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# docs.GL

OpenGL 3
OpenGL 2

# glDrawPixels

## 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 * | data`)`;

## 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 `data`. 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.

`data`

  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 or glWindowPos 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 `data` 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`, or `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`, or `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 × height pixels are read from memory, starting at location `data`. 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.

If a non-zero named buffer object is bound to the `GL_PIXEL_UNPACK_BUFFER` target (see glBindBuffer) while a block of pixels is specified, `data` is treated as a byte offset into the buffer object's data store.

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 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 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 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 % width

  y n = y r + 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 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 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 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 % width

  y n = y r + 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 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 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 % width

  y n = y r + 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 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 . (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 % width

  y n = y r + 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_RED`

  Each pixel is a single red component. This component is converted to the internal floating-point format 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 format 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 format 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 format 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 format 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 format 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 format 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 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_ENUM` is generated if `format` or `type` is not one of the accepted values.

`GL_INVALID_ENUM` is generated if `type` is `GL_BITMAP` and `format` is not either `GL_COLOR_INDEX` or `GL_STENCIL_INDEX`.

`GL_INVALID_VALUE` is generated if either `width` or `height` is negative.

`GL_INVALID_OPERATION` is generated if `format` is `GL_STENCIL_INDEX` and there is no stencil buffer.

`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_OPERATION` is generated if `format` is one of `GL_UNSIGNED_BYTE_3_3_2`, `GL_UNSIGNED_BYTE_2_3_3_REV`, `GL_UNSIGNED_SHORT_5_6_5`, or `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`.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and the buffer object's data store is currently mapped.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and the data would be unpacked from the buffer object such that the memory reads required would exceed the data store size.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and `data` is not evenly divisible into the number of bytes needed to store in memory a datum indicated by `type`.

`GL_INVALID_OPERATION` is generated if `glDrawPixels` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGet with argument `GL_CURRENT_RASTER_POSITION`

glGet with argument `GL_CURRENT_RASTER_POSITION_VALID`

glGet with argument `GL_PIXEL_UNPACK_BUFFER_BINDING`

## See Also

glAlphaFunc, glBlendFunc, glCopyPixels, glDepthFunc, glLogicOp, glPixelMap, glPixelStore, glPixelTransfer, glPixelZoom, glRasterPos, glReadPixels, glScissor, glStencilFunc, glWindowPos

## Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/.

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