Why Isn't My OpenGL Normal Mapping Working?

Normal Mapping: A Misconfiguration

Despite your efforts to implement normal mapping in your OpenGL application, the results are far from satisfactory. This article delves into the potential causes of your problems.

The Vertex Shader and TBN Matrix

Your vertex shader is responsible for generating the tangent (T), bitangent (B), and normal (N) matrices (TBN). This information is crucial for normal mapping, as it defines the local coordinate system for each vertex.

In your TBN matrix calculation function, you compute the tangent and bitangent vectors from the UV coordinates provided for each triangle. However, it's important to verify the correctness of these calculations. You should ensure that the tangent is perpendicular to the bitangent and that both vectors are orthogonal to the normal.

The Fragment Shader and Normal Mapping

The fragment shader is where normal mapping takes place. In your shader, you correctly sample the normal map and convert its RGB values to a normal vector. However, the color calculation seems to be amiss. Specifically:

• Multiple Color Settings: You appear to be overwriting the output color multiple times within the fragment shader. This incorrect practice can lead to unexpected results.
• Intensity Addition Instead of Multiplication: Instead of adding the diffuse and specular intensities to the base color, you should be multiplying them. Adding intensities can result in unrealistic lighting effects.

Other Potential Issues

• Ensure you have enabled the necessary OpenGL extensions for normal mapping support.
• Inspect the compilation logs of your shaders; they often provide valuable error messages.
• Try a simpler implementation of normal mapping by focusing on the diffuse contribution first, then gradually adding the specular and ambient components.
• If all else fails, refer to established resources such as the OpenGL Red Book or online tutorials for more detailed guidance on normal mapping.

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