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This file describes possible customizations of the libxmi library. Please
read the file README first; it describes what libxmi does.
1. If desired, modify the default definition of `miPixel' in ./xmi.h by
defining the MI_PIXEL_TYPE preprocessor symbol at compile time. Each
point in a miPaintedSet is painted with a miPixel, but what a miPixel
is, is up to you. By default it is an `unsigned int', but it could be
another integer type, a floating point type, a structure, a union...
That would be arranged by defining MI_PIXEL_TYPE. If MI_PIXEL_TYPE is a
structure or a union, the macro MI_SAME_PIXEL(), which tests two
miPixels for equality, should be redefined too.
2. If desired, define the macro MI_DEFAULT_MERGE2_PIXEL() also. As
explained in ./xmi.h, by default, miCopyPaintedSetToCanvas() uses the
Painter's Algorithm (a source pixel replaces a destination pixel). That
may be altered programatically by invoking miSetPixelMerge2(). But at
installation time, the default behavior may be altered too, by defining
the macro MI_DEFAULT_MERGE2_PIXEL(new, source, dest). For example, if
the miPixel datatype is defined to include an alpha component as well as
color components, a change would be called for.
3. The same, for the macro MI_DEFAULT_MERGE3_PIXEL(). This macro is used
when a "texture" pixel is available as part of a miCanvas, and must be
taken into account, besides the source pixel and the destination pixel
already on the miCanvas.
4. If desired, customize the definition of the `drawable' contained within
an miCanvas by defining the symbol MI_CANVAS_DRAWABLE_TYPE. If this is
not defined, the drawable will be an miPixmap. If you define
MI_CANVAS_DRAWABLE_TYPE, you will also need to define the accessor
macros MI_GET_CANVAS_DRAWABLE_PIXEL(pCanvas, x, y, pixel) and
MI_SET_CANVAS_DRAWABLE_PIXEL(pCanvas, x, y, pixel). The macro
MI_GET_CANVAS_DRAWABLE_BOUNDS(pCanvas, xleft, ytop, xright, ybottom)
should be defined too. See ./xmi.h.
Actually, if you are interested only in the first stage of the graphics
pipeline, i.e., the painting of pixels in a miPaintedSet by the eight
drawing functions in the core API, only modification #1 above is relevant.
A miPaintedSet is an opaque object, but by looking at the function
miCopyPaintedSetToCanvas() in the file mi_canvas.c, you should be able to
see how it is laid out. It would be trivial to write your own function
that copies pixels out of a miPaintedSet, i.e., to rewrite the second stage
of the graphics pipeline from scratch in a completely customized way.
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