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# Tutorial Effects - Function Printing

Back: Mr. Wiggle
Next: Vertex Data

There are various possibilities to alter the vertex positions by mathematical functions.

For the following examples we use a Grid (EX9.Geometry) as input. Set the resolution to about 50x50.

### f(x, y) = z

Create a new z coordinate by x and y. Using the MrWiggle example we could write:

```float2 Frequency = 10;
float2 Phase = 0;
float2 Amplitude = 0.01;

vs2ps VS(
float4 PosO  : POSITION,
float4 TexCd : TEXCOORD0)
{
//declare output struct
vs2ps Out;

//calculate two waves
float2 wave = sin(PosO.xy * Frequency + Phase) * Amplitude;

//set z coordinate
PosO.z = wave.x + wave.y;

//transform position
Out.Pos = mul(PosO, tWVP);

//transform texturecoordinates
Out.TexCd = mul(TexCd, tTex);

return Out;
}```

using a patch like: ### f(u, v) = xyz

Another common type is to calculate a completely new position from the xy coordinates of the grid. This is often called parametric surfaces, where the xy input parameters are called uv.

for example a cone:

```x = v*cos(u)
y = v*sin(u)
z = v```

can be written as a function:

```float3 Cone(float2 uv)
{
float u = uv.x;
float v = uv.y;

float3 newPos;
newPos.x = v * cos(u);
newPos.y = v * sin(u);
newPos.z = v;

return newPos;
}```

It might be handy to scale u by two pi to get a full cycle in the range 0..1, as well as have a general offset and scale for the input parameters. The vertex shader could then look like:

```#define twopi 6.28318531

float2 Scale = 1;
float2 Offset = 0;

float3 Cone(float2 uv)
{

uv *= Scale;
uv += Offset;

float u = uv.x * twopi;
float v = uv.y;

float3 newPos;
newPos.x = v * cos(u);
newPos.y = v * sin(u);
newPos.z = v;

return newPos;
}

vs2ps VS(
float4 PosO  : POSITION,
float4 TexCd : TEXCOORD0)
{
//declare output struct
vs2ps Out;

//set new position
PosO.xyz = Cone(PosO.xy);

//transform position
Out.Pos = mul(PosO, tWVP);

//transform texturecoordinates
Out.TexCd = mul(TexCd, tTex);

return Out;
}```

And the patch: Next: Vertex Data
Back: Mr. Wiggle

# Shoutbox

~6d ago

~11d ago

SuperflysiNZ: Thanks

~12d ago

~13d ago

sebescudie: @Superfly : ApplicationPath

~14d ago

SuperflysiNZ: How do you get the path of the current patch in VL?

~14d ago

SuperflysiNZ: How do you get the path of the current patch in VL?

~14d ago

joreg: reminder: first #vvvv online meetup after the summer break: tomorrow, tuesday 7th, 8pm CET 13.-worldwide-vvvv-meetup