glDrawPixels

a b c d e f g h i j k l m n o p q r s t u v w x y z _

GLDRAWPIXELS(3G) 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 *pixels )

PARAMETERS
width, height Specify the dimensions of the pixel rectangle to be
written into the frame buffer.

format Specifies the 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 pixels. 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.

pixels 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 to set the current raster position; use glGet with argu-
ment 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 ref-
erence page describes the effects on glDrawPixels 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-pre-
cision 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, 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,
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 pix-
els, with bit ordering determined by GL_UNPACK_LSB_FIRST (see
glPixelStore).

width×height 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 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.

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 spe-
cific to the 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 con-
verted to fixed-point , 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 loca-
tions 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 coordi-
nate and texture coordinates to each pixel, then assigning x
and y window coordinates to the nth fragment such that

xn=xr+nmodwidth

yn=yr+⌊n/width⌋

where (xr,yr) 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 con-
verted to fixed-point , 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 loca-
tions in the result. If GL_MAP_STENCIL is true, the index
is replaced with the value that it references in lookup ta-
ble 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

xn=xr+nmodwidth

yn=yr+⌊n/width⌋

where (xr,yr) 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
with unspecified precision. Signed integer data is mapped
linearly to the internal floating-point
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 frag-
ments 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

xn=xr+nmodwidth

yn=yr+⌊n/width⌋

where (xr,yr) 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 frag-
ments are written to the frame buffer.

GL_RGBA

GL_BGRA
Each pixel is a four-component group: for GL_RGBA, the red com-
ponent 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
with unspecified precision. Signed integer values are mapped
linearly to the internal floating-point
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 coor-
dinates to the nth fragment such that

xn=xr+nmodwidth

yn=yr+⌊n/width⌋

where (xr,yr) 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 frag-
ments are written to the frame buffer.

GL_RED Each pixel is a single red component. This component is con-
verted to the internal floating-point 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 con-
verted to the internal floating-point 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 con-
verted to the internal floating-point 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 con-
verted to the internal floating-point 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 con-
verted to the internal floating-point 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 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 lumi-
nance 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 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 (xr, yr) 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

(xr+zoomxn, yr+zoomym)

(xr+zoomx(n+1), yr+zoomy(m+1))

where zoomx is the value of GL_ZOOM_X and zoomy 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_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_BGR, GL_BGRA, 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 glDrawPixels is executed between
the execution of glBegin and the corresponding execution of glEnd.

GL_INVALID_OPERATION is generated if format is one
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, of 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 for-
mat is neither GL_RGBA nor GL_BGRA.

ASSOCIATED GETS
glGet with argument GL_CURRENT_RASTER_POSITION
glGet with argument GL_CURRENT_RASTER_POSITION_VALID

SEE ALSO
glAlphaFunc(3G), glBlendFunc(3G), glCopyPixels(3G), glDepthFunc(3G),
glLogicOp(3G), glPixelMap(3G), glPixelStore(3G), glPixelTransfer(3G),
glPixelZoom(3G), glRasterPos(3G), glReadPixels(3G), glScissor(3G),
glStencilFunc(3G)

GLDRAWPIXELS(3G)