Why is My Normal Mapping Not Working Correctly?

Normal Mapping: Common Issues and Resolution

Introduction

While implementing normal mapping may seem straightforward, it's not uncommon to encounter unexpected results. Here are some common issues and their potential solutions to help you achieve the desired effects.

Wrong Texture Coordinates

Ensure that the texture coordinates passed to the vertex shader are accurate. Verifying that the texture coordinates correspond to the model geometry can prevent many problems.

Lighting Calculations

Check if the lighting calculations in the fragment shader are correct. Incorrect lighting can lead to unexpected shading. Verify that the light direction and surface normal are computed correctly.

Tangent and Bitangent Generation

The tangent and bitangent vectors are crucial for normal mapping. Double-check your function for generating these vectors. The following code is a corrected version of the one you provided:

void getTangent(const glm::vec3 &v0, const glm::vec3 &v1, const glm::vec3 &v2,
const glm::vec2 &uv0, const glm::vec2 &uv1, const glm::vec2 &uv2,
std::vector<glm::vec3> &vTangents, std::vector<glm::vec3> &vBiangents)
{
    // Edges of the triangle : postion delta
    glm::vec3 deltaPos1 = v1 - v0;
    glm::vec3 deltaPos2 = v2 - v0;

    // UV delta
    glm::vec2 deltaUV1 = uv1 - uv0;
    glm::vec2 deltaUV2 = uv2 - uv0;

    float r = 1.0f / (deltaUV1.x * deltaUV2.y - deltaUV1.y * deltaUV2.x);

    // Compute the tangent vector
    glm::vec3 tangent = (deltaPos1 * deltaUV2.y - deltaPos2 * deltaUV1.y) * r;

    // Compute the bitangent vector
    glm::vec3 bitangent = (deltaPos2 * deltaUV1.x - deltaPos1 * deltaUV2.x) * r;

    // Push the tangent and bitangent vectors to their respective containers
    for (int i = 0; i < 3; i++) {
        vTangents.push_back(tangent);
        vBiangents.push_back(bitangent);
    }
}

Vertex Shader Transformation Matrix

Ensure that the vertex shader applies the correct transformation matrices (e.g., Model, View, Projection) in the appropriate sequence. Verify if the matrices are calculated and passed to the shader correctly.

Fragment Shader Lighting Model

Review your lighting model in the fragment shader. Ensure that the diffuse and specular shading calculations are implemented accurately. Consider adding a simple lighting model to confirm that the lighting is working.

Texture Loading

Inspect the texture loading and binding process to ensure that the correct textures are bound to the desired units. Verify that the diffuse map, normal map, and other required textures are loaded and binded correctly.

Texture Parameters

Ensure that the correct texture parameters (e.g., wrapping, filtering) are set for both the diffuse map and the normal map. Improper texture parameters can affect the appearance of the normal mapping.

Conclusion

Troubleshooting normal mapping issues requires a thorough review of various aspects of the implementation. By addressing the potential issues discussed above, you can resolve the problems you are encountering.

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