Gl.TexParameterf (gb.opengl)

Static Sub TexParameterf ( Target As Integer, Pname As Integer, Param As Float )

Set texture parameters.

Parameters

target: Specifies the target texture, which must be either Gl.TEXTURE_1D, Gl.TEXTURE_2D, Gl.TEXTURE_3D, Gl.TEXTURE_1D_ARRAY, Gl.TEXTURE_2D_ARRAY, Gl.TEXTURE_RECTANGLE, or Gl.TEXTURE_CUBE_MAP.
pname: Specifies the symbolic name of a single-valued texture parameter. pname can be one of the following: Gl.TEXTURE_BASE_LEVEL, Gl.TEXTURE_COMPARE_FUNC, Gl.TEXTURE_COMPARE_MODE, Gl.TEXTURE_LOD_BIAS, Gl.TEXTURE_MIN_FILTER, Gl.TEXTURE_MAG_FILTER, Gl.TEXTURE_MIN_LOD, Gl.TEXTURE_MAX_LOD, Gl.TEXTURE_MAX_LEVEL, Gl.TEXTURE_SWIZZLE_R, Gl.TEXTURE_SWIZZLE_G, Gl.TEXTURE_SWIZZLE_B, Gl.TEXTURE_SWIZZLE_A, Gl.TEXTURE_WRAP_S, Gl.TEXTURE_WRAP_T, or Gl.TEXTURE_WRAP_R.
param: Specifies the value of pname.

Parameters

target: Specifies the target texture, which must be either Gl.TEXTURE_1D, Gl.TEXTURE_2D, Gl.TEXTURE_3D, Gl.TEXTURE_1D_ARRAY, Gl.TEXTURE_2D_ARRAY, Gl.TEXTURE_RECTANGLE, or Gl.TEXTURE_CUBE_MAP.
pname: Specifies the symbolic name of a texture parameter. pname can be one of the following: Gl.TEXTURE_BASE_LEVEL, Gl.TEXTURE_BORDER_COLOR, Gl.TEXTURE_COMPARE_FUNC, Gl.TEXTURE_COMPARE_MODE, Gl.TEXTURE_LOD_BIAS, Gl.TEXTURE_MIN_FILTER, Gl.TEXTURE_MAG_FILTER, Gl.TEXTURE_MIN_LOD, Gl.TEXTURE_MAX_LOD, Gl.TEXTURE_MAX_LEVEL, Gl.TEXTURE_SWIZZLE_R, Gl.TEXTURE_SWIZZLE_G, Gl.TEXTURE_SWIZZLE_B, Gl.TEXTURE_SWIZZLE_A, Gl.TEXTURE_SWIZZLE_RGBA, Gl.TEXTURE_WRAP_S, Gl.TEXTURE_WRAP_T, or Gl.TEXTURE_WRAP_R.
params: Specifies a pointer to an array where the value or values of pname are stored.

Description

Gl.TexParameter assigns the value or values in params to the texture parameter specified as pname. target defines the target texture, either Gl.TEXTURE_1D, Gl.TEXTURE_2D, Gl.TEXTURE_1D_ARRAY, Gl.TEXTURE_2D_ARRAY, Gl.TEXTURE_RECTANGLE, or Gl.TEXTURE_3D. The following symbols are accepted in pname:

Gl.TEXTURE_BASE_LEVEL: Specifies the index of the lowest defined mipmap level. This is an integer value. The initial value is 0.

Gl.TEXTURE_BORDER_COLOR

The data in params specifies four values that define the border values that should be used for border texels. If a texel is sampled from the border of the texture, the values of Gl.TEXTURE_BORDER_COLOR are interpreted as an RGBA color to match the texture's internal format and substituted for the non-existent texel data. If the texture contains depth components, the first component of Gl.TEXTURE_BORDER_COLOR is interpreted as a depth value. The initial value is

(0.0, 0.0, 0.0, 0.0)

If the values for Gl.TEXTURE_BORDER_COLOR are specified with Gl.TexParameterIiv or Gl.TexParameterIuiv, the values are stored unmodified with an internal data type of integer. If specified with Gl.TexParameteriv, they are converted to floating point with the following equation:

f \frac{2_{c} + 1}{2^{b} - 1}

. If specified with Gl.TexParameterfv, they are stored unmodified as floating-point values.

