OpenGL man pages
glDrawPixels - write a block of pixels to the frame buffer
void glDrawPixels( GLsizei width, GLsizei height, GLenum format, GLenum type, const GLvoid *pixels )
width, height Specify the dimensions of the pixel rectangle that will 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_RGBA, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, 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, and GL_FLOAT are accepted. pixels Specifies a pointer to the pixel data.
glDrawPixels reads pixel data from memory and writes it into the frame
buffer relative to the current raster position. Use glRasterPos to set the
current raster position, and use 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. Each of these bytes, shorts,
integers, or floating-point values is interpreted as one color or depth
component, or one index, depending on format. 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).
widthxheight 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. Refer to the glPixelStore reference page for
details on these options.
The widthxheight 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
eleven 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 values. Signed
and unsigned integer data is converted with all fraction bits set
to zero. Bitmap data convert to either 0.0 or 1.0.
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 using 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
b
2 -1, where b is the number of bits in a color index buffer.
The resulting indices or RGBA colors are then converted 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 = x + n mod width
n r
y = y + floor (n/width)
n r
where (x ,y ) is the current raster position. These pixel
r r
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 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 values. Signed
and unsigned integer data is converted with all fraction bits set
to zero. Bitmap data convert to either 0.0 or 1.0.
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
b
of the index is then ANDed with 2 -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 = x + n mod width
n r
y = y + floor (n/width)
n r
where (x ,y ) is the current raster position. Only the pixel
r r
ownership test, the scissor test, and the stencil writemask affect
these writes.
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 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 zero 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 resulting depth components are then converted 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 = x + n mod width
n r
y = y + floor (n/width)
n r
where (x ,y ) is the current raster position. These pixel fragments
r r
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
Each pixel is a four-component group: red first, followed by green,
followed by blue, followed by alpha. Floating-point values are
converted directly to an internal floating-point format with
unspecified precision. Signed integer values are 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 zero 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 resulting RGBA colors are then converted 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 = x + n mod width
n r
y = y + floor (n/width)
n r
where (x ,y ) is the current raster position. These pixel fragments
r r
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 format in the same way as the red
component of an RGBA pixel is, then it is converted to an RGBA pixel
with green and blue set to 0.0, and alpha set to 1.0. After this
conversion, the pixel is treated just 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 format in the same way as the green
component of an RGBA pixel is, then it is converted to an RGBA pixel
with red and blue set to 0.0, and alpha set to 1.0. After this
conversion, the pixel is treated just 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 format in the same way as the blue
component of an RGBA pixel is, then it is converted to an RGBA pixel
with red and green set to 0.0, and alpha set to 1.0. After this
conversion, the pixel is treated just 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 format in the same way as the alpha
component of an RGBA pixel is, then it is converted to an RGBA pixel
with red, green, and blue set to 0.0. After this conversion, the
pixel is treated just as if it had been read as an RGBA pixel.
GL_RGB
Each pixel is a three-component group: red first, followed by green,
followed by blue. Each component is converted to the internal
floating-point format in the same way as the red, green, and blue
components of an RGBA pixel are. The color triple is converted to an
RGBA pixel with alpha set to 1.0. After this conversion, the pixel is
treated just 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 as the
red component of an RGBA pixel is, then it is converted to an RGBA
pixel with red, green, and blue set to the converted luminance value,
and alpha set to 1.0. After this conversion, the pixel is treated
just 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 as the red component of an RGBA pixel is,
then they are 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 just 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 |
-------------------------------------------------------------
The rasterization described thus far assumes pixel zoom factors of 1.0. If
glPixelZoom is used to change the x and y pixel zoom factors, pixels are
converted to fragments as follows. If (x , y ) is the current raster
r r
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
(x + zoom n, y + zoom m)
r x r y
(x + zoom (n+1), y + zoom (m+1))
r x r y
where zoom is the value of GL_ZOOM_X and zoom is the value of GL_ZOOM_Y.
x y
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_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.
glGet with argument GL_CURRENT_RASTER_POSITION glGet with argument GL_CURRENT_RASTER_POSITION_VALID
glAlphaFunc, glBlendFunc, glCopyPixels, glDepthFunc, glLogicOp, glPixelMap, glPixelStore, glPixelTransfer, glPixelZoom, glRasterPos, glReadPixels, glScissor, glStencilFunc
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Last Edited:
Fri Dec 6 11:18:03 EST 1996
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