NAME
fglDrawPixels - write a block of pixels to the frame buffer
FORTRAN SPECIFICATION
SUBROUTINE fglDrawPixels( INTEGER*4 width,
INTEGER*4 height,
INTEGER*4 format,
INTEGER*4 type,
CHARACTER*8 pixels )
PARAMETERS
width, height Specify the dimensions of the pixel rectangle
to be written into the frame buffer.
format Specifies the format of the pixel data.
Symbolic constants GL_COLOR_INDEX,
GL_STENCIL_INDEX, GL_DEPTH_COMPONENT, GL_RGBA,
GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB,
GL_LUMINANCE, and GL_LUMINANCE_ALPHA are
accepted.
type Specifies the data type for pixels. Symbolic
constants GL_UNSIGNED_BYTE, GL_BYTE,
GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT,
GL_UNSIGNED_INT, GL_INT, and GL_FLOAT are
accepted.
pixels Specifies a pointer to the pixel data.
DESCRIPTION
fglDrawPixels reads pixel data from memory and writes it
into the frame buffer relative to the current raster
position. Use fglRasterPos to set the current raster
position; use fglGet with argument
GL_CURRENT_RASTER_POSITION to query the raster position.
Several parameters define the encoding of pixel data in
memory and control the processing of the pixel data before
it is placed in the frame buffer. These parameters are set
with four commands: fglPixelStore, fglPixelTransfer,
fglPixelMap, and fglPixelZoom. This reference page
describes the effects on fglDrawPixels of many, but not all,
of the parameters specified by these four commands.
Data is read from pixels as a sequence of signed or unsigned
bytes, signed or unsigned shorts, signed or unsigned
integers, or single-precision floating-point values,
depending on type. Each of these bytes, shorts, integers,
or floating-point values is interpreted as one color or
depth component, or one index, depending on format. Indices
are always treated individually. Color components are
treated as groups of one, two, three, or four values, again
based on format. Both individual indices and groups of
components are referred to as pixels. If type is GL_BITMAP,
the data must be unsigned bytes, and format must be either
GL_COLOR_INDEX or GL_STENCIL_INDEX. Each unsigned byte is
treated as eight 1-bit pixels, with bit ordering determined
by GL_UNPACK_LSB_FIRST (see fglPixelStore).
widthxheight pixels are read from memory, starting at
location pixels. By default, these pixels are taken from
adjacent memory locations, except that after all width
pixels are read, the read pointer is advanced to the next
four-byte boundary. The four-byte row alignment is
specified by fglPixelStore with argument
GL_UNPACK_ALIGNMENT, and it can be set to one, two, four, or
eight bytes. Other pixel store parameters specify different
read pointer advancements, both before the first pixel is
read and after all width pixels are read. See the
fglPixelStore reference page for details on these options.
The widthxheight pixels that are read from memory are each
operated on in the same way, based on the values of several
parameters specified by fglPixelTransfer and fglPixelMap.
The details of these operations, as well as the target
buffer into which the pixels are drawn, are specific to the
format of the pixels, as specified by format. format can
assume one of eleven symbolic values:
GL_COLOR_INDEX
Each pixel is a single value, a color index. It
is converted to fixed-point format, with an
unspecified number of bits to the right of the
binary point, regardless of the memory data type.
Floating-point values convert to true fixed-point
values. Signed and unsigned integer data is
converted with all fraction bits set to 0. Bitmap
data convert to either 0 or 1.
Each fixed-point index is then shifted left by
GL_INDEX_SHIFT bits and added to GL_INDEX_OFFSET.
If GL_INDEX_SHIFT is negative, the shift is to the
right. In either case, zero bits fill otherwise
unspecified bit locations in the result.
If the GL is in RGBA mode, the resulting index is
converted to an RGBA pixel with the help of the
GL_PIXEL_MAP_I_TO_R, GL_PIXEL_MAP_I_TO_G,
GL_PIXEL_MAP_I_TO_B, and GL_PIXEL_MAP_I_TO_A
tables. If the GL is in color index mode, and if
GL_MAP_COLOR is true, the index is replaced with
the value that it references in lookup table
GL_PIXEL_MAP_I_TO_I. Whether the lookup
replacement of the index is done or not, the
integer part of the index is then ANDed with 2b-1,
where b is the number of bits in a color index
buffer.
