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Shading changes when camera moves


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#1 rocklobster   Members   -  Reputation: 415

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Posted 03 December 2012 - 02:27 AM

Hi guys,

I've got this problem where the shading of my objects changes when my camera moves. The obvious solution is that I'm not transforming my light into eye space before sending it to the shader, but I am doing this. Another thing to note is that when I leave my light AND normals in world space, it works fine.


glm::mat4 modelView = m_camera->GetView() * glm::mat4(1.0);

m_graphics->SetUniform(id, "u_ModelViewMatrix", 1, false, modelView);
m_graphics->SetUniform(id, "u_NormalMatrix", 1, false, glm::mat3(glm::vec3(modelView[0]), glm::vec3(modelView[1]), glm::vec3(modelView[2])));
m_graphics->SetUniform(id, "u_MVP", 1, false, m_graphics->GetProjMatrix() * modelView);

m_graphics->SetUniform(id, "Light.Position", modelView * glm::vec4(-100.0f, 50.0f, 30.0f, 1.0f));

This is how I'm calculating my view matrix

void ViewFrustum::Update()
{
  m_direction = glm::vec3(cos(m_yaw) * sin(m_pitch),
			  sin(m_yaw),
			  cos(m_yaw) * cos(m_pitch));
  m_view = glm::lookAt(m_position, m_position + m_direction, glm::vec3(0, 1, 0));
  m_right = glm::cross(m_up, m_direction);
}

The camera works fine and I move around the world with no troubles.

Here's my shader code. It's actually just storing the values in a GBuffer for deferred rendering.

Vertex
#version 400

layout (location = 0) in vec3 in_Position;
layout (location = 1) in vec3 in_Normal;
layout (location = 2) in vec3 in_TexCoord;

out vec3 Position;
out vec3 Normal;
out vec3 TexCoord;

uniform mat4 u_ModelViewMatrix;
uniform mat3 u_NormalMatrix;
uniform mat4 u_MVP;

void main()
{
	Position = in_Position;
	Normal =  normalize(u_NormalMatrix * in_Normal);
	TexCoord = in_TexCoord;

	gl_Position = u_MVP * vec4(Position, 1.0);
}

In the second pass I use the Light.Position variable:

vec3 shadePixel(vec3 pos, vec3 norm, vec3 diff)
{
	if (diff == vec3(1.0, 1.0, 1.0)) return vec3(1.0, 1.0, 1.0);

	vec3 s = normalize(vec3(Light.Position) - pos);
	float sDotN = max(dot(s, norm), 0.0);
	vec3 diffuse = Light.Intensity * diff * sDotN;

	return diffuse;
}
// get the values from GBuffer
vec4 diffusePass()
{
    vec3 pos = vec3(texture2D(positionTexture, UV));
    vec3 norm = vec3(texture2D(normalTexture, UV));
    vec3 diff = vec3(texture2D(diffuseTexture, UV));

    return vec4(shadePixel(pos, norm, diff), 1.0);
}

If I don't multiply the normal by u_NormalMatrix and I don't multiply the light position by the view matrix it works fine. Can't spot why it wont work in view space.

Thanks for the help in advance.

Edited by rocklobster, 03 December 2012 - 08:46 AM.


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#2 Auskennfuchs   Members   -  Reputation: 553

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Posted 03 December 2012 - 11:40 AM

The MVP-Matrix consists of 3 components:
1. Modelmatrix is the scaling, rotation and translation of the object
2. Viewmatrix is the position, lookat, rotation of the camera
3. Projectionmatrix is the "presentation to the 2d screen"

Seems like you use the model*view-matrix for your normalmatrix. Try to use just the modelmatrix for transforming the normal in your shader.
The position of object and light is independent from the position of the camera.

#3 rocklobster   Members   -  Reputation: 415

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Posted 03 December 2012 - 12:40 PM

http://www.lighthouse3d.com/tutorials/glsl-tutorial/the-normal-matrix/

This link explains pretty well why I'm using the view matrix to do lighting calculations. I don't want to do the calculations in world/model space.

#4 L. Spiro   Crossbones+   -  Reputation: 12873

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Posted 03 December 2012 - 07:20 PM

Render the normals to the final color buffer instead of the diffuse so that you can see the actual normal X, Y, and Z values.
As you rotate the camera, each surface of each object should change color. Floors should be green if you are looking straight, but turn black if you look down.
If they do not, the problem is in your normal matrix (which should be the inverse-transpose of the model-view matrix, not just the model-view matrix).

If they do look fine, the problem is in your light direction.


L. Spiro

Edited by L. Spiro, 04 December 2012 - 01:08 AM.

