 |
Index for
Section 3G |
|
 |
Alphabetical
listing for G |
|
 |
Bottom of
page |
|
glDrawPixels(3G)
NAME
glDrawPixels - write a block of pixels to the frame buffer
SYNOPSIS
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 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 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.
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
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.
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 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.
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 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.
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
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 centers 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 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(3), glBlendFunc(3), glCopyPixels(3), glDepthFunc(3),
glLogicOp(3), glPixelMap(3), glPixelStore(3), glPixelTransfer(3),
glPixelZoom(3), glRasterPos(3), glReadPixels(3), glScissor,
glStencilFunc(3)
|
Index for
Section 3G |
|
|
Alphabetical
listing for G |
|
 |
Top of
page |
|