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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 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.
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 com-ponent, component,
ponent, 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 compo-nents, components,
nents, specified by format, for a single pixel in a reversed order. Indices are always treated indi-vidually. individually.
vidually. 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 * 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 specific to the format
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 inte-ger integer
ger 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 inte-ger integer
ger part of the index is then ANDed with (2^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
xn = xr + n mod width
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 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 inte-ger integer
ger 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 inte-ger integer
ger part of the index is then ANDed with (2^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
xn = xr + n mod width
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 floatingpoint
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
xn = xr + n mod width
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_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 float-ing-point floating-point
ing-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 compo-nents. components.
nents. 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 nth fragment such that
xn = xr + n mod width
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_RED Each pixel is a single red component. This component is converted to the internal floating-point floatingpoint
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 floatingpoint
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 floatingpoint
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 floatingpoint
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 converted
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 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 con-verted converted
verted 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 rectan-gle rectangle
gle with corners at
( xr + zoomx * n, yr + zoomy *m)
( 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 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)
GLDRAWPIXELS(3G)
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