GLSL点光源转换

Question

I wrote a basic vertex shader in GLSL. Here is the source code:

varying float intensity;
uniform vec4 lightPos;

void main() {
    intensity = 0.1;
    vec3 tfVert = (gl_ModelViewMatrix*gl_Vertex).xyz;
    vec3 tfNorm = normalize(gl_NormalMatrix*gl_Normal).xyz;
    vec3 tfLightPos = (gl_ModelViewMatrix*lightPos).xyz;

    vec3 lightDir = normalize(tfLightPos-tfVert).xyz;
    intensity += dot(lightDir, tfNorm);

    gl_Position = gl_ModelViewProjectionMatrix*gl_Vertex;
}

After that, the fragment shader lights the fragment with a brightness of the varying intensity float. Here's what goes wrong: I draw a few cubes, and load an OBJ model into the world, or something like that. Then I use glRotatef() and glTranslatef() and draw the same stuff again. The light shows up twice, (sort of) at two different locations. Once at the translated position and once at the original position. The translated model is only affected by the light in the translated position, and the original model is only affected by the light in the original position. Also, it is crucial that I do not use gl_LightSource0[] to fix this problem. Is there something I am doing wrong? Is there any way to fix this? I am using glTranslatef() and glRotatef() for camera positioning and rotation, if that matters.

Answer 1

Don't transform lightPos by gl_ModelViewMatrix

Just use lightPos.xyz in place of tfLightPos -- in fact you dodn't need tfLightPos at all

Answer 2

Sadly, this is impossible to fix without passing more information to the vertex shader. Since glTranslatef and glRotatef are used for the camera movements as well as the model movements, there is no way for the shader to distinguish between the two without passing the transformations and rotations to GLSL in vec3s.