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TOC: Of Effects and Shaders

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.

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:

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

TOC: Of Effects and Shaders

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