Gl.TEXTURE_COMPARE_FUNC

Specifies the comparison operator used when Gl.TEXTURE_COMPARE_MODE is set to Gl.COMPARE_REF_TO_TEXTURE. Permissible values are:

Texture Comparison Function	Computed result
Gl.LEQUAL	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r < D_{t} \\ r > D_{t} \end{matrix}$
Gl.GEQUAL	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r > D_{t} \\ r < D_{t} \end{matrix}$
Gl.LESS	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r < D_{t} \\ r > D_{t} \end{matrix}$
Gl.GREATER	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r > D_{t} \\ r < D_{t} \end{matrix}$
Gl.EQUAL	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r D_{t} \\ r \neq D_{t} \end{matrix}$
Gl.NOTEQUAL	$result \{\begin{matrix} 1.0 \\ 0.0 \end{matrix} \begin{matrix} r \neq D_{t} \\ r D_{t} \end{matrix}$
Gl.ALWAYS	$result 1.0$
Gl.NEVER	$result 0.0$

where

r

is the current interpolated texture coordinate, and

D_{t}

is the depth texture value sampled from the currently bound depth texture.

result

is assigned to the the red channel.

Gl.TEXTURE_COMPARE_MODE

Specifies the texture comparison mode for currently bound depth textures. That is, a texture whose internal format is Gl.DEPTH_COMPONENT_; see Gl.TexImage2D) Permissible values are:

Gl.COMPARE_REF_TO_TEXTURE: Specifies that the interpolated and clamped $r$ texture coordinate should be compared to the value in the currently bound depth texture. See the discussion of Gl.TEXTURE_COMPARE_FUNC for details of how the comparison is evaluated. The result of the comparison is assigned to the red channel.
Gl.NONE: Specifies that the red channel should be assigned the appropriate value from the currently bound depth texture.

Gl.TEXTURE_LOD_BIAS

params specifies a fixed bias value that is to be added to the level-of-detail parameter for the texture before texture sampling. The specified value is added to the shader-supplied bias value (if any) and subsequently clamped into the implementation-defined range

[/]

bias max bias max , where

{bias}_{\max}

is the value of the implementation defined constant Gl.MAX_TEXTURE_LOD_BIAS. The initial value is 0.0.

Gl.TEXTURE_MIN_FILTER

The texture minifying function is used whenever the level-of-detail function used when sampling from the texture determines that the texture should be minified. There are six defined minifying functions. Two of them use either the nearest texture elements or a weighted average of multiple texture elements to compute the texture value. The other four use mipmaps.

A mipmap is an ordered set of arrays representing the same image at progressively lower resolutions. If the texture has dimensions

2^{n} \times 2^{m}

, there are

\max (n, m) + 1

mipmaps. The first mipmap is the original texture, with dimensions

2^{n} \times 2^{m}

. Each subsequent mipmap has dimensions

2^{k - 1} \times 2^{l - 1}

, where

2^{k} \times 2^{l}

are the dimensions of the previous mipmap, until either

k 0

l 0

. At that point, subsequent mipmaps have dimension

1 \times 2^{l - 1}

2^{k - 1} \times 1

until the final mipmap, which has dimension

1 \times 1

. To define the mipmaps, call Gl.TexImage1D, Gl.TexImage2D, Gl.TexImage3D, Gl.CopyTexImage1D, or Gl.CopyTexImage2D with the level argument indicating the order of the mipmaps. Level 0 is the original texture; level

\max (n, m)

is the final

1 \times 1

mipmap.

params supplies a function for minifying the texture as one of the following:

