Opengl ES diffuse shader not working

问题

I'm implementing simple ray tracing for spheres in a fragment shader and I'm currently working on the function that computes color for a diffusely shaded sphere. Here is the code for the function:

vec3 shadeSphere(vec3 point, vec4 sphere, vec3 material) {
      vec3 color = vec3(1.,2.,3.);
      vec3 N = (point - sphere.xyz) / sphere.w;
      vec3 diffuse = max(dot(Ldir, N), 0.0);
      vec3 ambient = material/5;
      color = ambient   + Lrgb * diffuse *  max(0.0, N * Ldir);
      return color;
   }

I'm getting errors on the two lines where I'm using the max function. I got the code for the line where I'm assigning max(dot(Ldir,N),0.0) from the webgl cheat sheet which uses the function max(dot(ec_light_dir, ec_normal), 0.0); For some reason, my implementation is not working as I'm getting the error:

ERROR: 0:38: 'max' : no matching overloaded function found

What could be the problem with either of the these max functions I'm using?

回答1:

There's 2 max statements in your shader. It's the 2nd one that's the problem

max(0.0, N * LDir) makes no sense. N is a vec3. There's no version of max that takes max(float, vec3). There is a version of max that's max(vec3, float) so swap that to be

`max(N * LDir, 0.0)`

and it might work. Basically your shader is NOT an ES 2.0 shader. Maybe it's being used on a driver that is not spec compliant (ie, the driver has a bug). WebGL tries to follow the spec 100%

回答2:

The dot product is a scalar value not a vec3, you need to either store it in a float

float diffuse = max(dot(Ldir, N),0.0);

or initialize a vec3 with it

vec3 diffuse = vec3(max(dot(Ldir, N),0.0));

Same goes for the ambient term. Usually both diffuse and ambient terms are just scalars.

来源：https://stackoverflow.com/questions/32743068/opengl-es-diffuse-shader-not-working