GLsizei heigh )
PARAMETERS
width, heigh Specify the dimensions of the pixel rectangle to be written
into the frame buffer.
_param3 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.
_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 de‐
scribes the effects on glDrawPixels of many, but not all, of the parame‐
ters 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-preci‐
sion 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 com‐
ponent, or one index, depending on _param3. When _param4 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
width×heigh pixels are read from memory, starting at location _param5.
By default, these pixels are taken from adjacent memory locations, ex‐
cept that after all width pixels are read, the read pointer is advanced
to the next four-byte boundary. The four-byte row alignment is speci‐
fied 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 ref‐
erence page for details on these options.
The width×heigh 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 as‐
sume 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 nega‐
tive, 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
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
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
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 af‐
fect 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 un‐
specified 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 re‐
sult 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
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 compo‐
nent is first, followed by green, followed by blue, followed by
alpha; for GL_BGRA the order is blue, green, red and then alpha.
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 re‐
spectively.
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. Af‐
ter 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. Af‐
ter 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 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 con‐
version, the pixel is treated as if it had been read as an RGBA
pixel.
GL_RGB
minance 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 float‐
ing-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 (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
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 ac‐
cepted 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,
glReadPixels, glScissor, glStencilFunc
GLDRAWPIXELS(3G)
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