Gambas Documentation - /comp/gb.opengl/gl/drawpixels

/comp/gb.opengl/gl/drawpixels

# Gl.DrawPixels (gb.opengl)

Static Sub DrawPixels ( Image As Image )

Write a block of pixels to the frame buffer.

### 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

Gl.DrawPixels 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 Gl.RasterPos or Gl.WindowPos to set the current raster position; use Gl.Get with argument Gl.CURRENT_RASTER_POSITION_VALID to determine if the specified raster position is valid, and Gl.Get 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: Gl.PixelStore, Gl.PixelTransfer, Gl.PixelMap, and Gl.PixelZoom. This reference page describes the effects on Gl.DrawPixels 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 Gl.PixelStore).

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 Gl.PixelStore 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 Gl.PixelStore reference page for details on these options.

If a non-zero named buffer object is bound to the Gl.PIXEL_UNPACK_BUFFER target (see Gl.BindBuffer) 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 Gl.PixelTransfer and Gl.PixelMap. 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 Gl.PixelZoom 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 Gl.DrawPixels is executed between the execution of Gl.Begin and the corresponding execution of Gl.End.

### Associated Gets

Gl.Get with argument Gl.CURRENT_RASTER_POSITION

Gl.Get with argument Gl.CURRENT_RASTER_POSITION_VALID

Gl.Get with argument Gl.PIXEL_UNPACK_BUFFER_BINDING

### See also

- Gl.AlphaFunc,

- Gl.BlendFunc,

- Gl.CopyPixels,

- Gl.DepthFunc,

Gl.LogicOp, Gl.PixelMap, Gl.PixelStore, Gl.PixelTransfer, Gl.PixelZoom, Gl.RasterPos, Gl.ReadPixels, Gl.Scissor,

- Gl.StencilFunc,

Gl.WindowPos

See original documentation on OpenGL website