2D point lights using HLSL

@AJP wrote:

I'm working on a 2D point light system for my game, and I'm passing an HLSL effect to SpriteBatch when I draw. I've got the effect working right—I think—but I'm going to run into a problem with it. The problem is, HLSL does not support dynamically sized arrays, and I want to be able to support an arbitrary number of point lights.

Here is the HLSL file:

#if OPENGL
	#define SV_POSITION POSITION
	#define VS_SHADERMODEL vs_3_0
	#define PS_SHADERMODEL ps_3_0
#else
	#define VS_SHADERMODEL vs_4_0_level_9_1
	#define PS_SHADERMODEL ps_4_0_level_9_1
#endif

texture Texture;

//Arbitrary limit of 4 lights...
float4 lights[4];

sampler TextureSampler = sampler_state{ Texture = <Texture>; };

struct VertexShaderOutput
{
	float4 Color : COLOR0;
	float2 TextureCoordinate : TEXCOORD0;
};

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
	float4 color = tex2D(TextureSampler, input.TextureCoordinate);

	//Convert the TextureCoordinate into pixel coordinates
	float2 pixelLocation = float2(1280, 720) * input.TextureCoordinate;

	//The final light level after calculations are complete
	float result = 0;

	float currentResult;

	for (int i = 0; i < lights.Length; i++)
	{
		//r and g are the x and y coordinates of the point light
		//b is the radius of the light
		//a is the opacity or brightness of the light
		currentResult = lights[i].b - distance(pixelLocation, float2(lights[i].r, lights[i].g));
		currentResult /= lights[i].b;
		currentResult *= lights[i].a;
		if (currentResult > 0) result += currentResult;
	}

	//Don't allow light level to go below .2
	if (result < .2) result = .2;

	return result * color;
}

technique Technique1
{
	pass Pass1
	{
		PixelShader = compile PS_SHADERMODEL PixelShaderFunction();
	}
}

I'm pretty new to HLSL, so I apologize if any of that code is laughably bad.

Is there any way I could use this type of point light implementation and allow for an arbitrary or dynamic amount of lights? And is there anything incorrect about the HLSL code?

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