# OpenGL Deferred shading and point light range issue

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KaiserJohan    2317

I'm making a deferred shader and I'm having issue with point lights in that their range dosnt seem to be clamped.

When looking "through" the light volume, the entire area behind it is fully lit. The pictures below shows the problem.

I suppose there must be something I am missing when calculating the distance?

http://postimg.org/image/65ps4d6qn/

http://postimg.org/image/w7mr7a0rt/

Here is the shading pass function (depth testing is disabled aswell):

    void OpenGLRenderer::ShadingPass(const RenderableLighting& lighting)
{
GLCALL(glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT));

// activate all the gbuffer textures
GLCALL(glActiveTexture(GL_TEXTURE0 + GBuffer::GBUFFER_TEXTURE_POSITION));
GLCALL(glBindTexture(GL_TEXTURE_2D, mGBuffer.mGBufferTextures[GBuffer::GBUFFER_TEXTURE_POSITION]))
GLCALL(glGenerateMipmap(GL_TEXTURE_2D));
GLCALL(glActiveTexture(GL_TEXTURE0 + GBuffer::GBUFFER_TEXTURE_NORMAL));
GLCALL(glBindTexture(GL_TEXTURE_2D, mGBuffer.mGBufferTextures[GBuffer::GBUFFER_TEXTURE_NORMAL]));
GLCALL(glGenerateMipmap(GL_TEXTURE_2D));
GLCALL(glActiveTexture(GL_TEXTURE0 + GBuffer::GBUFFER_TEXTURE_DIFFUSE));
GLCALL(glBindTexture(GL_TEXTURE_2D, mGBuffer.mGBufferTextures[GBuffer::GBUFFER_TEXTURE_DIFFUSE]));
GLCALL(glGenerateMipmap(GL_TEXTURE_2D));

// draw fullscreen rect for ambient light

// for point lights
GLCALL(glEnable(GL_BLEND));
GLCALL(glBlendFunc(GL_ONE, GL_ONE));

// do all point lights
for (const RenderableLighting::PointLight& pointLight : lighting.mPointLights)
{
}

// reset state
GLCALL(glDisable(GL_BLEND));
GLCALL(glUseProgram(0));
}


Here is the shading pass fragment shader:

    const std::string gShadingFragmentShader =
"#version 330                                                                                                           \n \
\n \
layout(std140) uniform;                                                                                                 \n \
\n \
uniform UnifShading                                                                                                     \n \
{                                                                                                                       \n \
mat4 mWVPMatrix;                                                                                                    \n \
vec4 mLightColor;                                                                                                   \n \
vec4 mLightPosOrDir;                                                                                                \n \
vec4 mGamma;                                                                                                        \n \
vec2 mScreenSize;                                                                                                   \n \
\n \
int   mLightType;                                                                                                   \n \
float mFalloffFactor;                                                                                               \n \
float mMaxDistance;                                                                                                 \n \
} UnifShadingPass;                                                                                                      \n \
\n \
uniform sampler2D unifPositionTexture;                                                                                  \n \
uniform sampler2D unifNormalTexture;                                                                                    \n \
uniform sampler2D unifDiffuseTexture;                                                                                   \n \
\n \
out vec4 fragColor;                                                                                                     \n \
\n \
vec4 CalcPointLight(vec3 worldPos, vec3 normal)                                                                        \n \
{                                                                                                                       \n \
vec3 positionDiff = (UnifShadingPass.mLightPosOrDir.xyz - worldPos);                                                   \n \
\n \
float dist = max(length(positionDiff) - UnifShadingPass.mMaxDistance, 0);                                            \n \
\n \
float attenuation = 1 / ((dist / UnifShadingPass.mMaxDistance + 1) * (dist / UnifShadingPass.mMaxDistance + 1));  \n \
attenuation = max((attenuation - UnifShadingPass.mMaxDistance) / (1 - UnifShadingPass.mMaxDistance), 0);             \n \
\n \
vec3 lightDir = normalize(positionDiff);                                                                             \n \
float angleNormal = clamp(dot(normalize(normal), lightDir), 0, 1);                                                   \n \
\n \
return angleNormal * attenuation * UnifShadingPass.mLightColor;                                                      \n \
}                                                                                                                       \n \
\n \
vec4 CalcDirectionalLight(vec3 worldPos, vec3 normal)                                                                  \n \
{                                                                                                                       \n \
return UnifShadingPass.mLightColor;  // TODO                                                                                \n \
}                                                                                                                       \n \
\n \
vec4 CalcAmbientLight()                                                                                                 \n \
{                                                                                                                       \n \
return UnifShadingPass.mLightColor;                                                                                 \n \
}                                                                                                                       \n \
\n \
void main()                                                                                                             \n \
{                                                                                                                       \n \
vec2 texcoord = gl_FragCoord.xy / UnifShadingPass.mScreenSize;                                                      \n \
\n \
vec3 worldPos = texture(unifPositionTexture, texcoord).xyz;                                                         \n \
vec3 normal   = texture(unifNormalTexture, texcoord).xyz;                                                           \n \
vec3 diffuse  = texture(unifDiffuseTexture, texcoord).xyz;                                                          \n \
normal        = normalize(normal);                                                                                  \n \
\n \
if (UnifShadingPass.mLightType == 1)                                                                                \n \
fragColor = vec4(diffuse, 1.0) * CalcPointLight(worldPos, normal);                                              \n \
else if (UnifShadingPass.mLightType == 2)                                                                           \n \
fragColor = vec4(diffuse, 1.0) * CalcDirectionalLight(worldPos, normal);                                        \n \
else if (UnifShadingPass.mLightType == 3)                                                                           \n \
fragColor = vec4(diffuse, 1.0) * CalcAmbientLight();                                                            \n \
else                                                                                                                \n \
fragColor = vec4(diffuse, 0.0);                                                                                 \n \
}                                                                                                                       \n";

