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# Help! My directional light gets rotated along with my meshes :(

## 4 posts in this topic

So I have some meshes that do full rotations every say 10 seconds by rotating the model matrix an amount based on the modulus of the system clock... beginner stuff.

Great, except I have directional light coming from the sun. So I pass in sunVector to my shader, along with the vertex position and normal vector, and calculate the diffuse. Then the vertex gets MVP matrixified After the color was calculated. So it looks like the directional sunlight is rotating along with the mesh - the same side is always lit.

[source lang="java"]private final String vertexShaderCode =
"uniform mat4 u_MVPMatrix; \n"
+ "uniform mat4 u_MVMatrix; \n"
+ "uniform vec3 u_SunVector; \n"

+ "attribute vec4 a_Position; \n"
+ "attribute vec4 a_Color; \n"
+ "attribute vec3 a_Normal; \n"

+ "varying vec4 v_Color; \n"

+ "void main() \n"
+ "{ \n"

+ " vec3 modelViewNormal = vec3(u_MVMatrix * vec4(a_Normal, 0.0)); \n"

// Normalize sun vector
+ " vec3 nSunVector = normalize(u_SunVector); \n"

// Lambert factor
+ " float diffuse = max(dot(a_Normal, nSunVector), 0.0); \n"

+ " v_Color[0] = a_Color[0] * diffuse; \n"
+ " v_Color[1] = a_Color[1] * diffuse; \n"
+ " v_Color[2] = a_Color[2] * diffuse; \n"
+ " v_Color[3] = a_Color[3]; \n"
.
+ " gl_Position = u_MVPMatrix \n"
+ " * a_Position; \n"
+ "} \n"; [/source]

I must be missing a matrix somewhere?
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First I would suggest writing these in a normal text editor and reading the shader in instead of how you have it. That is pretty ghetto.

Second:
v_Color[0] = a_Color[0] * diffuse; \n"
+ " v_Color[1] = a_Color[1] * diffuse; \n"
+ " v_Color[2] = a_Color[2] * diffuse; \n"
+ " v_Color[3] = a_Color[3];

v_Color = a_Color*diffuse; //write this instead!

Third, If you are passing in the sun vector, is it changing? Try:
vec3 nSunVector = normalize(vec3(1,1,1));
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First I would suggest writing these in a normal text editor and reading the shader in instead of how you have it. That is pretty ghetto.[/quote]
Yes, I was going to be getting to that eventually. This is still just a test app / for learning.

[quote]
Second:
v_Color[0] = a_Color[0] * diffuse; \n"
+ " v_Color[1] = a_Color[1] * diffuse; \n"
+ " v_Color[2] = a_Color[2] * diffuse; \n"
+ " v_Color[3] = a_Color[3];

v_Color = a_Color*diffuse; //write this instead![/quote]
But I don't want the alpha channel attenuated. If I did it that way I'd be able to see through the meshes.

[quote]
Third, If you are passing in the sun vector, is it changing? Try:
vec3 nSunVector = normalize(vec3(1,1,1));
[/quote]
The sun vector changes very slowly over time but at the moment I'm just passing in constants for testing so it isn't that...

My problem is, I'm lighting the surfaces in world space before doing the rotations and transforming them, I know what I'm doing wrong, I just can't figure out how to do it right... Edited by Joey P
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float diffuse = max(dot(a_Normal, nSunVector), 0.0);

You have to keep both vectors in the same space. Right now your sun vector is in the world, A_Normal is static/in object space. As the model rotates, you need to take a_normal and multiply it by the model matrix. This keeps it in world space. If you put the view matrix in there as well then the normal is in view space relative to the viewer.

So multiply a_Normal by the model matrix and you are fine, or
multiply a_Normal by the modelviewmatrix and the sun by the view matrix to get them both into view space. Edited by dpadam450
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Thanks, that helped, although it's still doing some slightly goofy things... I'll just have to start stepping through code
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