iOS - 使用OpenGL看起来效果不佳的文本

Question

我正在使用OpenGL ES 2.0绘制文本，但结果看起来不太好（尤其是“t”的底部）：

（它看起来有点像素化和模糊）

我不确切地知道为什么因为我以高分辨率（200px或400px）加载字体。

我在图像中绘制每个字符，组成纹理图集。所以所有的字符都可以随时显示而无需加载。我使用openGL（MVP矩阵）缩放纹理，但不管怎样它都不应该看起来那么差。

这是我用以下方法检索的char“t”的UIImage，在用openGL处理​​之前：

（没有OpenGL，你可以看到它看起来更好）

这是我用来从char创建图像的代码：

- (id)initWithString:(NSString *)string dimensions:(CGSize)dimensions alignment:(NSTextAlignment)alignment fontName:(NSString *)name fontSize:(CGFloat)size {
    NSUInteger width, height, i;
    CGContextRef context;
    void *data;
    CGColorSpaceRef colorSpace;
    UIFont *font;

    font = [UIFont fontWithName:name size:size];
    width = (NSUInteger)dimensions.width;
    height = (NSUInteger)dimensions.height;

    while(dimensions.width > kMaxTextureSize && size > 0) {
        font = [UIFont fontWithName:name size: --size];
        dimensions = [string sizeWithAttributes:@{NSFontAttributeName: font}];
        width = (GLuint)NextPowerOfTwo((int)dimensions.width);
        height = (GLuint)NextPowerOfTwo((int)dimensions.height);
    }

    colorSpace = CGColorSpaceCreateDeviceRGB();
    data = calloc(1, width * height * 4);

    context = CGBitmapContextCreate(data,
            width, height,
            8,
            4 * width,
            colorSpace,
            kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Big);

    CGColorSpaceRelease(colorSpace);

    CGContextSetRGBFillColor(context, 0.f, 0.f, 0.f, 1);
    CGContextTranslateCTM(context, 0.0, height);
    CGContextScaleCTM(context, 1.0f, -1.0f); //NOTE: NSString draws in UIKit referential i.e. renders upside-down compared to CGBitmapContext referential
    UIGraphicsPushContext(context);

    NSMutableParagraphStyle *style = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
    [style setLineBreakMode:NSLineBreakByWordWrapping];

    UIColor *whiteColor = [UIColor whiteColor];

    NSDictionary *attrsDictionary = @{
            NSFontAttributeName: font,
            NSBaselineOffsetAttributeName: @1.0F,
            NSParagraphStyleAttributeName: style,
            NSForegroundColorAttributeName: whiteColor
    };

    CGRect destRect = CGRectMake(0, 0, dimensions.width, dimensions.height);

    CGContextSetTextDrawingMode(context, kCGTextFill);
    CGContextSetAllowsAntialiasing(context, YES);
    CGContextSetShouldAntialias(context, YES);
    CGContextSetShouldSmoothFonts(context, YES);

    [string drawInRect:destRect
        withAttributes:attrsDictionary];

    CGImageRef cgImageFinal = CGBitmapContextCreateImage(context);

    UIGraphicsPopContext();

    self = [self initWithData:data pixelFormat:GL_RGBA
                   pixelsWide:width pixelsHigh:height];

    CGContextRelease(context);
    free(data);

    return self;
} 

这是从中检索openGL纹理的代码：

- (id)initWithData:(const void *)data
       pixelFormat:(GLenum)pixelFormat
        pixelsWide:(NSUInteger)width
        pixelsHigh:(NSUInteger)height {

    if ((self = [super init])) {
        glActiveTexture(GL_TEXTURE0);
        glGenTextures(1, &_texture);
        glBindTexture(GL_TEXTURE_2D, _texture);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

        switch (pixelFormat) {
            case GL_RGBA:
                glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
                break;
            case GL_RGB:
                glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, data);
                break;
            case GL_ALPHA:
                glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, data);
                break;
            default:
                [NSException raise:NSInternalInconsistencyException format:@""];
        }

        self.width = width;
        self.height = height;
    }
    return self;
} 

非常感谢任何帮助！