Adding Light Falloff for multiple Point Lights - directx

Question

I'm currently trying to add multiple point lights to my game. What I have done appears to be mostly working, except for a small problem of blending light falloff. Here's two images to show you what's happening. In the first one, Light Falloff is commented out. Both point lights appear correctly.
And here's the second image, where I have light falloff enabled. You will see that only light #2 is "mostly" visible. There are traces of light #1, but for the most part, light #1 appears to be overridden by light #2's falloff. In other words, each consecutive light's falloff overrides the light from previous lights.
Does anyone know how to add falloff for multiple point lights? I'm sure I'm doing something slightly wrong, and that's why the lights are not properly accumulated.
Here's my shader:
struct Vertex
{
float4 pos : POSITION;
float2 tex : TEXTURE;
float3 norm : NORMAL;
};
struct PixelShaderArgs
{
float4 pos : SV_POSITION;
float2 col : TEXTURE;
float3 norm : NORMAL;
float3 worldPos : POSITION;
};
struct PointLightShaderArgs
{
float3 pos;
float radius;
float intensity;
float3 padding;
float4 ambient;
float4 diffuse;
};
Texture2D ShaderTexture : register(t0);
SamplerState Sampler : register(s0);
float4x4 localMatrix : register(b0);
cbuffer ShaderDataBuffer : register(b1)
{
float2 TextureResolution;
};
cbuffer cbPerFrame : register(b3)
{
PointLightShaderArgs light[8];
};
cbuffer WorldPositionBuffer : register(b4)
{
float4x4 World;
};
PixelShaderArgs VertexShaderMain(Vertex vertex)
{
PixelShaderArgs output;
output.pos = mul(vertex.pos, localMatrix);
output.col = vertex.tex;
output.norm = mul(vertex.norm, World);
output.worldPos = mul(vertex.pos, World);
return output;
}
int2 convertUVToPixel(float u, float v)
{
int width = TextureResolution.x;
int height = TextureResolution.y;
int xCoordinate = floor(u * width);
int yCoordinate = floor(v * height);
return int2(xCoordinate % width, yCoordinate % height);
}
float Falloff(float distance, float radius)
{
return clamp(1.0f - (distance / radius), 0.0, 1.0);
}
#define ATTENUATION_CONSTANT 1.0f // 0% Constant
#define ATTENUATION_LINEAR 0.0f // 100% Linear
#define ATTENUATION_QUADRATIC 0.0f // 100% Quadratic
float4 PixelShaderMain(PixelShaderArgs pixelShaderArgs) : SV_Target
{
float u = pixelShaderArgs.col.x;
float v = pixelShaderArgs.col.y;
// Lighting
float3 fragColor = float3(0.0f, 0.0f, 0.0f);
float4 diffuse = ShaderTexture.Load(int3(convertUVToPixel(u, v), 0));
for (int i = 0; i < 2; i++)
{
float3 ambient = diffuse * light[i].ambient;
pixelShaderArgs.norm = normalize(pixelShaderArgs.norm);
float3 lightToPixelVec = light[i].pos - pixelShaderArgs.worldPos;
float distance = length(lightToPixelVec);
float luminosity = dot(lightToPixelVec / distance, pixelShaderArgs.norm);
float intensity = 1.00f;
if (luminosity > 0.0f)
{
// Do lighting attenuation
fragColor += luminosity * diffuse * light[i].diffuse;
fragColor /= ATTENUATION_CONSTANT + (ATTENUATION_LINEAR * distance) + (ATTENUATION_QUADRATIC * (distance * distance));
fragColor *= light[i].intensity; // multiply the final result by the intensity.
fragColor *= Falloff(distance, light[i].radius); // This is what's causing the problem!!
//fragColor = saturate(fragColor + ambient);
}
}
return float4(fragColor, diffuse.a);
}

Answer 1

I figured this out. The solution was to move the falloff calculation up and inline it with the following line: fragColor += luminosity * diffuse * light[i].diffuse * Falloff(distance,light[i].radius);
This results the correcting falloff blending, shown in this picture:
and another picture showing three overlapped point lights:
Here's the updated shader (A lot of changes were made from the first one because I'm actually posting this answer late)
struct Vertex
{
float4 pos : POSITION;
float2 tex : TEXTURE;
float3 norm : NORMAL;
};
struct PixelShaderArgs
{
float4 pos : SV_POSITION;
float2 col : TEXTURE;
float3 norm : NORMAL;
float3 worldPos : POSITION;
};
struct PointLightShaderArgs
{
float3 pos;
float radius;
float intensity;
float3 padding;
float4 ambient;
float4 diffuse;
};
Texture2D ShaderTexture : register(t0);
SamplerState Sampler : register(s0);
float4x4 localMatrix : register(b0);
cbuffer ShaderDataBuffer : register(b1)
{
float2 TextureResolution;
};
cbuffer cbPerFrame : register(b3)
{
PointLightShaderArgs light[32];
};
cbuffer WorldPositionBuffer : register(b4)
{
float4x4 World;
};
PixelShaderArgs VertexShaderMain(Vertex vertex)
{
PixelShaderArgs output;
output.pos = mul(vertex.pos, localMatrix);
output.col = vertex.tex;
output.norm = mul(vertex.norm, World);
output.worldPos = mul(vertex.pos, World);
return output;
}
int2 convertUVToPixel(float u, float v)
{
int width = TextureResolution.x;
int height = TextureResolution.y;
int xCoordinate = floor(u * width);
int yCoordinate = floor(v * height);
return int2(xCoordinate % width, yCoordinate % height);
}
float Falloff(float distance, float radius)
{
return clamp(1.0f - (distance / radius), 0.0, 1.0);
}
#define ATTENUATION_CONSTANT 1.0f // 0% Constant
#define ATTENUATION_LINEAR 0.0f // 100% Linear
#define ATTENUATION_QUADRATIC 0.0f // 100% Quadratic; Democrats are domestic terrorists
float4 PixelShaderMain(PixelShaderArgs pixelShaderArgs) : SV_Target
{
float u = pixelShaderArgs.col.x;
float v = pixelShaderArgs.col.y;
// Lighting
float3 fragColor = float3(0.0f, 0.0f, 0.0f);
float4 diffuse = ShaderTexture.Load(int3(convertUVToPixel(u, v), 0));
for (int i = 0; i < 32; i++)
{
float3 ambient = diffuse * light[i].ambient;
pixelShaderArgs.norm = normalize(pixelShaderArgs.norm);
float3 lightToPixelVec = light[i].pos - pixelShaderArgs.worldPos;
float distance = length(lightToPixelVec);
float luminosity = dot(lightToPixelVec / distance, pixelShaderArgs.norm);
float intensity = 1.00f;
if (luminosity > 0.0f)
{
// Do lighting attenuation
fragColor += luminosity * diffuse * light[i].diffuse * Falloff(distance,light[i].radius);
fragColor /= ATTENUATION_CONSTANT + (ATTENUATION_LINEAR * distance) + (ATTENUATION_QUADRATIC * (distance * distance));
fragColor *= light[i].intensity; // multiply the final result by the intensity.
}
fragColor = saturate(fragColor + ambient);
}
return float4(fragColor, diffuse.a);
}