readpi(3G)readpi(3G)NAMEreadpi - returns values of specific pixels
FORTRAN SPECIFICATION
integer*4 function readpi(n, colors)
integer*4 n
integer*2 colors(n)PARAMETERS
n expects the number of pixels to be read by the function.
colors expects the array in which the pixel values are to be stored.
FUNCTION RETURN VALUE
The returned value of this function is the number of pixels actually
read. A returned function value of 0 indicates an error, that the
starting point is not a valid character position.
DESCRIPTIONreadpi attempts to read up to n pixel values from the bitplanes in color
map mode. It reads them into the array colors starting from the current
character position along a single scan line (constant y) in the direction
of increasing x. readpi returns the number of pixels read, which is the
number requested if the starting point is a valid character position
(inside the current viewport). readpi returns zero if the starting point
is not a valid character position. The values of pixels read outside the
viewport or the screen are undefined. readpi updates the current
character position to one pixel to the right of the last one read; the
current character position is undefined if the new position is outside
the viewport.
In double buffer mode, only the back buffer is read by default. On
machines that support it, you can use readso to control which buffer is
read.
The system must be in color map mode for readpi to function correctly.
SEE ALSO
lrectr, readso
NOTESreadpi should not be used in new development. Rather, pixels should be
read using the high-performance lrectr command.
This routine is available only in immediate mode.
The upper bits of a color value (an element of the colors array) are
undefined. You can write this information to the frame buffer without
problems. However, if you intend to interpret this data, be sure you
mask out the upper bits.
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readpi(3G)readpi(3G)BUGS
On IRIS-4D GT and GTX models, when reading pixels from the PUPMODE
planes, the returned bits are shifted up by two bits.
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