Weird white outline around model

Question

I'm working on a game in XNA 4 and I recently switched to a deferred shading implementation following this guide. A strange white outline is showing up on my models now and I'm not sure whats causing this. I thought maybe it was a lack of precision on the normal render target or the depth render target but increasing them to 64 bits (Rgba64) instead of 32 (Color) didn't help. I also thought it might be some problem with the specular calculation so I tried setting the specular to 0 but that didn't help either. Debugging the pixel in PIX shows the diffuse value is being calculated as nearly white for that pixel. Any ideas? I included a picture of the problem below, it's easier to see it at full size.

Pixel Shader:

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
    input.ScreenPosition.xy /= input.ScreenPosition.w;

    float2 texCoord = 0.5f * (float2(input.ScreenPosition.x, -input.ScreenPosition.y) + 1) - halfPixel;

    float4 normalData = tex2D(normalSampler, texCoord);

    //Transform normal back into [-1, 1] range
    float3 normal = normalize(2.0f * normalData.xyz - 1.0f);

    float specularPower = normalData.a;
    float specularHardness = tex2D(colorSampler, texCoord).a * 255;
    float depthVal = tex2D(depthSampler, texCoord).r;

    //Compute screen-space position
    float4 position = float4(input.ScreenPosition.xy, depthVal, 1.0f);

    //Transform to world space
    position = mul(position, InvertViewProjection);
    position /= position.w;

    //Surface-to-light vector
    float3 lightVector = lightPosition - position;

    float3 projectedTexCoords = position - lightPosition;
    projectedTexCoords = mul(projectedTexCoords, float3x3(
                            float3(-1, 0, 0),
                            float3(0, 1, 0),
                            float3(0, 0, 1)));

    float distanceToLight = length(lightVector) / lightRadius;
    float shadow = ShadowContribution(projectedTexCoords, distanceToLight);

    float attenuation = saturate(1.0f - distanceToLight);

    lightVector = normalize(lightVector);

    //Compute diffuse light
    float normalDotLight = max(0, dot(normal, lightVector));
    float3 diffuseLight = normalDotLight * Color.rgb;

    float3 reflectionVector = normalize(reflect(-lightVector, normal));
    float3 directionToCamera = normalize(cameraPosition - position);
    float specularLight = specularPower * pow(saturate(dot(reflectionVector, directionToCamera)), specularHardness);

    return shadow * attenuation * lightIntensity * float4(diffuseLight.rgb, specularLight);
}

Edit: Sorry about the JPG, stackexchange's uploader did that on its own. Roy T: I did actually reference your XNA4 conversion of the tutorial for the parts that changed from XNA3. Since I didn't make any big changes to the code I thought maybe this bug existed in the original but was just impossible to see with so many lights all moving around, so I removed all but one light and the bug showed up again (look near the lizard's elbow)

Here are the GBuffer contents for my scene:

Color Buffer: Depth Buffer: Normal Buffer: Final Render:

Edit2:

I'm starting to suspect the problem is CombineFinal.fx when it samples the color map. This is the computation for a properly colored pixel right next to a white pixel:

diffuseColor        : (0.435, 0.447, 0.412)
diffuseLight        : (1.000, 1.000, 0.902)
light               : (1.000, 1.000, 0.902, 0.000)
PixelShaderFunction : (0.435, 0.447, 0.371, 1.000)
specularLight       : 0.000

And this is the output from an improperly colored white pixel directly next to it:

diffuseColor        : (0.824, 0.792, 0.741)
diffuseLight        : (1.000, 1.000, 0.902)
light               : (1.000, 1.000, 0.902, 0.000)
PixelShaderFunction : (0.824, 0.792, 0.669, 1.000)
specularLight       : 0.000

The diffuseColor is the only difference, and this color is taken directly from the color map. Perhaps there is a slight error in the computation of the texture coordinate to sample from?

Lighting Pass:

Answer 1

I had this white outline or "halo" around my models too, when I started on my own deferred renderer. The problem was that the texture offset value for overlaying the render targets was not setup correctly. Some textures needed to be set to +0.5 pixels for the offset instead of -0.5 pixels.

It was only after tweaking values of some of the texture offsets that the outlines were gone. Most likely it's in one of the lighting shaders.

Edit: by the way I also learned from Catalin Zima's tutorial which is a branch off of your example, so it should work.

Answer 2

I'm not sure exactly what's going on, but a couple of things to double-check:

1. Make sure you've got texture filtering turned off when sampling the G-buffers - no bilinear or anisotropic or anything.

2. I see you're adding a half-pixel offset to the texture coordinates; double-check that that's right. I'm not familiar enough with XNA to know what the right offset should be, but you should be able to check it by writing a shader that samples one of the G-buffers and just outputs the sample. Then flip back and forth between this and displaying the G-buffer directly on-screen. If you've got the correct offset, you should see no differences, not even a single pixel.