Passing structs to shaders

[3DModelerMan]

I have an HLSL struct that looks like this:

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struct Light
{
float4 DiffuseColor;
 
float4 SpecularColor;
 
float4 AmbientColor;
 
float4 Attenuation;
 
float OuterCone;
 
float InnerCone;
 
float Falloff;
        
float4 Position;
 
float4 Direction;
 
float Radius;
 
int LightType;
};
 

I also defined light types and a light array in the shader:

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#define MaxLights 8 
 
static int POINT = 0;
static int SPOT = 1;
static int DIRECTIONAL = 2;
 
Light lights[MaxLights];
 

I'm trying to pass this C++ struct to HLSL:

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struct Light
{
        irr::video::SColorf DiffuseColor;
 
        irr::video::SColorf SpecularColor;
 
        irr::video::SColorf AmbientColor;
 
        irr::core::vector3df Attenuation;
        float pad0;
 
        float OuterCone;
 
        float InnerCone;
 
        float Falloff;
 
        irr::core::vector3df Position;
        float pad1;
 
        irr::core::vector3df Direction;
        float pad2;
 
        float Radius;
 
        irr::u32 LightType;
};
 

I didn't decide to use the Irrlicht SLight structure because it doesn't have padding. This is how I pass the data to the shader:

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if ( UseLights && MaxLights > 0 )
        {
                irr::u32 numLights = driver->getDynamicLightCount();
 
                for (irr::u32 i=0; i<numLights; ++i)
                {
                        if ( i > MaxLights )
                                break;
 
                        //Light structure to be passed to shader
                        Light light;
                        //Irrlicht light structure (can't be directly passed because it contains no padding).
                        irr::video::SLight irrLight = driver->getDynamicLight(i);
 
                        //Copy to the padded light struct
                        light.DiffuseColor = irrLight.DiffuseColor;
                        light.SpecularColor = irrLight.SpecularColor;
                        light.AmbientColor = irrLight.AmbientColor;
                        light.Attenuation = irrLight.Attenuation;
                        light.OuterCone = irrLight.OuterCone;
                        light.InnerCone = irrLight.InnerCone;
                        light.Falloff = irrLight.Falloff;
                        light.Position = irrLight.Position;
                        light.Direction = irrLight.Direction;
                        light.Radius = irrLight.Radius;
                        light.LightType = (irr::u32)irrLight.Type;
 
                        services->setPixelShaderConstant("lights", reinterpret_cast<irr::f32*>(&light), 1);
                }
        }
 

Any idea what's wrong with it? I've never passed structs before, so I don't know if I'm supposed to be passing them in a loop or if there's a different way.

[3DModelerMan]

Do I even need padding?

[Klunk]

I've no idea if that would work but shouldn't the 1 in setPixelShaderConstant be sizeof(Light)/4 ?

[3DModelerMan]

Oh yeah. It's the number of floats to set, not the number of variables. I forgot that part. I'll change my code when I get a chance and post back if it works.

[Mel]

Make sure that the size of each structure matches in both places. Shaders get mainly floats, And irrlichts passes floats in the constant set callbacks. (the last parameter of the constants set methods is a float*) So, technically, you can't pass integers. But that's an issue that probably can be solved if you cast the light structure address to a float*, and the size of the light structure is a multiple of the size of a float.

[3DModelerMan]

I tried and it still wouldn't work. I even tried just setting a single struct instead of an array of them:

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//Light structure to be passed to shader
                Light light;
                //Irrlicht light structure (can't be directly passed because it contains no padding).
                irr::video::SLight irrLight = driver->getDynamicLight(0);
 
                //Copy to the padded light struct
                light.DiffuseColor = irrLight.DiffuseColor;
                light.SpecularColor = irrLight.SpecularColor;
                light.AmbientColor = irrLight.AmbientColor;
                light.Attenuation = irrLight.Attenuation;
                light.OuterCone = irrLight.OuterCone;
                light.InnerCone = irrLight.InnerCone;
                light.Falloff = irrLight.Falloff;
                light.Position = irrLight.Position;
                light.Direction = irrLight.Direction;
                light.Radius = irrLight.Radius;
                light.LightType = (irr::u32)irrLight.Type;
 
                services->setPixelShaderConstant("light", reinterpret_cast<irr::f32*>(&light), (sizeof(Light)/4));
 

And the shader now has this instead of a loop:

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output.Diffuse.rgb = light.DiffuseColor;
output.Diffuse.a = 1.0f;
 

[Mel]

And it still doesn work?... Well, shaders can be very tight in some matters. For instance, 4x4 matrices become 3x3 matrices when the shaders get compiled if you only use 3 components in a vector, and stuff like that. Maybe a struct can't be optimized the same, because of the potential waste of space if a variable is unused within a structure. But i can't tell for sure.

[docWild]

I used to use structs all the time in C but I have no luck in using them for C++. I can't see what you're doing wrong, but what I generally do these days is use a class with public methods/attributes instead. The only real difference being that class objects are always passed by reference.

[aanderse]

what is the sizeof (Light) ?

[Radikalizm]

I've had some issues with passing structs to hlsl shaders in the past having to do with alignment (which went beyond the simple 4 byte alignment)
DX warned me though when I tried to pass a non-aligned structure though when running a debug build and informed me about the expected size. Maybe try to run a debug build of irrlicht to see whether DX gets more verbose?

I was using DX10 though back then, don't know if it will make a difference with DX9

[serengeor]

what is the sizeof (Light) ?

I might have misunderstood your question. I think it's the size of struct/class Light, as sizeof(..) returns size in bytes.

[aanderse]

yes sorry i wasn't clear
i meant what is the actual size of that struct for 3DModelerMan on his compiler/computer setup
i just wanted to confirm the actual size of the struct (in bytes, as you mentioned) isn't funky/unexpected due to hidden compiler padding, etc...