The GL then converts the resulting indices or RGBA
colors to fragments by attaching the current
raster position z coordinate and texture
coordinates to each pixel, then assigning x and y
window coordinates to the nth fragment such that
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position.
These pixelrfragments are then treated just like
the fragments generated by rasterizing points,
lines, or polygons. Texture mapping, fog, and all
the fragment operations are applied before the
fragments are written to the frame buffer.
GL_STENCIL_INDEX
Each pixel is a single value, a stencil index. It
is converted to fixed-point format, with an
unspecified number of bits to the right of the
binary point, regardless of the memory data type.
Floating-point values convert to true fixed-point
values. Signed and unsigned integer data is
converted with all fraction bits set to 0. Bitmap
data convert to either 0 or 1.
Each fixed-point index is then shifted left by
GL_INDEX_SHIFT bits, and added to GL_INDEX_OFFSET.
If GL_INDEX_SHIFT is negative, the shift is to the
right. In either case, zero bits fill otherwise
unspecified bit locations in the result. If
GL_MAP_STENCIL is true, the index is replaced with
the value that it references in lookup table
GL_PIXEL_MAP_S_TO_S. Whether the lookup
replacement of the index is done or not, the
integer part of the index is then ANDed with 2b-1,
where b is the number of bits in the stencil
buffer. The resulting stencil indices are then
written to the stencil buffer such that the nth
index is written to location
x = x + n mod width
n r
y = y + | n/width |
where (x ,y ) is the current raster position. Only the
pixel ownership test, the scissor test, and the stencil
writemask affect these write operations.
GL_DEPTH_COMPONENT
Each pixel is a single-depth component. Floating-point
data is converted directly to an internal floating-
point format with unspecified precision. Signed
integer data is mapped linearly to the internal
floating-point format such that the most positive
representable integer value maps to 1.0, and the most
negative representable value maps to -1.0. Unsigned
integer data is mapped similarly: the largest integer
value maps to 1.0, and 0 maps to 0.0. The resulting
floating-point depth value is then multiplied by by
GL_DEPTH_SCALE and added to GL_DEPTH_BIAS. The result
is clamped to the range [0,1].
The GL then converts the resulting depth components to
fragments by attaching the current raster position
color or color index and texture coordinates to each
pixel, then assigning x and y window coordinates to the
nth fragment such that
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position. These
pixel fragments are then treated just like the
fragments generated by rasterizing points, lines, or
polygons. Texture mapping, fog, and all the fragment
operations are applied before the fragments are written
to the frame buffer.
GL_RGBA
Each pixel is a four-component group: for GL_RGBA, the
red component is first, followed by green, followed by
blue, followed by alpha. Floating-point values are
converted directly to an internal floating-point format
with unspecified precision. Signed integer values are
mapped linearly to the internal floating-point format
such that the most positive representable integer value
maps to 1.0, and the most negative representable value
maps to -1.0. (Note that this mapping does not convert
0 precisely to 0.0.) Unsigned integer data is mapped
similarly: the largest integer value maps to 1.0, and
0 maps to 0.0. The resulting floating-point color
values are then multiplied by GL_c_SCALE and added to
GL_c_BIAS, where c is RED, GREEN, BLUE, and ALPHA for
the respective color components. The results are
clamped to the range [0,1].
If GL_MAP_COLOR is true, each color component is scaled
by the size of lookup table GL_PIXEL_MAP_c_TO_c, then
replaced by the value that it references in that table.
c is R, G, B, or A respectively.
The GL then converts the resulting RGBA colors to
fragments by attaching the current raster position z
coordinate and texture coordinates to each pixel, then
assigning x and y window coordinates to the nth
fragment such that
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position. These
pixel fragments are then treated just like the
fragments generated by rasterizing points, lines, or
polygons. Texture mapping, fog, and all the fragment
operations are applied before the fragments are written
to the frame buffer.
GL_RED
Each pixel is a single red component. This component
is converted to the internal floating-point format in
the same way the red component of an RGBA pixel is. It
is then converted to an RGBA pixel with green and blue
set to 0, and alpha set to 1. After this conversion,
the pixel is treated as if it had been read as an RGBA
pixel.
GL_GREEN
Each pixel is a single green component. This component
is converted to the internal floating-point format in
the same way the green component of an RGBA pixel is.
