Andreas Pokorny wrote:
I just started using GIL, and I think I will need a mixture of packed thus interleaved pixels and a planar form: RGB565A8 The alpha channel is stored in a separate buffer. How can I discribe this pixel layout?
Here is a general strategy that will work with any type of format. If you look at the Mandelbrot function example, it takes a point defining the coordinates of the pixel within the image and returns a reference to the pixel. (The Mandelbrot view is immutable, so it returns the value of the pixel, but one can return a reference (proxy) for mutable views) You can use the Mandelbrot example as a starting point. In your function object you can keep a pointer to the source image (in your case, the two images, packed RGB and alpha) and replace the body of operator() to return the correct RGB565A8 reference. The GIL virtual view support takes care of everything you need to create an image view, and associated locators, x/y iterators, etc. The only thing you need to provide is the mapping from coordiantes to pixel reference. The disadvantage is that this could be suboptimal. It is often faster to compute the reference given a pointer to the pixel instead of given its coordinates. ________________ What I would do in your case is start from the interleaved_ptr example. This is an example of how to write pixel pointers and references. It creates the simplest possible models - that of an interleaved pixel pointer and reference. interleaved_ptr contains a pointer to the first channel of the current pixel and advances it accordingly. Upon dereferencing it returns an interlaved_ref - a model of a pixel reference, which also contains inside a pointer to the first channel of the current pixel. Its channel(), semantic_channel() and operator[] return references to the corresponding channels STEP 1: Create a model of a RGB565A8 pixel reference Start from interleaved_ref and extend it with a second pointer to the current alpha channel in the second image. But one complication in your case is that your pixel type is heterogeneous (meaning that not all of your channels have the same type). So you want to implement channel<0>() ... channel<3>() similar to the way they are implemented in packed3_pixel (which is an example of a model of a packed pixel reference). Your channel<4>() will simply dereference the alpha pointer. STEP 2: Create a model of a RGB565A8 pixel value You can use rgba8_pixel_t for the value type. Any class that is large enough to store the values of the channels will do. STEP 3: Create a model of a RGB565A8 pixel iterator Start from interleaved_ptr and extend it with a second pointer to the current alpha channel in the second image. Upon dereference it should construct your model of a pixel reference giving it the two pointers. You can now construct related types, such as a locator and a view, from your pixel iterator (see interleaved_ptr.cpp): typedef type_from_x_iterator<rgb565a8_ptr_t>::view_t rgb565a8_view_t; Lubomir