Images and Image Views

Images, formats, views and pixels. More...

Classes
class	Argb32Image
	ARGB-32 image. More...
class	Rgb32Image
	Premultiplied ARGB-32 image. More...
class	Argb32Pixel
	Cursor to one ARGB-32 pixel. More...
class	Argb32ConstPixel
	Read-only cursor to one ARGB-32 pixel. More...
class	Argb32
	ARGB-32 image format. More...
class	Color
	8-bit ARGB color. More...
class	ColorF
	Floating-point RGBA color. More...
class	BasicImage< FormatT, TraitsT >
	Image that owns or wraps pixel data. More...
class	BasicConstImage< FormatT, TraitsT >
	Read-only wrap of pixel data. More...
class	ImageFormat
	Runtime pixel format. More...
class	Pixel< ColorT >
	Cursor to one pixel. More...
class	ConstPixel< ColorT >
	Read-only cursor to one pixel. More...
class	JpegReader
	JPEG image reader. More...
class	PngReader
	PNG image reader. More...
class	PngWriter
	PNG image writer. More...
class	BasicView< FormatT, TraitsT >
	Non-owning image region. More...
class	BasicConstView< FormatT, TraitsT >
	Read-only image region. More...
class	ViewBase
	Width, height and stride of an image or view. More...

Detailed Description

An image is a rectangular pixel buffer. BasicImage either owns that buffer or wraps a caller-supplied one. Constructors that take width and height allocate. Constructors that take a data pointer wrap; the buffer must cover the given size and padding and must remain valid for the lifetime of the image. reset() switches between those two modes. clear() drops the buffer. Copying an owning image copies the pixels. A wrapped image does not take ownership on copy of the pointer; the original buffer still belongs to the caller.

Format is either a compile-time type or a runtime value. A typed image binds the format in the template argument: Argb32Image, Rgb32Image, Rgb16Image, and Yuv12Image are BasicImage specializations, and their pixels are the matching concrete types such as Argb32Pixel. Use a typed image when the calling code already knows the format. Image selects the format at runtime through ImageFormat. Decoders, file loaders, and other input that discovers a format while running use Image. Image exposes Pixel<Color>. ImageF is not a float storage format: it is a ColorF lens on the same runtime ImageFormat, and it exposes Pixel<ColorF>. The generic pixels forward storage operations to the selected format.

Color is the 8-bit working color, stored as a packed ARGB value with straight alpha. ColorF is a four-float working color in RGBA order, with channels in the unit interval and values above 1 allowed for HDR. Neither type is a pixel buffer. Pixels convert to and from the working color of their traits.

Views do not copy pixels. The free functions view(), pixelView(), and lineView() build a non-owning region, a pixel-iterator range, or a row span over an image or another view. Each view keeps the source format, typed or runtime, and the source buffer must outlive the view. ViewBase stores width, height, and stride for every image and view.

A pixel object is a cursor, not a color value. It refers to one position in an image or view. Copy construction duplicates the cursor. Copy assignment is deleted so a pixel = other cannot silently rebind the position; call reset() to bind another location. Assigning a Color or calling assign() writes through to storage. advance() and skipPadding() walk the buffer in scanline order.

JPEG and PNG codecs read and write Image values on iostreams. JpegReader and PngReader attach a stream and an image, then get() fills that image. PngWriter attaches an output stream and write() emits the image. The reader owns neither the stream nor the image.

Add a format by deriving it from ImageFormat, implementing its pixel storage operations, and providing the matching concrete pixel types and an ImageTraits specialization. Typed images then use the format as a BasicImage argument, and the runtime image API uses it through ImageFormat.

The example decodes a JPEG into a runtime Image and opens a crop that does not copy pixels.

std::ifstream in("photo.jpg", std::ios::binary);
Pt::Gfx::Image image;
Pt::Gfx::JpegReader reader(in, image);
reader.get();
 
Pt::Gfx::ImageView crop = Pt::Gfx::view(image, 10, 10, 64, 64);