handling obj file without normal

Question

I am trying to build an obj file loader and I have written code to read an obj file with face f with v/vt/vn - vertex, texture coordinate, and normal.

While going through the obj file, there are so many files without normal coordinates.

My shader code in Fragment shader is:

float lambertianFactor = clamp(dot(normal, lightDirectionNormalized), 0.0, 1.0);
vec3 diffuseTextureData = texture(diffuseSampler, v_texCord).rgb;
vec3 effectiveDiffuse = diffuseTextureData*diffuse*lambertianFactor*directionalLight;    
effectiveDiffuse = diffuseTextureData*diffuse*lambertianFactor;

for obj file without normal coordinate but with diffuse texture, how am I supposed to handle diffuse lighting?

Have you considered computing normal vectors on import, based on your vertex positions and triangle indices? — DMGregory, Jul 11 '21 at 13:51
thank you @DMGregory, I was clueless because no article and post is suggesting anything. Does this mean I need to learn from different sources? I am self-learning WebGL and computer graphics. Is there any source you suggest that will help me in times like this ? and thank you for saving me — Pravin Poudel, Jul 12 '21 at 04:43
This is my rendering with obj file with Normal !!! https://www.youtube.com/watch?v=UWCrGjsQq4c — Pravin Poudel, Jul 12 '21 at 04:44
If that solved your problem, then I'll mark this question as a duplicate of the one I linked. If you still need help, you can edit the question and we can re-open it, or you can post a new question. — DMGregory, Jul 12 '21 at 11:05
i think it will be a good lead to your answer through the post for another person who has no idea whether they need to generate a normal or create a workaround without normal data. Like me who had no idea whether to generate a normal or do another thing !!! — Pravin Poudel, Jul 12 '21 at 12:24

handling obj file without normal

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