GLDRAWPIXELS
Section: Misc. Reference Manual Pages (3G)
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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 )
delim $$
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 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 pixels 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,
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 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 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$~ times ~$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 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 ,
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 $2 sup b -1$,
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 $n$th fragment such that
-
$x sub n ~=~ x sub r ~+~ n ~ roman mod ~ "width"$
$y sub n ~=~ y sub r ~+~ |_ n ^/^ "width" ~ _|$
-
where ($x sub r , y sub r$) 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 ,
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 $2 sup b -1$,
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 $n$th index is written to location
-
$x sub n ~=~ x sub r ~+~ n ~ roman mod ~ "width"$
$y sub n ~=~ y sub r ~+~ |_ ~ n / "width" ~ _|$
-
where ($x sub r , y sub r$) 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
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 $n$th fragment such that
-
$x sub n ~=~ x sub r ~+~ n ~ roman mod ~ "width"$
$y sub n ~=~ y sub r ~+~ |_ ~ n / "width" ~ _|$
-
where ($x sub r , y sub r$) 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
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 coordinates to the $n$th fragment such that
-
$x sub n ~=~ x sub r ~+~ n ~ roman mod ~ "width"$
$y sub n ~=~ y sub r ~+~ |_ ~ n / "width" ~ _|$
-
where ($x sub r , y sub r$) 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 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 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 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 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 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 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 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 ($x sub r$, $y sub r$) is the current raster position,
and a given pixel is in the $n$th column and $m$th row
of the pixel rectangle,
then fragments are generated for pixels whose centers are in the rectangle
with corners at
-
($x sub r ~+~ zoom sub x^ n$, $y sub r ~+~ zoom sub y^ m$)
($x sub r ~+~ zoom sub x^ (n ~+~ 1)$, $y sub r ~+~ zoom sub y^ ( m ~+~ 1 )$)
where $zoom sub x$ is the value of GL_ZOOM_X and
$zoom sub y$ 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 format 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)