Pixmaps represent a set of pixels for a 2 dimensional region of a plane. Each pixel has n components per pixel. The components are in the order process-components, spot-colors, alpha, where there can be 0 of any of those types. The data is in premultiplied alpha when rendering, but non-premultiplied for colorspace conversions and rescaling.
x, y: The minimum x and y coord of the region in pixels.
w, h: The width and height of the region in pixels.
n: The number of color components in the image. n = num composite colors + num spots + num alphas
s: The number of spot channels in the image.
alpha: 0 for no alpha, 1 for alpha present.
flags: flag bits. Bit 0: If set, draw the image with linear interpolation. Bit 1: If set, free the samples buffer when the pixmap is destroyed.
stride: The byte offset from the data for any given pixel to the data for the same pixel on the row below.
seps: NULL, or a pointer to a separations structure. If NULL, s should be 0.
xres, yres: Image resolution in dpi. Default is 96 dpi.
colorspace: Pointer to a colorspace object describing the colorspace the pixmap is in. If NULL, the image is a mask.
samples: Pointer to the first byte of the pixmap sample data. This is typically a simple block of memory w * h * n bytes of memory in which the components are stored linearly, but with the use of appropriate stride values, scanlines can be stored in different orders, and have different amounts of padding. The first n bytes are components 0 to n-1 for the pixel at (x,y). Each successive n bytes gives another pixel in scanline order as we move across the line. The start of each scanline is offset the start of the previous one by stride bytes.
