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anders211

shader vertex inputs calculations

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I know that in vertex shader 2.0 and 3.0 there might be max 256 inputs (each float4 type). So we might introduce 4x256=1024 float data into vertex shader. I have two questions?

1.) How much texture input use float data?

2.) I am able to allocate 1039 floats, please see below my calculations and I don't see anything wrong in my application. However when I add one float4 more  (introduce matrix F[61] insetad of F[60]) then I see that it doesn't work as expected.

So maybe there are max 260 (1040 floats) vertex shader registers not 256???

 

My vertex shader inputs:

uniform extern float4x4 MatWorld;  //16 floats
uniform extern float4x4 MatWorldInvTrans;  //32 floats use till now
uniform extern float4x4 MatWVP; //48 floats use till now
uniform extern float4x4 F[60]; //60*4*4+12 = 960+48=1008 floats use till now
uniform extern float3 toCam; //1011

struct Mtrl
{
float4 Ambient; //1015
float4 Diffuse; //1019
float4 Specular; //1023
float Power; //1024
};
struct LightStr
{
float4 Ambient; //1028
float4 Diffuse; //1032
float4 Specular; //1036
float3 Direction; //1039
};

uniform extern Mtrl mtrl;
uniform extern LightStr lightStr;

uniform extern texture textura; //probably also uses some data however I don't know how much
sampler Sampl = sampler_state
{
Texture = <textura>;
MinFilter = LINEAR;
MagFilter = LINEAR;
MipFilter = LINEAR;
AddressU = WRAP;
AddressV = WRAP;
};

...

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Haven't done DX9 in years, but -

256 is the minimum requirements. You can call GetCaps() and check the value of MaxVertexShaderConst to get the actual number of registers your GPU supports.

 

Also note that there are some alignment issues. LightStr::Direction will actually take space of 4 floats, as well as Mtrl::Power - each register is 4 floats, regardless of the actual data type used. You need to count registers, not floats.

 

Textures do not consume CB registers, they have their own register-set.

 

[EDIT] - This is the SM4.0 HLSL constant buffer packing rules. I see no reason why DX9 HLSL packing rules should be different.

Edited by N.I.B.

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The DX9 rules for packing are the same, the runtime will try to pack all it can into a single float4 but it will not be smart about this, if the constant doesn't fit in the previous float4 it will start a new one. This is why you often stuff certain data in the w component of other vectors when they arent needed.

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