Gl.Map1f (gb.opengl)

Static Sub Map1f ( Target As Integer, U1 As Float, U2 As Float, Stride As Integer, Order As Integer, Points As Float[] )

Define a one-dimensional evaluator.

Parameters

target: Specifies the kind of values that are generated by the evaluator. Symbolic constants Gl.MAP1_VERTEX_3, Gl.MAP1_VERTEX_4, Gl.MAP1_INDEX, Gl.MAP1_COLOR_4, Gl.MAP1_NORMAL, Gl.MAP1_TEXTURE_COORD_1, Gl.MAP1_TEXTURE_COORD_2, Gl.MAP1_TEXTURE_COORD_3, and Gl.MAP1_TEXTURE_COORD_4 are accepted.
u1, u2: Specify a linear mapping of $u$ , as presented to Gl.EvalCoord1, to $\hat{u}$ , the variable that is evaluated by the equations specified by this command.
stride: Specifies the number of floats or doubles between the beginning of one control point and the beginning of the next one in the data structure referenced in points. This allows control points to be embedded in arbitrary data structures. The only constraint is that the values for a particular control point must occupy contiguous memory locations.
order: Specifies the number of control points. Must be positive.
points: Specifies a pointer to the array of control points.

Description

Evaluators provide a way to use polynomial or rational polynomial mapping to produce vertices, normals, texture coordinates, and colors. The values produced by an evaluator are sent to further stages of GL processing just as if they had been presented using Gl.Vertex, Gl.Normal, Gl.TexCoord, and Gl.Color commands, except that the generated values do not update the current normal, texture coordinates, or color.

All polynomial or rational polynomial splines of any degree (up to the maximum degree supported by the GL implementation) can be described using evaluators. These include almost all splines used in computer graphics: B-splines, Bezier curves, Hermite splines, and so on.

Evaluators define curves based on Bernstein polynomials. Define

p (\hat{u})

p (\hat{u}) Σ_{i 0}^{n} {B_{i}}^{n} (\hat{u}) R_{i}

where

R_{i}

is a control point and

{B_{i}}^{n} (\hat{u})

is the

i

th Bernstein polynomial of degree

n

(order =

n + 1

{B_{i}}^{n} (\hat{u}) (\begin{matrix} n \\ i \end{matrix}) {\hat{u}}^{i} {(1 - \hat{u})}^{n - i}

Recall that

0^{0} 1

and

(\begin{matrix} n \\ 0 \end{matrix}) 1

Gl.Map1 is used to define the basis and to specify what kind of values are produced. Once defined, a map can be enabled and disabled by calling Gl.Enable and Gl.Disable with the map name, one of the nine predefined values for target described below. Gl.EvalCoord1 evaluates the one-dimensional maps that are enabled. When Gl.EvalCoord1 presents a value

u

, the Bernstein functions are evaluated using

\hat{u}

, where

\hat{u} \frac{u - u1}{u2 - u1}

target is a symbolic constant that indicates what kind of control points are provided in points, and what output is generated when the map is evaluated. It can assume one of nine predefined values:

Gl.MAP1_VERTEX_3: Each control point is three floating-point values representing $x$ , $y$ , and $z$ . Internal Gl.Vertex3 commands are generated when the map is evaluated.
Gl.MAP1_VERTEX_4: Each control point is four floating-point values representing $x$ , $y$ , $z$ , and $w$ . Internal Gl.Vertex4 commands are generated when the map is evaluated.
Gl.MAP1_INDEX: Each control point is a single floating-point value representing a color index. Internal Gl.Index commands are generated when the map is evaluated but the current index is not updated with the value of these Gl.Index commands.
Gl.MAP1_COLOR_4: Each control point is four floating-point values representing red, green, blue, and alpha. Internal Gl.Color4 commands are generated when the map is evaluated but the current color is not updated with the value of these Gl.Color4 commands.
Gl.MAP1_NORMAL: Each control point is three floating-point values representing the $x$ , $y$ , and $z$ components of a normal vector. Internal Gl.Normal commands are generated when the map is evaluated but the current normal is not updated with the value of these Gl.Normal commands.
Gl.MAP1_TEXTURE_COORD_1: Each control point is a single floating-point value representing the $s$ texture coordinate. Internal Gl.TexCoord1 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these Gl.TexCoord commands.
Gl.MAP1_TEXTURE_COORD_2: Each control point is two floating-point values representing the $s$ and $t$ texture coordinates. Internal Gl.TexCoord2 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these Gl.TexCoord commands.
Gl.MAP1_TEXTURE_COORD_3: Each control point is three floating-point values representing the $s$ , $t$ , and $r$ texture coordinates. Internal Gl.TexCoord3 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these Gl.TexCoord commands.
Gl.MAP1_TEXTURE_COORD_4: Each control point is four floating-point values representing the $s$ , $t$ , $r$ , and $q$ texture coordinates. Internal Gl.TexCoord4 commands are generated when the map is evaluated but the current texture coordinates are not updated with the value of these Gl.TexCoord commands.

stride, order, and points define the array addressing for accessing the control points. points is the location of the first control point, which occupies one, two, three, or four contiguous memory locations, depending on which map is being defined. order is the number of control points in the array. stride specifies how many float or double locations to advance the internal memory pointer to reach the next control point.

Notes

As is the case with all GL commands that accept pointers to data, it is as if the contents of points were copied by Gl.Map1 before Gl.Map1 returns. Changes to the contents of points have no effect after Gl.Map1 is called.

Errors

Gl.INVALID_ENUM is generated if target is not an accepted value.

Gl.INVALID_VALUE is generated if u1 is equal to u2.

Gl.INVALID_VALUE is generated if stride is less than the number of values in a control point.

Gl.INVALID_VALUE is generated if order is less than 1 or greater than the return value of Gl.MAX_EVAL_ORDER.

Gl.INVALID_OPERATION is generated if Gl.Map1 is executed between the execution of Gl.Begin and the corresponding execution of Gl.End.

Gl.INVALID_OPERATION is generated if Gl.Map1 is called and the value of Gl.ACTIVE_TEXTURE is not Gl.TEXTURE0.

Associated Gets

Gl.GetMap

Gl.Get with argument Gl.MAX_EVAL_ORDER

Gl.IsEnabled with argument Gl.MAP1_VERTEX_3

Gl.IsEnabled with argument Gl.MAP1_VERTEX_4

Gl.IsEnabled with argument Gl.MAP1_INDEX

Gl.IsEnabled with argument Gl.MAP1_COLOR_4

Gl.IsEnabled with argument Gl.MAP1_NORMAL

Gl.IsEnabled with argument Gl.MAP1_TEXTURE_COORD_1

Gl.IsEnabled with argument Gl.MAP1_TEXTURE_COORD_2

Gl.IsEnabled with argument Gl.MAP1_TEXTURE_COORD_3