glDrawPixels(3G)glDrawPixels(3G)NAMEglDrawPixels - write a block of pixels to the frame buffer
SYNOPSIS
void glDrawPixels(
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const GLvoid *pixels );
PARAMETERS
Specify the dimensions of the pixel rectangle to be written into the
frame buffer. 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. Specifies the data type for pix‐
els. 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. Specifies a pointer to the pixel data.
DESCRIPTIONglDrawPixels() 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 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 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, inte‐
gers, 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, spec‐
ified 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 times height pixels are read from memory, starting at location
pixels. By default, these pixels are taken from adjacent memory loca‐
tions, 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 parame‐
ters specify different read pointer advancements, both before the first
pixel is read and after all width pixels are read. See the glPixel‐
Store() reference page for details on these options.
The width times height pixels that are read from memory are each oper‐
ated 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 of the pixels, as specified by format.
format can assume one of 13 symbolic values: Each pixel is a single
value, a color index. It is converted to fixed-point , with an unspeci‐
fied 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 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 2 sup 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
mod width
y[n] = y[r] + floor 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. Each pixel is a single value,
a stencil index. It is converted 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 con‐
vert 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 nega‐
tive, 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 sup 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 mod width
y[n] = y[r] + floor 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. Each pixel is a sin‐
gle-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 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
mod width
y[n] = y[r] + floor 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. 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 with
unspecified precision. Signed integer values are mapped linearly
to the internal floating-point such that the most positive rep‐
resentable integer value maps to 1.0, and the most negative rep‐
resentable 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 multi‐
plied 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 x[n] = x[r] + n mod width
y[n] = y[r] + floor n/width floor
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. Each pixel is a single red
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 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. Each pixel is a single
green component. This component is converted 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. Each
pixel is a single blue component. This component is converted 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 conver‐
sion, the pixel is treated as if it had been read as an RGBA
pixel. Each pixel is a single alpha component. This component
is converted 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 con‐
version, the pixel is treated as if it had been read as an RGBA
pixel. Each pixel is a three-component group: red first, fol‐
lowed by green, followed by blue; for GL_BGR, the first compo‐
nent is blue, followed by green and then red. Each component is
converted 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. 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 con‐
verted to an RGBA pixel with red, green, and blue set to the
converted luminance value, and alpha set to 1. After this con‐
version, the pixel is treated as if it had been read as an RGBA
pixel. 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
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 cen‐
ters are in the rectangle with corners at
(x[r] + zoom[x] n, y[r] + zoom[y] m)
(x[r] + zoom[x] (n + 1), y[r] + zoom[y] ( m + 1 ))
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_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 GETSglGet() with argument GL_CURRENT_RASTER_POSITION
glGet() with argument GL_CURRENT_RASTER_POSITION_VALID
SEE ALSOglAlphaFunc(3), glBlendFunc(3), glCopyPixels(3), glDepthFunc(3),
glLogicOp(3), glPixelMap(3), glPixelStore(3), glPixelTransfer(3),
glPixelZoom(3), glRasterPos(3), glReadPixels(3), glScissor, glStencil‐
Func(3)glDrawPixels(3G)