使用 ASSIMP 和 OpenGL 加載 3d 模型中的紋理不正確

Question

我正在嘗試通過使用 GLUT 而不是 WGL 來修改加載包含在 ASSIMP 示例代碼中的3d 模型的示例代碼。 但是，我遇到了紋理問題，如下圖所示：

雖然它應該如下圖所示：

以及用於繪制下面列出的 3d 模型的代碼：

void recursive_render (const struct aiScene *sc, const struct aiNode* nd, float scale){
unsigned int i;
unsigned int n=0, t;
struct aiMatrix4x4 m = nd->mTransformation;
m.Scaling(aiVector3D(scale, scale, scale), m);
// update transform
m.Transpose();
glPushMatrix();
glMultMatrixf((float*)&m);
// draw all meshes assigned to this node
for (; n < nd->mNumMeshes; ++n){
    const struct aiMesh* mesh = scene->mMeshes[nd->mMeshes[n]];
    apply_material(sc->mMaterials[mesh->mMaterialIndex]);
    if(mesh->mNormals == NULL){
        glDisable(GL_LIGHTING);
    }
    else {
        glEnable(GL_LIGHTING);
    }
    if(mesh->mColors[0] != NULL) {
        glEnable(GL_COLOR_MATERIAL);
    }
    else {
        glDisable(GL_COLOR_MATERIAL);
    }

    for (t = 0; t < mesh->mNumFaces; ++t) {
        const struct aiFace* face = &mesh->mFaces[t];
        GLenum face_mode;
        switch(face->mNumIndices) {
            case 1: face_mode = GL_POINTS; break;
            case 2: face_mode = GL_LINES; break;
            case 3: face_mode = GL_TRIANGLES; break;
            default: face_mode = GL_POLYGON; break;
        }
        glBegin(face_mode);
        for(i = 0; i < face->mNumIndices; i++){
            int vertexIndex = face->mIndices[i];    // get group index for current index
            if(mesh->mColors[0] != NULL)
                Color4f(&mesh->mColors[0][vertexIndex]); 
            if(mesh->mNormals != NULL)
                if(mesh->HasTextureCoords(0)){  
                    glTexCoord2f(mesh->mTextureCoords[0][vertexIndex].x, 1- mesh->mTextureCoords[0][vertexIndex].y);                    
                }
                glNormal3fv(&mesh->mNormals[vertexIndex].x);
                glVertex3fv(&mesh->mVertices[vertexIndex].x);
        }
        glEnd();
    }
}
// draw all children
for (n = 0; n < nd->mNumChildren; ++n)  {
    recursive_render(sc, nd->mChildren[n], scale);
}
glPopMatrix();

}

apply_material 函數，與 ASSIMP 提供的示例幾乎完全相同

void apply_material(const struct aiMaterial *mtl)
{
float c[4];
GLenum fill_mode;
int ret1, ret2;
struct aiColor4D diffuse;
struct aiColor4D specular;
struct aiColor4D ambient;
struct aiColor4D emission;
float shininess, strength;
int two_sided;
int wireframe;
unsigned int max;   // changed: to unsigned
int texIndex = 0;
aiString texPath;   //contains filename of texture
if(AI_SUCCESS == mtl->GetTexture(aiTextureType_DIFFUSE, texIndex, &texPath))    {
    unsigned int texId = textureIdMap[texPath.data];
    glBindTexture(GL_TEXTURE_2D, texId);
}

set_float4(c, 0.8f, 0.8f, 0.8f, 1.0f);
if(AI_SUCCESS == aiGetMaterialColor(mtl, AI_MATKEY_COLOR_DIFFUSE, &diffuse))
    color4_to_float4(&diffuse, c);
glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, c);
set_float4(c, 0.2f, 0.2f, 0.2f, 1.0f);
if(AI_SUCCESS == aiGetMaterialColor(mtl, AI_MATKEY_COLOR_AMBIENT, &ambient))
    color4_to_float4(&ambient, c);
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, c);
set_float4(c, 0.0f, 0.0f, 0.0f, 1.0f);
if(AI_SUCCESS == aiGetMaterialColor(mtl, AI_MATKEY_COLOR_SPECULAR, &specular))
    color4_to_float4(&specular, c);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, c);
set_float4(c, 0.0f, 0.0f, 0.0f, 1.0f);
if(AI_SUCCESS == aiGetMaterialColor(mtl, AI_MATKEY_COLOR_EMISSIVE, &emission)) 
    color4_to_float4(&emission, c);
glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, c);

max = 1;
ret1 = aiGetMaterialFloatArray(mtl, AI_MATKEY_SHININESS, &shininess, &max);
max = 1;
ret2 = aiGetMaterialFloatArray(mtl, AI_MATKEY_SHININESS_STRENGTH, &strength, &max);
if((ret1 == AI_SUCCESS) && (ret2 == AI_SUCCESS))
    glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, shininess * strength);
else {
    glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 0.0f);
    set_float4(c, 0.0f, 0.0f, 0.0f, 0.0f);
    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, c);
}

max = 1;
if(AI_SUCCESS == aiGetMaterialIntegerArray(mtl, AI_MATKEY_ENABLE_WIREFRAME, &wireframe, &max))
    fill_mode = wireframe ? GL_LINE : GL_FILL;
else
    fill_mode = GL_FILL;
glPolygonMode(GL_FRONT_AND_BACK, fill_mode);

max = 1;
if((AI_SUCCESS == aiGetMaterialIntegerArray(mtl, AI_MATKEY_TWOSIDED, &two_sided, &max)) && two_sided)
    glEnable(GL_CULL_FACE);
else
    glDisable(GL_CULL_FACE);
}

