c++ - OpenGL Vertexbuffer对象纹理坐标

我想用C++中的VBO创建网格类。
该类如下所示:

mesh::mesh(std::vector<Vector3d>* Vertices, std::vector<unsigned int>* Indices, std::vector<Vector2d>* TextureCoords) {
    if(Vertices) this->vertices = *Vertices;
    if(Indices) this->indices = *Indices;
    if(TextureCoords) this->textureCoords = *TextureCoords;
    chatbox.AddMessageToQueue("vertices.size() : %d", vertices.size());
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, vertices.size()*sizeof(Vector3d) + textureCoords.size()*sizeof(Vector2d), 0, GL_STATIC_DRAW);
    glBufferSubData(GL_ARRAY_BUFFER, 0, vertices.size()*sizeof(Vector3d), vertices.data());
    glBufferSubData(GL_ARRAY_BUFFER, vertices.size()*sizeof(Vector3d), textureCoords.size()*sizeof(Vector2d), textureCoords.data());

    glGenBuffers(1, &IND);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IND);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size()*sizeof(unsigned int), &indices[0], GL_STATIC_DRAW);
}

void mesh::draw() {
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    glVertexPointer(3, GL_FLOAT, 0, (void*)0);
    glTexCoordPointer(2, GL_FLOAT, 0, (void*)(sizeof(float)*3*6));

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IND);
    glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, (unsigned int*)0 + 0);

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}

问题仅在于纹理坐标。我试图像这样创建网格:

std::vector<unsigned int> indices;
std::vector<mesh::Vector3d> vertices;
std::vector<mesh::Vector2d> texCoords;

vertices.push_back({PosX, PosY, 1.0});
vertices.push_back({PosX + SizeX, PosY, 1.0});
vertices.push_back({PosX + SizeX, PosY + SizeY, 1.0});
vertices.push_back({PosX, PosY + SizeY, 1.0});

indices.push_back(0);
indices.push_back(1);
indices.push_back(2);

indices.push_back(0);
indices.push_back(2);
indices.push_back(3);

texCoords.push_back({0, 1});
texCoords.push_back({1, 0});
texCoords.push_back({0, 0});

texCoords.push_back({0, 1});
texCoords.push_back({1, 1});
texCoords.push_back({1, 0});

gui_checkbox = new mesh(&vertices, &indices, &texCoords);

但是结果是错误的，如您在下面的左图中看到的(右图是所需的):

顶点处于正交模式，因此顶点的坐标原点在左上角，而纹理坐标的原点在左下角，就像在OpenGL中一样。

最佳答案

当使用索引来寻址顶点位置时，纹理坐标也会被索引。在您的情况下，这意味着您仅使用texCoords中的前四个条目。奇怪的外观来自texCoords [0] == texCoords [3]。

正确的texCoords很可能是

texCoords.push_back({0, 1});
texCoords.push_back({1, 1});
texCoords.push_back({1, 0});
texCoords.push_back({0, 0});

这些可以从顶点坐标导出:每当其对应的顶点具有相同的分量值时，texCoords在一个分量处应具有相同的值。例如if vertices [0] .y == vertices [1] .y => texCoords [0] .y == texCoords [1] .y，依此类推。此外，必须翻转texCoords y坐标，因为顶点原点在左上角，而texcoords在左下角开始。

编辑:

glTexCoordPointer(2, GL_FLOAT, 0, (void*)(sizeof(float)*3*6));

在我看来不正确。该语句告诉我们，第一个纹理坐标在第六个vector3之后开始，但是它们不应该在第四个vector3之后开始吗？ (您在顶点中只有4个条目):

glTexCoordPointer(2, GL_FLOAT, 0, (void*)(sizeof(float)*3*4));