readRGB(3G)readRGB(3G)NAMEreadRGB - gets values of specific pixels
C SPECIFICATION
long readRGB(n, red, green, blue)
short n;
RGBvalue red[], green[], blue[];
PARAMETERS
n expects the number of pixels to be read by the function.
red expects the array in which the pixel red values will be stored.
green expects the array in which the pixel green values will be stored.
blue expects the array in which the pixel blue values will 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, namely, that
the starting point is not a valid character position.
DESCRIPTIONreadRGB attempts to read up to n pixel values from the bitplanes in RGB
mode. It reads them into the red, green, and blue arrays starting from
the current character position along a single scan line (constant y) in
the direction of increasing x. readRGB returns the number of pixels
read, which is the number requested if the starting point is a valid
character position (inside the current viewport). readRGB returns zero
if the starting point is not a valid character position. The values of
pixels read outside of the viewport or screen are undefined.
readRGB 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.
Pixels are read from the currently active framebuffer, as specified by
drawmode.
Thus, to read pixel values from the overlay bitplanes, for example,
simply set drawmode to OVERDRAW. Use readsource to specify the pixel
source within the current framebuffer (backbuffer, frontbuffer, or z-
buffer, for example) from which both rectread and lrectread take pixel
values.
In RGB double buffer mode, only the back buffer is read by default. On
machines that support it, you can use readsource to control which buffer
is read.
The system must be in RGB mode for readRGB to function correctly.
Page 1
readRGB(3G)readRGB(3G)SEE ALSO
lrectread, readsource, drawmode
NOTESreadRGB should not be used in new development. Rather, pixels should be
read using the high-performance lrectread command.
This routine is available only in immediate mode.
RGB pixels are written as 24-bit RGB triples. On systems with less than
the full bitplane configuration, the least significant bits of each R, G,
and B value are not used when pixels are read from the framebuffer. This
means that on 8-bit systems, the least significant 5 bits of each RGB
value are not used, and on 12 bitplane systems, the least significant 4
bits are set not used.
On IRIS-4D GT and GTX models, returned bits that do not correspond to
valid bitplanes are undefined. Other models return zero in these bits.
Page 2