Edited by KaiserJohan

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RnaodmBiT    1096

It is because you are calculating your light strength at each pixel as 1/r^2 which is physically correct, but when using point light volumes as you are results in the shown issue, There are two options:

1) Change the light strength to being 1 - dis / maxDis which will give you a linear light strength to the edge of the lights 'radius' but isn't physically correct

2) You can change the light volume from being a sphere at the lights position to being a fullscreen quad. This essentially will calculate the light strenght for ALL pixels which is physically accurate since light strength is an inverse squared relationship (1/r^2). Since 1/r^2 will never actually be 0 then your point light will have even a tiny effect on pixels extremely far away and a large effect on very close pixels.

I hope that explains your issue.

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Hodgman    51336

You can also modify the distance-squared attenuation and force it to reach zero at some point:

atten = 1/(d^2)
threshold = 0.1
newAtten = saturate( (atten-threshold)/(1-threshold) )

Maximum shading radius is where newAtten == 0, or where atten == threshold

e.g.

0.1 == 1/(d^2), solve for d

d = 3.16228

 After actually looking at your code, you're already doing something like this

Can you explain the theory behind your attenuation formula and the use of the maxDistance parameter?

Edited by Hodgman

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KaiserJohan    2317

I'd rather go for 1);

Here's what I got then

http://postimg.org/image/xtld8cevz/  -  you can see the bounding sphere not touching the chair

http://postimg.org/image/q087316yb/   - it actually lits the chair

With the small change to calculate attenuation:

    vec4 CalcPointLight(vec3 worldPos, vec3 normal)                                                                        \n \
{                                                                                                                       \n \
vec3 positionDiff = (UnifShadingPass.mLightPosOrDir.xyz - worldPos);                                                   \n \
\n \
float dist = max(length(positionDiff) - UnifShadingPass.mMaxDistance, 0);                                            \n \
\n \
//float attenuation = 1 / ((dist / UnifShadingPass.mMaxDistance + 1) * (dist / UnifShadingPass.mMaxDistance + 1));  \n \
//attenuation = max((attenuation - UnifShadingPass.mMaxDistance) / (1 - UnifShadingPass.mMaxDistance), 0);             \n \
float attenuation = 1.0 - (dist / UnifShadingPass.mMaxDistance);                                                                                                                   \n \
vec3 lightDir = normalize(positionDiff);                                                                             \n \
float angleNormal = clamp(dot(normalize(normal), lightDir), 0, 1);                                                   \n \
\n \
return angleNormal * attenuation * UnifShadingPass.mLightColor;                                                      \n \
}                                                                                                                       \n \


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KaiserJohan    2317

My idea with max distance is to have it be 0 at maxDistance and 1 at the centre, so it clamps between the two. Then to have an additional parameter, what I call "FalloffFactor" to be how steep the falloff is between 1 and maxdistance

At the moment I'm ready to accept the simplest just to get the actual light volume working properly before trying a better formula, as shown it dosnt work properly in the pcitures in the previous post - something is bollocks and I dont know what

The light spheres radius is the maxdistance btw

Edited by KaiserJohan

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RnaodmBiT    1096
 vec4 CalcPointLight(vec3 worldPos, vec3 normal)                                                                        \n \
{                                                                                                                       \n \
vec3 positionDiff = (UnifShadingPass.mLightPosOrDir.xyz - worldPos);                                                   \n \
\n \
float dist = length(positionDiff);                                            \n \
\n \
float attenuation = clamp(1.0 - (dist / UnifShadingPass.mMaxDistance), 0.0, 1.0);                                                                                                                   \n \
vec3 lightDir = normalize(positionDiff);                                                                             \n \
float angleNormal = clamp(dot(normalize(normal), lightDir), 0, 1);                                                   \n \
\n \
return angleNormal * attenuation * UnifShadingPass.mLightColor;                                                      \n \
} 

That *should* do it, note how the formula is a little different, also the clamp will tidy things up a little bit. As for your falloff you will need to form some kind off function to get you a desired curve.

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KaiserJohan    2317

Thanks, it works wonderfull!

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