還有 loadGLtextures 函數，我不認為它與剔除強硬有關。

int LoadGLTextures(const aiScene* scene) {
ILboolean success;
/* initialization of DevIL */
ilInit(); 
/* scan scene's materials for textures */
for (unsigned int m=0; m<scene->mNumMaterials; ++m) {
    int texIndex = 0;
    aiString path;  // filename
    aiReturn texFound = scene->mMaterials[m]->GetTexture(aiTextureType_DIFFUSE, texIndex, &path);
    while (texFound == AI_SUCCESS) {
        //fill map with textures, OpenGL image ids set to 0
        textureIdMap[path.data] = 0; 
        // more textures?
        texIndex++;
        texFound = scene->mMaterials[m]->GetTexture(aiTextureType_DIFFUSE, texIndex, &path);
    }
}

int numTextures = textureIdMap.size();
/* create and fill array with DevIL texture ids */
ILuint* imageIds = new ILuint[numTextures];
ilGenImages(numTextures, imageIds); 
/* create and fill array with GL texture ids */
GLuint* textureIds = new GLuint[numTextures];
glGenTextures(numTextures, textureIds); /* Texture name generation */

/* get iterator */
std::map<std::string, GLuint>::iterator itr = textureIdMap.begin();
printf("TextureIDMap Begin %i\n", textureIdMap.begin());
int i=0;
for (; itr != textureIdMap.end(); ++i, ++itr) {
    //save IL image ID
    std::string filename = (*itr).first;  // get filename
    (*itr).second = textureIds[i];    // save texture id for filename in map
    printf("Texture loaded: %s\n",filename.c_str());
    printf("Texture ID Map End: %i\n",textureIdMap.end());
    ilBindImage(imageIds[i]); /* Binding of DevIL image name */
    ilEnable(IL_ORIGIN_SET);
    ilOriginFunc(IL_ORIGIN_LOWER_LEFT); 
    success = ilLoadImage((ILstring)filename.c_str());

    if (success) {
        /* Convert image to RGBA */
        ilConvertImage(IL_RGBA, IL_UNSIGNED_BYTE); 

        /* Create and load textures to OpenGL */
        glBindTexture(GL_TEXTURE_2D, textureIds[i]); 
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, ilGetInteger(IL_IMAGE_WIDTH),
            ilGetInteger(IL_IMAGE_HEIGHT), 0, GL_RGBA, GL_UNSIGNED_BYTE,
            ilGetData()); 
    }
    else 
        printf("Couldn't load Image: %s\n", filename.c_str());
}
/* Because we have already copied image data into texture data  we can release memory used by image. */
ilDeleteImages(numTextures, imageIds); 
//Cleanup
delete [] imageIds;
delete [] textureIds;
//return success;
return true;
}

Lighthouse 3D 給出了一個這樣做的例子，但是，目前我無法在我的程序中實現 GLSL 和 VAO。 有什么解決辦法嗎？ 提前致謝。

Answer 1

我找到了解決方法。 我使用以下代碼更改了如何在recursive_render函數中訪問紋理：

glTexCoord2f(mesh->mTextureCoords[0][vertexIndex].x,  mesh->mTextureCoords[0][vertexIndex].y);

代替：

glTexCoord2f(mesh->mTextureCoords[0][vertexIndex].x,  1-mesh->mTextureCoords[0][vertexIndex].y);

Answer 2

這不是紋理的問題。 您的問題來自背面剔除（至少看起來是這樣，因為您可以看到鴨子的內部）。 要么您的多邊形以錯誤的順序纏繞，要么您的背面剔除設置不正確。 如果您在設置背面剔除的位置發布代碼，我們可以確切地看到問題所在。

也有可能你的一些法線面向內（這也可能是多邊形纏繞造成的）。 這可以解釋為什么你的鴨子的喙是漆黑的。

Answer 3

我很確定問題是紋理正在沿 Y 軸“翻轉”。 這就是為什么你的“1-y”有效。 它可以通過在加載時沿 Y 翻轉紋理來修復。 雖然我還不確定為什么，因為今天才偶然發現這個問題。

Answer 4

我不確定這是否有幫助，但您可以在導入模型時翻轉 UV 坐標const aiScene* scene = importer.ReadFile(path, aiProcess_FlipUVs);