Posted By: ventilator
waving grass - 10/01/03 05:13
i adapted the waving grass shader which can be found at the ati website for a6!
Code:
use some intersecting quads as grass model. the grass texture should be a tga bitmap with alphachannel. the polygons will be rendered two-sided.
there are a lot of parameters to tweak (c40-c47) and i am sure it's possible to achieve nicer motion than with my settings!
Code:
texture texSkin1;
matrix matWorldViewProj;
matrix matWorldView;
vector vecFog;
vector vecTime;
technique grass
{
pass p0
{
Texture[0]=<texSkin1>;
ZWriteEnable=true;
AlphaTestEnable=true;
CullMode=none;
VertexShaderConstant[0]=<matWorldViewProj>;
VertexShaderConstant[8]=<matWorldView>;
VertexShaderConstant[16]=<vecFog>;
VertexShaderConstant[32]=<vecTime>;
VertexShaderConstant[33]=(0.0f,0.5f,1.0f,2.0f); // common constants
VertexShaderConstant[34]=(-0.16161616f,0.0083333f,-0.00019841f,0.000002755731f); // (-1/3!,1/5!,-1/7!,1/9!)
VertexShaderConstant[35]=(4.0f,1.57079632f,3.14159265f,6.28318530f); // (4.0,pi/2,pi,pi*2)
VertexShaderConstant[36]=(1.07f,0.0f,0.0f,0.0f); // fixup factor
VertexShaderConstant[40]=(2.5f,1.0f,0.5f,0.1f); // wave distort x
VertexShaderConstant[41]=(5.0f,0.5f,0.25f,0.1f); // wave distort y
VertexShaderConstant[42]=(-1.0f,-0.01f,-0.04f,-0.01f); // wave distort z
VertexShaderConstant[43]=(-0.1f,-0.2f,0.1f,0.05f); // wave dir x
VertexShaderConstant[44]=(-0.005f,-0.01f,-0.005f,-0.0025f); // wave dir y
VertexShaderConstant[45]=(0.02f,0.04f,0.05f,0.1f); // wave speed
VertexShaderConstant[46]=(0.35f,0.1f,0.1f,0.025f); // lighting wave scale
VertexShaderConstant[47]=(0.6f,0.8f,0.2f,0.0f); // lighting scale bias
VertexShader=
decl
{
stream 0;
float v0[3]; //position
float v3[3]; //normal
float v7[2]; //uv
}
asm
{
vs.1.1
mov r1.w,c16.w // r1.w=1
dp4 r0,v0,c10 // distance to camera position (v0 is the position without sinusodial warping!)
add r0,r0,-c16.x // distance-fog_start
mad r0.x,-r0.x,c16.z,r1.w // 1-(distance-fog_start)*(1/(fog_end-fog_start))
max oFog.x,r0.x,c33.x // clamp with custom max value
mul r0,c43,v0.x // use vertex pos x as inputs to sinusoidal warp
mad r0,c44,v0.y,r0 // use vertex pos y as inputs to sinusoidal warp
mov r1,c32.w // get current time
mad r0,r1,c45,r0 // add scaled time
frc r0.xy,r0 // take fraction of all 4 components
frc r1.xy,r0.zwzw
mov r0.zw,r1.xyxy
mul r0,r0,c36.x // multiply by fixup factor (due to inaccuracy of taylor series)
sub r0,r0,c33.y // subtract 0.5
mul r1,r0,c35.w // range -pi to pi
mul r2,r1,r1 // wave_vec^2
mul r3,r2,r1 // wave_vec^3
mul r5,r3,r2 // wave_vec^5
mul r7,r5,r2 // wave_vec^7
mul r9,r7,r2 // wave_vec^9
mad r0,r3,c34.x,r1 // wave_vec-(wave_vec^3)/3!
mad r0,r5,c34.y,r0 // +(wave_vec^5)/5!
mad r0,r7,c34.z,r0 // -(wave_vec^7)/7!
mad r0,r9,c34.w,r0 // +(wave_vec^9)/9!
dp4 r3.x,r0,c40
dp4 r3.y,r0,c41
dp4 r3.zw,r0,c42
sub r4,c33.z,v7.y // attenuate sinusoidal warping by (1-uv.y)^2
mul r4,r4,r4
mul r3,r3,r4
mov r2.w,v0
add r2.xyz,r3,v0 // add sinusoidal warping to grass position
m4x4 oPos,r2,c0 // transform position to clip space
dp4 r1.x,r0,c46 // scale and add sin waves together
mad oD0,c47.xzxz,-r1.x,c47.y // scale and bias color values (green is scaled more than red and blue)
mov oT0.xy,v7.xy // output uvs
};
PixelShader=
asm
{
ps.1.3
def c0,1,1,1,1
def c1,0,0,0,0
tex t0 // sample t0
mov r0,t0
cnd r0.a,r0.a,c0,c1 // if(r0.a>0.5){r0.a=1;}else{r0.a=0;}
mul_x2 r0.rgb,r0,v0 // modulate with lighting
};
}
}
use some intersecting quads as grass model. the grass texture should be a tga bitmap with alphachannel. the polygons will be rendered two-sided.
there are a lot of parameters to tweak (c40-c47) and i am sure it's possible to achieve nicer motion than with my settings!
for example vertex shaders have to use taylor series to calculate sine values and i don't really understand how taylor series work! 
The only way I think they could have done it is with the method I suggest above, the grass is dense on certain parts of the course filling the rough areas perfectly, I wondered if there was a way to achieve this with your grass example? 