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#5 rocklobster   Members   -  Reputation: 415

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Posted 03 December 2012 - 10:38 PM

Render the normals to the final color buffer instead of the diffuse so that you can see the actual normal X, Y, and X values.
As you rotate the camera, each surface of each object should change color. Floors should be green if you are looking straight, but turn black if you look down.
If they do not, the problem is in your normal matrix (which should be the inverse-transpose of the model-view matrix, not just the model-view matrix).

If they do look fine, the problem is in your light direction.


L. Spiro


The floor was green when the camera is in normal position, as I pitch down the floor fades from green -> teal -> blue. That shouldn't be right? Blue would mean (0, 0, 1) normal value which isn't correct. I tried putting a glm::inverse() around my normal matrix but had the same results.

#6 L. Spiro   Crossbones+   -  Reputation: 12873

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Posted 04 December 2012 - 01:08 AM

Actually that is correct. Green to blue.
And the normal matrix is modelView.Transpose().Inverse(), not modelView.Inverse().

It means your light’s position is wrong. The light’s position should be transformed by the view.Inverse() matrix, not the modelView matrix.


L. Spiro

Edited by L. Spiro, 04 December 2012 - 01:16 AM.

It is amazing how often people try to be unique, and yet they are always trying to make others be like them. - L. Spiro 2011
I spent most of my life learning the courage it takes to go out and get what I want. Now that I have it, I am not sure exactly what it is that I want. - L. Spiro 2013
I went to my local Subway once to find some guy yelling at the staff. When someone finally came to take my order and asked, “May I help you?”, I replied, “Yeah, I’ll have one asshole to go.”
L. Spiro Engine: http://lspiroengine.com
L. Spiro Engine Forums: http://lspiroengine.com/forums

#7 rocklobster   Members   -  Reputation: 415

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Posted 04 December 2012 - 02:17 AM

Ok I've changed my normal matrix to

m_graphics->SetUniform(id, "u_NormalMatrix", 1, false,
	glm::inverse(glm::transpose(glm::mat3(glm::vec3(viewMatrix[0]), g	lm::vec3(viewMatrix[1]), glm::vec3(viewMatrix[2])))));

and the light is

glm::vec4 lightPosViewSpace = glm::inverse(g->GetViewMatrix()) * glm::vec4(-50.0f, 150.0f, 30.0f, 1.0f);
g->SetUniform(id, "Light.Position", lightPosViewSpace);

Perhaps I should multiply the position in my frag shader by model view matrix such as:

vec3 s = normalize(vec3(Light.Position) - (u_ModelViewMatrix * vec4(pos, 1.0)));

Because I'm just passing it through my geom buffer shader unchanged:

Position = in_Position;

EDIT: The shading still changes when the camera moves. If I turn around from origin in the scene and start tilting down, the floor and everything just turns black. And actually i think putting the inverse after the transpose didn't actually change a thing.

Edited by rocklobster, 04 December 2012 - 02:38 AM.


#8 L. Spiro   Crossbones+   -  Reputation: 12873

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Posted 04 December 2012 - 08:25 AM

It won’t change anything unless you have non-uniform scaling in either the world matrix or the view matrix.


Also I might have mislead you in my previous post. I meant to say the inverse of the camera matrix, which is in itself the view matrix, so rather than taking the inverse of the view matrix it should be just the view matrix. It was minutes before I passed out of sheer sleepiness and I wasn’t thinking straight.

It should likely fix your problem to multiply the light position by the raw view matrix.


L. Spiro
It is amazing how often people try to be unique, and yet they are always trying to make others be like them. - L. Spiro 2011
I spent most of my life learning the courage it takes to go out and get what I want. Now that I have it, I am not sure exactly what it is that I want. - L. Spiro 2013
I went to my local Subway once to find some guy yelling at the staff. When someone finally came to take my order and asked, “May I help you?”, I replied, “Yeah, I’ll have one asshole to go.”
L. Spiro Engine: http://lspiroengine.com
L. Spiro Engine Forums: http://lspiroengine.com/forums

#9 rocklobster   Members   -  Reputation: 415

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Posted 04 December 2012 - 09:11 AM

No problem, I often do too much coding whilst half asleep :P

So I've multiplied the light position by just the view matrix and the floor doesn't change to black any more when I rotate and look down. The other objects still seem to shade differently when I translate and rotate around the world. I'm still kind of confused because when I leave the normal/light in world space the shading is all static no matter where I move, but as soon as I multiply the normals and the light by the normal/view matrix the shading changes based on my camera (this sounds like it is expected, but I never see this in games anywhere?). I'm not multiplying the position by the modelview matrix before sending it to the Geom Buffer, which is ok because if i do the world looks and behaves weirdly. But even if I multiply the position by the modelview matrix in the frag shader just to calculate the direction of the light to that position in the texture it seems to be have the same way.




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