Light map shader

shader.hlsl

#include "Macros.fxh"
#include "Common.fxh"

static const int MAX_LIGHTS = 50;

DECLARE_TEXTURE(Texture, 0);

uniform extern float2 LightPositions[MAX_LIGHTS];
uniform extern float4 LightColors[MAX_LIGHTS];
uniform extern float  LightRadiuses[MAX_LIGHTS];

struct VsOutput
{
	float4 PositionPS : SV_POSITION;
	float4 Color	  : COLOR0;
	float2 TexCoord   : TEXCOORD0;
};

float4 ComputeLight(float2 p)
{
	float4 light = float4(0, 0, 0, 0);
	
	int i;

	for (i = 0; i < MAX_LIGHTS; ++i)
	{
		float lightR = LightRadiuses[i];

		float4 lightC = LightColors[i];
		float2 lightP = LightPositions[i];

		float d = clamp(length(p - lightP), 0, lightR);

		float fadeCoef = lerp(1.0, 0.0, d / lightR);

		// Blending: Screen
		light = light + lightC * fadeCoef * (1 - light);
	}

	return light;
}

VsOutput LightMapVs(VsInput vin)
{
	VsOutput vout;

	vout.PositionPS = mul(vin.Position, WorldViewProj);
	vout.Color = vin.Color;
	vout.TexCoord = vin.TexCoord;

	return vout;
}

float4 LightMapPs(VsOutput pin) : SV_Target0
{
  float4 light = ComputeLight(pin.PositionPS.xy);

  return light;
}

TECHNIQUE(LightMap, LightMapVs, LightMapPs);