C SPECIFICATION
void GLAPIENTRY glDrawPixels( GLsizei width,
GLsizei heigh )
PARAMETERS
width, heigh Specify the dimensions of the pixel rectangle to be writ-
ten into the frame buffer.
_param3 Specifies the format of the pixel data. Symbolic con-
stants 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.
_param4 Specifies the data type for _param5. 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.
_param5 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 posi-
tion is valid. Use
glRasterPos 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 con-
trol 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 _param5 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 _param4. When _param4 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, inte-
gers, or floating-point values is interpreted as one color or depth
ponents are referred to as pixels. If _param4 is GL_BITMAP, the data
must be unsigned bytes, and _param3 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).
widthxheigh pixels are read from memory, starting at location _param5.
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 param-
eters 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 widthxheigh 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 _param3. _param3 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 val-
ues. 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 neg-
ative, 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 coordi-
nate and texture coordinates to each pixel, then assigning x
and y window coordinates to the nth fragment such that
bits to the right of the binary point, regardless of the mem-
ory 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
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 format with
unspecified precision. Signed integer data is mapped linearly
to the internal floating-point format such that the most posi-
tive representable integer value maps to 1.0, and the most nega-
tive 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
xn=xr+nmodwidth
yn=yr+?n/width?
where (xr,yr) is the current raster position. These pixel frag-
ments are then treated just like the fragments generated by ras-
terizing points, lines, or polygons. Texture mapping, fog, and
maps to -1.0. (Note that this mapping does not convert 0 pre-
cisely 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 coordi-
nates to the nth fragment such that
xn=xr+nmodwidth
yn=yr+?n/width?
where (xr,yr) is the current raster position. These pixel frag-
ments are then treated just like the fragments generated by ras-
terizing 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 con-
verted 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 con-
verted 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 con-
verted 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.
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
------------------------------------------------------------------------------------------
GL_ZOOM_Y.
NOTES
GL_BGR and GL_BGRA are only valid for _param3 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 _param4 if the GL version is 1.2 or greater.
ERRORS
GL_INVALID_VALUE is generated if either width or heigh is negative.
GL_INVALID_ENUM is generated if _param3 or _param4 is not one of the
accepted values.
GL_INVALID_OPERATION is generated if _param3 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 _param4 is GL_BITMAP and _param3 is not
either GL_COLOR_INDEX or GL_STENCIL_INDEX.
GL_INVALID_OPERATION is generated if _param3 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 _param3 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 _param3 is
not GL_RGB.
GL_INVALID_OPERATION is generated if _param3 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
_param3 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, glBlendFunc, glCopyPixels, glDepthFunc, glLogicOp,
glPixelMap, glPixelStore, glPixelTransfer, glPixelZoom, glRasterPos,
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