NAME
vpSetImage - specify an image array
SYNOPSIS
#include <volpack.h>
vpResult
vpSetImage(vpc, image, width, height, scan_bytes, pixel_type)
vpContext *vpc;
unsigned char *image;
int width, height;
int scan_bytes;
int pixel_type;
ARGUMENTS
vpc VolPack context from vpCreateContext.
image 2D array for storing result images.
width Width of image in pixels.
height Height of image in pixels.
scan_bytes
Number of bytes per scanline in image array.
pixel_type
Code indicating the format of each pixel in the array.
DESCRIPTION
vpSetImage is used to specify a buffer for storing the result image
during rendering. The width and height parameters specify the size of
the result image. The clipping window (see vpWindow(3) or
vpWindowPHIGS(3)) is scaled to exactly match the specified size. The
scan_bytes argument specifies the size of a scanline in the image
array, in bytes. This argument can be used to add padding to the end
of each scanline to satisfy alignment restrictions (e.g. raster
operations sometimes require the beginning of each scanline to lie on a
word boundary). The pixel_type argument specifies the format of a
pixel. The following formats are supported:
VP_ALPHA
Each pixel is one byte and contains an 8-bit alpha channel
(containing an opacity or coverage value for the pixel).
VP_LUMINANCE
Each pixel is one byte and contains an 8-bit grayscale
intensity.
VP_LUMINANCEA
Each pixel is two bytes and contains an 8-bit grayscale
intensity followed by an 8-bit alpha channel.
VP_RGB Each pixel is three bytes and contains an RGB color (8
bits/channel). The R channel is stored first, followed by G and
then B.
VP_RGBA
Each pixel is four bytes and contains an RGBA color with an
alpha channel (8 bits/channel). The R channel is stored first,
followed by G, B and A.
VP_BGR Each pixel is three bytes and contains an RGB color (8
bits/channel). The B channel is stored first, follow by G and
then R.
VP_ABGR
Each pixel is four bytes and contains an RGBA color with an
alpha channel (8 bits/channel). The A channel is stored first,
followed by B, G and R.
The formats VP_LUMINANCE and VP_LUMINANCEA may only be used with
grayscale shaders (the color_channels argument to vpSetLookupShader
must be 1, or if you are using a callback function for shading you must
use the VP_GRAY_SHADE_FUNC argument to vpSetCallback). The formats
VP_RGB, VP_RGBA, VP_BGR and VP_ABGR may only be used with color
shaders. The format VP_ALPHA may be used with either type of shader.
The size of the image array must be:
unsigned char image[height][scan_bytes];
The scan_bytes argument must be at least width times the number of
bytes per pixel. Pixels in a horizontal scanline are packed next to
each other, regardless of the size of the pixel. Any extra padding
bytes at the end of a scanline are not modified.
The alpha channel may be used to composite the rendered image against a
background image. Alpha gives the fraction of the background that is
visible through the rendered image (0 for fully visible, 255 for fully
obscured). As an example, to change the background color of the image
to a solid color C, modify the color of each pixel in the image
according to the formula:
color(x,y) += C * (1 - alpha(x,y)/255)
STATE VARIABLES
The current image array properties can be retrieved with the following
state variable codes (see vpGeti(3)): VP_IMAGE, VP_IMAGE_WIDTH,
VP_IMAGE_HEIGHT, VP_IMAGE_SCAN_SIZE, VP_PIXEL_TYPE.
ERRORS
The return value is always VP_OK.
SEE ALSO
VolPack(3), vpCreateContext(3), vpRenderRawVolume(3)