pssm 和 vsm 到底区别在哪？

[sfkdkjjj]

pssm vsm
p 代表什么，s又代表什么?

p和s在以下这段代码中体现在哪？


// Shader global data

float4x4 viewProjection;
float4x4 world;
float3 lightDirection;
float3 lightColor;
float3 ambientColor;
float shadowMapSize;
float4x4 shadowMapMatrix;

texture shadowTexture;

sampler2D shadowMapSampler = sampler_state
{
Texture = <shadowTexture>;
MinFilter = Point;
MagFilter = Point;
MipFilter = None;
AddressU = Border;
AddressV = Border;
BorderColor = 0xFFFFFFFF;
};

texture objectTexture;

sampler2D objectTextureSampler = sampler_state
{
Texture = <objectTexture>;
MinFilter = Anisotropic;
MagFilter = Anisotropic;
MipFilter = Linear;
AddressU = Wrap;
AddressV = Wrap;
};


// --- Render Shadow Map Technique ---


void VS_RenderShadowMap(float4 pos : POSITION, out float4 outPos : POSITION, out float3 outPixelPos : TEXCOORD0)
{
float4 posWorld;

posWorld = mul(pos, world);
outPos = mul(posWorld, viewProjection);

outPixelPos = outPos.xyz;
}


float4 PS_RenderShadowMap(float3 pixelPos : TEXCOORD0): COLOR
{
// write z coordinate to texture
return pixelPos.z;
}


technique RenderShadowMap
{
pass p0
{
CullMode = CW;
VertexShader = compile vs_2_0 VS_RenderShadowMap();
PixelShader = compile ps_2_0 PS_RenderShadowMap();
}
}


// --- Render Shadowed Geometry Technique ---


void VS_Shadowed(in float4 pos : POSITION, in float3 normal : NORMAL,
float2 texCoord : TEXCOORD0,
out float4 outPos : POSITION,
out float2 outTexCoord : TEXCOORD0,
out float4 outShadowTexCoord : TEXCOORD1,
out float3 outDiffuse : COLOR0)
{
float4 posWorld;

posWorld = mul(pos, world);
outPos = mul(posWorld, viewProjection);

outDiffuse = lightColor * saturate(dot(-lightDirection, normal));

outShadowTexCoord = mul(posWorld, shadowMapMatrix);

outTexCoord = texCoord;
}


float4 PS_Shadowed(float2 texCoord : TEXCOORD0, float4 shadowTexCoord : TEXCOORD1,
float4 diffuse : COLOR0) : COLOR
{
float texelSize = 1.0f / shadowMapSize;

shadowTexCoord.xy /= shadowTexCoord.w;

float4 shadow;

shadow[0] = (shadowTexCoord.z < tex2D(shadowMapSampler, shadowTexCoord).r);
shadow[1] = (shadowTexCoord.z < tex2D(shadowMapSampler, shadowTexCoord + float2(texelSize, 0)).r);
shadow[2] = (shadowTexCoord.z < tex2D(shadowMapSampler, shadowTexCoord + float2(0, texelSize)).r);
shadow[3] = (shadowTexCoord.z < tex2D(shadowMapSampler, shadowTexCoord + float2(texelSize, texelSize)).r);

float2 lerpFactor = frac(shadowMapSize * shadowTexCoord);

float lightingFactor = lerp(lerp(shadow[0], shadow[1], lerpFactor.x),
lerp(shadow[2], shadow[3], lerpFactor.x),
lerpFactor.y);

diffuse *= lightingFactor;

float4 outColor = 1;

outColor.rgb = tex2D(objectTextureSampler, texCoord) * saturate(ambientColor + diffuse).rgb;

return outColor;
}


technique Shadowed
{
pass p0
{
CullMode = CCW;
VertexShader = compile vs_2_0 VS_Shadowed();
PixelShader = compile ps_2_0 PS_Shadowed();
}
}