It is then converted to an RGBA pixel with red and blue
set to 0, and alpha set to 1. After this conversion,
the pixel is treated as if it had been read as an RGBA
pixel.
GL_BLUE
Each pixel is a single blue component. This component
is converted to the internal floating-point format in
the same way the blue component of an RGBA pixel is.
It is then converted to an RGBA pixel with red and
green set to 0, and alpha set to 1. After this
conversion, the pixel is treated as if it had been read
as an RGBA pixel.
GL_ALPHA
Each pixel is a single alpha component. This component
is converted to the internal floating-point format in
the same way the alpha component of an RGBA pixel is.
It is then converted to an RGBA pixel with red, green,
and blue set to 0. After this conversion, the pixel is
treated as if it had been read as an RGBA pixel.
GL_RGB
Each pixel is a three-component group: red first,
followed by green, followed by blue. Each component is
converted to the internal floating-point format in the
same way the red, green, and blue components of an RGBA
pixel are. The color triple is converted to an RGBA
pixel with alpha set to 1. After this conversion, the
pixel is treated as if it had been read as an RGBA
pixel.
GL_LUMINANCE
Each pixel is a single luminance component. This
component is converted to the internal floating-point
format in the same way the red component of an RGBA
pixel is. It is then converted to an RGBA pixel with
red, green, and blue set to the converted luminance
value, and alpha set to 1. After this conversion, the
pixel is treated as if it had been read as an RGBA
pixel.
GL_LUMINANCE_ALPHA
Each pixel is a two-component group: luminance first,
followed by alpha. The two components are converted to
the internal floating-point format in the same way the
red component of an RGBA pixel is. They are then
converted to an RGBA pixel with red, green, and blue
set to the converted luminance value, and alpha set to
the converted alpha value. After this conversion, the
pixel is treated as if it had been read as an RGBA
pixel.
The following table summarizes the meaning of the valid
constants for the type parameter:
____________________________________________________________
| type | corresponding type |
|__________________|________________________________________|
|GL_UNSIGNED_BYTE | unsigned 8-bit integer |
| GL_BYTE | signed 8-bit integer |
| GL_BITMAP | single bits in unsigned 8-bit integers |
|GL_UNSIGNED_SHORT | unsigned 16-bit integer |
| GL_SHORT | signed 16-bit integer |
| GL_UNSIGNED_INT | unsigned 32-bit integer |
| GL_INT | 32-bit integer |
| GL_FLOAT | single-precision floating-point |
|__________________|________________________________________|
The rasterization described so far assumes pixel zoom
factors of 1. If
fglPixelZoom is used to change the x and y pixel zoom
factors, pixels are converted to fragments as follows. If
(x , y ) is the current raster position, and a given pixel
isrin the nth column and mth row of the pixel rectangle,
then fragments are generated for pixels whose centers are in
the rectangle with corners at
(x +zoom n, y +zoom m)
r x r y
(x +zoom (n+1), y +zoom (m+1))
r x r y
where zoom is the value of GL_ZOOM_X and zoom is the value
of GL_ZOOM_Y. y
ERRORS
GL_INVALID_VALUE is generated if either width or height is
negative.
GL_INVALID_ENUM is generated if format or type is not one of
the accepted values.
GL_INVALID_OPERATION is generated if format is GL_RED,
GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE,
or GL_LUMINANCE_ALPHA, and the GL is in color index mode.
GL_INVALID_ENUM is generated if type is GL_BITMAP and format
is not either GL_COLOR_INDEX or GL_STENCIL_INDEX.
GL_INVALID_OPERATION is generated if format is
GL_STENCIL_INDEX and there is no stencil buffer.
GL_INVALID_OPERATION is generated if fglDrawPixels is
executed between the execution of fglBegin and the
corresponding execution of fglEnd.
ASSOCIATED GETS
fglGet with argument GL_CURRENT_RASTER_POSITION
fglGet with argument GL_CURRENT_RASTER_POSITION_VALID
SEE ALSO
fglAlphaFunc, fglBlendFunc, fglCopyPixels, fglDepthFunc,
fglLogicOp, fglPixelMap, fglPixelStore, fglPixelTransfer,
fglPixelZoom, fglRasterPos, fglReadPixels, fglScissor,
fglStencilFunc