I am having a slight problem with my Bump Mapping project. Although everything works OK (at least from what I know) there is a slight mistake somewhere and I get incorrect shading on the brick wall when the light goes to the one side or the other as seen in the picture below:

enter image description here

The light is on the right side so the shading on the wall should be the other way. I have provided the shaders to help find the issue (I do not have much experience with shaders).


varying vec3 viewVec;
varying vec3 position;
varying vec3 lightvec;
attribute vec3 tangent; 
attribute vec3 binormal;
uniform vec3 lightpos;
uniform mat4 cameraMat;

void main()

    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_Position = ftransform();

    position = vec3(gl_ModelViewMatrix * gl_Vertex);
    lightvec = vec3(cameraMat * vec4(lightpos,1.0)) - position ;

    vec3 eyeVec = vec3(gl_ModelViewMatrix * gl_Vertex);
    viewVec = normalize(-eyeVec);


uniform sampler2D colormap;
uniform sampler2D normalmap;

varying vec3 viewVec;
varying vec3 position;
varying vec3 lightvec;

vec3 vv;

uniform float diffuset;
uniform float specularterm;
uniform float ambientterm;

void main() {


    vec3 normals = normalize(texture2D(normalmap,gl_TexCoord[0].st).rgb * 2.0 - 1.0);

    normals.y = -normals.y;

    //normals = (normals * gl_NormalMatrix).xyz ;

    vec3  distance = lightvec;
    float dist_number =length(distance);
    float final_dist_number = 2.0/pow(dist_number,diffuset);
    vec3  light_dir=normalize(lightvec);
    vec3  Halfvector = normalize(light_dir+vv);
    float angle=max(dot(Halfvector,normals),0.0);
          angle= pow(angle,specularterm);
    vec3 specular=vec3(angle,angle,angle);
    float diffuseterm=max(dot(light_dir,normals),0.0);
    vec3 diffuse = diffuseterm * texture2D(colormap,gl_TexCoord[0].st).rgb;
    vec3 ambient = ambientterm *texture2D(colormap,gl_TexCoord[0].st).rgb;
    vec3 diffusefinal = diffuse * final_dist_number;
    vec3 finalcolor=diffusefinal+specular+ambient;

    gl_FragColor = vec4(finalcolor, 1.0);

  • \$\begingroup\$ well I would suspect your cameraMat having wrong values. You are also flipping you normals y why is that ? \$\endgroup\$
    – concept3d
    Oct 8, 2013 at 21:58
  • 1
    \$\begingroup\$ This is not bump mapping, it is normal mapping. You will need to calculate a "tangent space to object space" transformation per vertex, you can handle right or left handed bumpmaps through that too. \$\endgroup\$
    – MickLH
    Nov 10, 2013 at 8:10

1 Answer 1


I am flipping y because the bricks were lit on the opposite side, and that fixed it.

I found the problem with the shadow: I had to do position = cameraMAT *gl_Vertex instead of gl_Modelviewmatrixi.

I do not really know why this fixed the problem though.


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