI, 0, 1, 0);
textLayerBack.contentsScale = [[UIScreen mainScreen] scale];
// Make all the layers siblings. These means they must all be rotated independently of each other.
// The layers can flicker if their Z position is close to the background, so move them forward.
// This will not work if the main layer has a perspective transform on it.
textLayerFront.zPosition = 256;
textLayerBack.zPosition = 256;
// It would make sense to make the text layers siblings of the path layer, but this seems to mean they get pre-rendered, blurring them.
[self.layer addSublayer:pathLayer];
[self.layer addSublayer:textLayerBack];
[self.layer addSublayer:textLayerFront];
// Store the layers constructed at this time for later use.
[self setTextLayerFront:textLayerFront];
[self setTextLayerBack:textLayerBack];
[self setPathLayer:pathLayer];
然后您可以旋转图层。只要您始终旋转相同的量，它们就会显示正确。
CGFloat angle = M_PI;
self.pathLayer.transform = CATransform3DRotate(self.pathLayer.transform, angle, 0, 1, 0);
self.textLayerFront.transform = CATransform3DRotate(self.textLayerFront.transform, angle, 0, 1, 0);
self.textLayerBack.transform = CATransform3DRotate(self.textLayerBack.transform, angle, 0, 1, 0);
然后您应该会发现，您可以将标志旋转到任意角度，同时保持文字清晰。
文本到路径
如果您确实需要以导致 CATextLayer 光栅化的方式来操作文本显示，还有另一种选择：将文本转换为 UIBezierPath 表示。然后可以将其放置在 CAShapeLayer 中。这样做需要深入研究 Core Text，但结果是强大的。例如，您可以animate the text being drawn。
// - (UIBezierPath*) bezierPathWithString:(NSString*) string font:(UIFont*) font inRect:(CGRect) rect;
// Requires CoreText.framework
// This creates a graphical version of the input screen, line wrapped to the input rect.
// Core Text involves a whole hierarchy of objects, all requiring manual management.
- (UIBezierPath*) bezierPathWithString:(NSString*) string font:(UIFont*) font inRect:(CGRect) rect;
{
UIBezierPath *combinedGlyphsPath = nil;
CGMutablePathRef combinedGlyphsPathRef = CGPathCreateMutable();
if (combinedGlyphsPathRef)
{
// It would be easy to wrap the text into a different shape, including arbitrary bezier paths, if needed.
UIBezierPath *frameShape = [UIBezierPath bezierPathWithRect:rect];
// If the font name wasn't found while creating the font object, the result is a crash.
// Avoid this by falling back to the system font.
CTFontRef fontRef;
if ([font fontName])
fontRef = CTFontCreateWithName((__bridge CFStringRef) [font fontName], [font pointSize], NULL);
else if (font)
fontRef = CTFontCreateUIFontForLanguage(kCTFontUserFontType, [font pointSize], NULL);
else
fontRef = CTFontCreateUIFontForLanguage(kCTFontUserFontType, [UIFont systemFontSize], NULL);
if (fontRef)
{
CGPoint basePoint = CGPointMake(0, CTFontGetAscent(fontRef));
CFStringRef keys[] = { kCTFontAttributeName };
CFTypeRef values[] = { fontRef };
CFDictionaryRef attributesRef = CFDictionaryCreate(NULL, (const void **)&keys, (const void **)&values,
sizeof(keys) / sizeof(keys[0]), &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
if (attributesRef)
{
CFAttributedStringRef attributedStringRef = CFAttributedStringCreate(NULL, (__bridge CFStringRef) string, attributesRef);
if (attributedStringRef)
{
CTFramesetterRef frameSetterRef = CTFramesetterCreateWithAttributedString(attributedStringRef);
if (frameSetterRef)
{
CTFrameRef frameRef = CTFramesetterCreateFrame(frameSetterRef, CFRangeMake(0,0), [frameShape CGPath], NULL);
if (frameRef)
{
CFArrayRef lines = CTFrameGetLines(frameRef);
CFIndex lineCount = CFArrayGetCount(lines);
CGPoint lineOrigins[lineCount];
CTFrameGetLineOrigins(frameRef, CFRangeMake(0, lineCount), lineOrigins);
for (CFIndex lineIndex = 0; lineIndex<lineCount; lineIndex++)
{
CTLineRef lineRef = CFArrayGetValueAtIndex(lines, lineIndex);
CGPoint lineOrigin = lineOrigins[lineIndex];
CFArrayRef runs = CTLineGetGlyphRuns(lineRef);
CFIndex runCount = CFArrayGetCount(runs);
for (CFIndex runIndex = 0; runIndex<runCount; runIndex++)
{
CTRunRef runRef = CFArrayGetValueAtIndex(runs, runIndex);
CFIndex glyphCount = CTRunGetGlyphCount(runRef);
CGGlyph glyphs[glyphCount];
CGSize glyphAdvances[glyphCount];
CGPoint glyphPositions[glyphCount];
CFRange runRange = CFRangeMake(0, glyphCount);
CTRunGetGlyphs(runRef, CFRangeMake(0, glyphCount), glyphs);
CTRunGetPositions(runRef, runRange, glyphPositions);
CTFontGetAdvancesForGlyphs(fontRef, kCTFontDefaultOrientation, glyphs, glyphAdvances, glyphCount);
for (CFIndex glyphIndex = 0; glyphIndex<glyphCount; glyphIndex++)
{
CGGlyph glyph = glyphs[glyphIndex];
// For regular UIBezierPath drawing, we need to invert around the y axis.
CGAffineTransform glyphTransform = CGAffineTransformMakeTranslation(lineOrigin.x+glyphPositions[glyphIndex].x, rect.size.height-lineOrigin.y-glyphPositions[glyphIndex].y);
glyphTransform = CGAffineTransformScale(glyphTransform, 1, -1);
CGPathRef glyphPathRef = CTFontCreatePathForGlyph(fontRef, glyph, &glyphTransform);
if (glyphPathRef)
{
// Finally carry out the appending.
CGPathAddPath(combinedGlyphsPathRef, NULL, glyphPathRef);
CFRelease(glyphPathRef);
}
basePoint.x += glyphAdvances[glyphIndex].width;
basePoint.y += glyphAdvances[glyphIndex].height;
}
}
basePoint.x = 0;
basePoint.y += CTFontGetAscent(fontRef) + CTFontGetDescent(fontRef) + CTFontGetLeading(fontRef);
}
CFRelease(frameRef);
}
CFRelease(frameSetterRef);
}
CFRelease(attributedStringRef);
}
CFRelease(attributesRef);
}
CFRelease(fontRef);
}
// Casting a CGMutablePathRef to a CGPathRef seems to be the only way to convert what was just built into a UIBezierPath.
combinedGlyphsPath = [UIBezierPath bezierPathWithCGPath:(CGPathRef) combinedGlyphsPathRef];
CGPathRelease(combinedGlyphsPathRef);
}
return combinedGlyphsPath;
}
这是使用上述方法创建的旋转轮廓文本。也可以在文本层的 z 位置不明显的情况下添加透视。