glDrawPixels man page on RedHat
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GLDRAWPIXELS(3G) OpenGL Manual GLDRAWPIXELS(3G)
NAME
glDrawPixels - write a block of pixels to the frame buffer
C SPECIFICATION
void glDrawPixels(GLsizei width, GLsizei height, GLenum format,
GLenum type, const GLvoid * data);
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_RGB,
GL_BGR, GL_RGBA, GL_BGRA, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA,
GL_LUMINANCE, and GL_LUMINANCE_ALPHA are accepted.
type
Specifies the data type for data. Symbolic constants
GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT,
GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2,
GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5,
GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1,
GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8,
GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, and
GL_UNSIGNED_INT_2_10_10_10_REV are accepted.
data
Specifies a pointer to the pixel data.
DESCRIPTION
glDrawPixels reads pixel data from memory and writes it into the frame
buffer relative to the current raster position, provided that the
raster position is valid. Use glRasterPos() or glWindowPos() to set the
current raster position; use glGet() with argument
GL_CURRENT_RASTER_POSITION_VALID to determine if the specified raster
position is valid, and glGet() 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:
glPixelStore(), glPixelTransfer(), glPixelMap(), and glPixelZoom().
This reference page describes the effects on glDrawPixels of many, but
not all, of the parameters specified by these four commands.
Data is read from data 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. When type is
one of GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT,
GL_UNSIGNED_INT, GL_INT, or GL_FLOAT each of these bytes, shorts,
integers, or floating-point values is interpreted as one color or depth
component, or one index, depending on format. When type is one of
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_SHORT_5_6_5,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_5_5_5_1,
GL_UNSIGNED_INT_8_8_8_8, or GL_UNSIGNED_INT_10_10_10_2, each unsigned
value is interpreted as containing all the components for a single
pixel, with the color components arranged according to format. When
type is one of GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8_REV, or GL_UNSIGNED_INT_2_10_10_10_REV, each
unsigned value is interpreted as containing all color components,
specified by format, for a single pixel in a reversed order. 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 glPixelStore()).
width × height pixels are read from memory, starting at location data.
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 glPixelStore() 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
glPixelStore() reference page for details on these options.
If a non-zero named buffer object is bound to the
GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer()) while a block of
pixels is specified, data is treated as a byte offset into the buffer
object's data store.
The width × height pixels that are read from memory are each operated
on in the same way, based on the values of several parameters specified
by glPixelTransfer() and glPixelMap(). 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 13 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 2 b - 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 n = x r + n % width y n
= y r + n width .sp where x r y r 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_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 2 b - 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 n = x r + n % width y n = y r + n width
where x r y r 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
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 n = x r + n % width y n = y r + n width
where x r y r 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
GL_BGRA
Each pixel is a four-component group: For GL_RGBA, the red
component is first, followed by green, followed by blue, followed
by alpha; for GL_BGRA the order is blue, green, red and then 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 n = x r + n % width y n = y r + n width
where x r y r 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
GL_BGR
Each pixel is a three-component group: red first, followed by
green, followed by blue; for GL_BGR, the first component is blue,
followed by green and then red. 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 │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_BYTE_3_3_2 │ unsigned 8-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_BYTE_2_3_3_REV │ unsigned 8-bit integer with reversed component │
│ │ ordering │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_5_6_5 │ unsigned 16-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_5_6_5_REV │ unsigned 16-bit integer with reversed component │
│ │ ordering │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_4_4_4_4 │ unsigned 16-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_4_4_4_4_REV │ unsigned 16-bit integer with reversed component │
│ │ ordering │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_5_5_5_1 │ unsigned 16-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_SHORT_1_5_5_5_REV │ unsigned 16-bit integer with reversed component │
│ │ ordering │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_INT_8_8_8_8 │ unsigned 32-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_INT_8_8_8_8_REV │ unsigned 32-bit integer with reversed component │
│ │ ordering │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_INT_10_10_10_2 │ unsigned 32-bit integer │
├─────────────────────────────────────────────┼───────────────────────────────────────────────────────┤
│GL_UNSIGNED_INT_2_10_10_10_REV │ unsigned 32-bit integer with reversed component │
│ │ ordering │
└─────────────────────────────────────────────┴───────────────────────────────────────────────────────┘
The rasterization described so far assumes pixel zoom factors of 1. If
glPixelZoom() is used to change the x and y pixel zoom factors, pixels
are converted to fragments as follows. If x r y r is the current raster
position, and a given pixel is in 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 r + zoom x n y r + zoom y m
where zoom x is the value of GL_ZOOM_X and zoom y is the value of
GL_ZOOM_Y.
NOTES
GL_BGR and GL_BGRA are only valid for format if the GL version is 1.2
or greater.
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, and GL_UNSIGNED_INT_2_10_10_10_REV are only
valid for type if the GL version is 1.2 or greater.
ERRORS
GL_INVALID_ENUM is generated if format or type is not one of the
accepted values.
GL_INVALID_ENUM is generated if type is GL_BITMAP and format is not
either GL_COLOR_INDEX or GL_STENCIL_INDEX.
GL_INVALID_VALUE is generated if either width or height is negative.
GL_INVALID_OPERATION is generated if format is GL_STENCIL_INDEX and
there is no stencil buffer.
GL_INVALID_OPERATION is generated if format is GL_RED, GL_GREEN,
GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_BGR, GL_BGRA, GL_LUMINANCE, or
GL_LUMINANCE_ALPHA, and the GL is in color index mode.
GL_INVALID_OPERATION is generated if format is one of
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, or GL_UNSIGNED_SHORT_5_6_5_REV and format is
not GL_RGB.
GL_INVALID_OPERATION is generated if format is one of
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV and
format is neither GL_RGBA nor GL_BGRA.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is
bound to the GL_PIXEL_UNPACK_BUFFER target and the buffer object's data
store is currently mapped.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is
bound to the GL_PIXEL_UNPACK_BUFFER target and the data would be
unpacked from the buffer object such that the memory reads required
would exceed the data store size.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is
bound to the GL_PIXEL_UNPACK_BUFFER target and data is not evenly
divisible into the number of bytes needed to store in memory a datum
indicated by type.
GL_INVALID_OPERATION is generated if glDrawPixels is executed between
the execution of glBegin() and the corresponding execution of glEnd().
ASSOCIATED GETS
glGet() with argument GL_CURRENT_RASTER_POSITION
glGet() with argument GL_CURRENT_RASTER_POSITION_VALID
glGet() with argument GL_PIXEL_UNPACK_BUFFER_BINDING
SEE ALSO
glAlphaFunc(), glBlendFunc(), glCopyPixels(), glDepthFunc(),
glLogicOp(), glPixelMap(), glPixelStore(), glPixelTransfer(),
glPixelZoom(), glRasterPos(), glReadPixels(), glScissor(),
glStencilFunc(), glWindowPos()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLDRAWPIXELS(3G)
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