Gl.NEAREST: Returns the value of the texture element that is nearest (in Manhattan distance) to the specified texture coordinates.
Gl.LINEAR: Returns the weighted average of the four texture elements that are closest to the specified texture coordinates. These can include items wrapped or repeated from other parts of a texture, depending on the values of Gl.TEXTURE_WRAP_S and Gl.TEXTURE_WRAP_T, and on the exact mapping.
Gl.NEAREST_MIPMAP_NEAREST: Chooses the mipmap that most closely matches the size of the pixel being textured and uses the Gl.NEAREST criterion (the texture element closest to the specified texture coordinates) to produce a texture value.
Gl.LINEAR_MIPMAP_NEAREST: Chooses the mipmap that most closely matches the size of the pixel being textured and uses the Gl.LINEAR criterion (a weighted average of the four texture elements that are closest to the specified texture coordinates) to produce a texture value.
Gl.NEAREST_MIPMAP_LINEAR: Chooses the two mipmaps that most closely match the size of the pixel being textured and uses the Gl.NEAREST criterion (the texture element closest to the specified texture coordinates ) to produce a texture value from each mipmap. The final texture value is a weighted average of those two values.
Gl.LINEAR_MIPMAP_LINEAR: Chooses the two mipmaps that most closely match the size of the pixel being textured and uses the Gl.LINEAR criterion (a weighted average of the texture elements that are closest to the specified texture coordinates) to produce a texture value from each mipmap. The final texture value is a weighted average of those two values.

As more texture elements are sampled in the minification process, fewer aliasing artifacts will be apparent. While the Gl.NEAREST and Gl.LINEAR minification functions can be faster than the other four, they sample only one or multiple texture elements to determine the texture value of the pixel being rendered and can produce moire patterns or ragged transitions. The initial value of Gl.TEXTURE_MIN_FILTER is Gl.NEAREST_MIPMAP_LINEAR.

Gl.TEXTURE_MAG_FILTER

The texture magnification function is used whenever the level-of-detail function used when sampling from the texture determines that the texture should be magified. It sets the texture magnification function to either Gl.NEAREST or Gl.LINEAR (see below). Gl.NEAREST is generally faster than Gl.LINEAR, but it can produce textured images with sharper edges because the transition between texture elements is not as smooth. The initial value of Gl.TEXTURE_MAG_FILTER is Gl.LINEAR.

Gl.NEAREST: Returns the value of the texture element that is nearest (in Manhattan distance) to the specified texture coordinates.
Gl.LINEAR: Returns the weighted average of the texture elements that are closest to the specified texture coordinates. These can include items wrapped or repeated from other parts of a texture, depending on the values of Gl.TEXTURE_WRAP_S and Gl.TEXTURE_WRAP_T, and on the exact mapping.

Gl.TEXTURE_MIN_LOD: Sets the minimum level-of-detail parameter. This floating-point value limits the selection of highest resolution mipmap (lowest mipmap level). The initial value is -1000.

Gl.TEXTURE_MAX_LOD: Sets the maximum level-of-detail parameter. This floating-point value limits the selection of the lowest resolution mipmap (highest mipmap level). The initial value is 1000.

Gl.TEXTURE_MAX_LEVEL: Sets the index of the highest defined mipmap level. This is an integer value. The initial value is 1000.

Gl.TEXTURE_SWIZZLE_R: Sets the swizzle that will be applied to the $r$ component of a texel before it is returned to the shader. Valid values for param are Gl.RED, Gl.GREEN, Gl.BLUE, Gl.ALPHA, Gl.ZERO and Gl.ONE. If Gl.TEXTURE_SWIZZLE_R is Gl.RED, the value for $r$ will be taken from the first channel of the fetched texel. If Gl.TEXTURE_SWIZZLE_R is Gl.GREEN, the value for $r$ will be taken from the second channel of the fetched texel. If Gl.TEXTURE_SWIZZLE_R is Gl.BLUE, the value for $r$ will be taken from the third channel of the fetched texel. If Gl.TEXTURE_SWIZZLE_R is Gl.ALPHA, the value for $r$ will be taken from the fourth channel of the fetched texel. If Gl.TEXTURE_SWIZZLE_R is Gl.ZERO, the value for $r$ will be subtituted with $0.0$ . If Gl.TEXTURE_SWIZZLE_R is Gl.ONE, the value for $r$ will be subtituted with $1.0$ . The initial value is Gl.RED.

Gl.TEXTURE_SWIZZLE_G: Sets the swizzle that will be applied to the $g$ component of a texel before it is returned to the shader. Valid values for param and their effects are similar to those of Gl.TEXTURE_SWIZZLE_R. The initial value is Gl.GREEN.

Gl.TEXTURE_SWIZZLE_B: Sets the swizzle that will be applied to the $b$ component of a texel before it is returned to the shader. Valid values for param and their effects are similar to those of Gl.TEXTURE_SWIZZLE_R. The initial value is Gl.BLUE.

