光栅化
这里可能发生的是它决定必须将 textLayer 渲染为像素。请注意CALayer 类参考中的 shouldRasterize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。
所以，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doubleSided文本图层来防止这种情况。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，背面层旋转 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数量，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);
然后你会发现你可以在文字保持清晰的情况下将你的标志旋转到任何角度。
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，还有另一种方法：将文本转换为UIBezierPath表示形式。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，您可以为正在绘制的文本设置动画。
// - (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图。