Gl.TEXTURE_SWIZZLE_A: Sets the swizzle that will be applied to the $a$ component of a texel before it is returned to the shader. Valid values for param and their effects are similar to those of Gl.TEXTURE_SWIZZLE_R. The initial value is Gl.ALPHA.

Gl.TEXTURE_SWIZZLE_RGBA: Sets the swizzles that will be applied to the $r$ , $g$ , $b$ , and $a$ components of a texel before they are returned to the shader. Valid values for params and their effects are similar to those of Gl.TEXTURE_SWIZZLE_R, except that all channels are specified simultaneously. Setting the value of Gl.TEXTURE_SWIZZLE_RGBA is equivalent (assuming no errors are generated) to setting the parameters of each of Gl.TEXTURE_SWIZZLE_R, Gl.TEXTURE_SWIZZLE_G, Gl.TEXTURE_SWIZZLE_B, and Gl.TEXTURE_SWIZZLE_A successively.

Gl.TEXTURE_WRAP_S: Sets the wrap parameter for texture coordinate $s$ to either Gl.CLAMP_TO_EDGE, Gl.CLAMP_TO_BORDER, Gl.MIRRORED_REPEAT, or Gl.REPEAT. Gl.CLAMP_TO_EDGE causes $s$ coordinates to be clamped to the range $[/\frac{1}{2N}, 1 - \frac{1}{2N}]$ , where $N$ is the size of the texture in the direction of clamping. Gl.CLAMP_TO_BORDER evaluates $s$ coordinates in a similar manner to Gl.CLAMP_TO_EDGE. However, in cases where clamping would have occurred in Gl.CLAMP_TO_EDGE mode, the fetched texel data is substituted with the values specified by Gl.TEXTURE_BORDER_COLOR. Gl.REPEAT causes the integer part of the $s$ coordinate to be ignored; the GL uses only the fractional part, thereby creating a repeating pattern. Gl.MIRRORED_REPEAT causes the $s$ coordinate to be set to the fractional part of the texture coordinate if the integer part of $s$ is even; if the integer part of $s$ is odd, then the $s$ texture coordinate is set to $1 - frac (s)$ , where $frac (s)$ represents the fractional part of $s$ . Initially, Gl.TEXTURE_WRAP_S is set to Gl.REPEAT.

Gl.TEXTURE_WRAP_T: Sets the wrap parameter for texture coordinate $t$ to either Gl.CLAMP_TO_EDGE, Gl.CLAMP_TO_BORDER, Gl.MIRRORED_REPEAT, or Gl.REPEAT. See the discussion under Gl.TEXTURE_WRAP_S. Initially, Gl.TEXTURE_WRAP_T is set to Gl.REPEAT.

Gl.TEXTURE_WRAP_R: Sets the wrap parameter for texture coordinate $r$ to either Gl.CLAMP_TO_EDGE, Gl.CLAMP_TO_BORDER, Gl.MIRRORED_REPEAT, or Gl.REPEAT. See the discussion under Gl.TEXTURE_WRAP_S. Initially, Gl.TEXTURE_WRAP_R is set to Gl.REPEAT.

Notes

Suppose that a program attempts to sample from a texture and has set Gl.TEXTURE_MIN_FILTER to one of the functions that requires a mipmap. If either the dimensions of the texture images currently defined (with previous calls to Gl.TexImage1D, Gl.TexImage2D, Gl.TexImage3D, Gl.CopyTexImage1D, or Gl.CopyTexImage2D) do not follow the proper sequence for mipmaps (described above), or there are fewer texture images defined than are needed, or the set of texture images have differing numbers of texture components, then the texture is considered incomplete.

Linear filtering accesses the four nearest texture elements only in 2D textures. In 1D textures, linear filtering accesses the two nearest texture elements. In 3D textures, linear filtering accesses the eight nearest texture elements.

Gl.TexParameter specifies the texture parameters for the active texture unit, specified by calling Gl.ActiveTexture.

Errors

Gl.INVALID_ENUM is generated if target or pname is not one of the accepted defined values.

Gl.INVALID_ENUM is generated if params should have a defined constant value (based on the value of pname) and does not.

Associated Gets

Gl.GetTexParameter

Gl.GetTexLevelParameter

Gl.TexParameterf (gb.opengl)

Parameters

Parameters

Description

Notes

Errors

Associated Gets

See also