texture image does not map correctly

Question

I am trying to map a texture image to a sphere.

I have vertices and texture coords in different vectors, that's why I am using glBufferSubData.

std::vector<glm::vec3> sphere_vertices;
std::vector<int> sphere_indices;
std::vector<glm::vec2> sphere_texcoords;

I don't use any colors , only vertices,indices,textures.

I am using:

// upload geometry to GPU
glBindVertexArray(sphere_VAO);
glGenBuffers(1, &sphere_vertices_VBO);
glBindBuffer(GL_ARRAY_BUFFER, sphere_vertices_VBO);


glBufferData(GL_ARRAY_BUFFER, sizeof(float) * sphere_vertices.size() + sizeof(float) * sphere_texcoords.size(),
            0, GL_STATIC_DRAW);

glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(float) * sphere_vertices.size(), sphere_vertices.data());

glBufferSubData(GL_ARRAY_BUFFER, sizeof(float) * sphere_vertices.size(), sizeof(float) * sphere_texcoords.size(), sphere_texcoords.data());

glGenBuffers(1, &sphere_indices_VBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, sphere_indices_VBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(int) * sphere_indices.size(), sphere_indices.data(), GL_STATIC_DRAW);


// setup vertex attributes
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);

// texture coords attrib
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float) , (void*)(sizeof(float) * sphere_vertices.size()));

and the image does not map correctly on the sphere.

The image I am receiving:

-- UPDATE ---

I used sphere_texcoords.push_back((glm::vec2((x + 1) / 2.0, (y + 1) / 2.0))); for texcoords and it works now!

Rabbid76 Rabbid76 · Accepted Answer · 2019-09-05T14:19:00

The size of the buffer and the buffer offsets have to be specified in bytes.
Note, the size of an element is sizeof(glm::vec3) respectively sizeof(glm::vec2) rather than sizeof(float):

size_t vertices_size  = sizeof(glm::vec3) * sphere_vertices.size();
size_t texcoords_size = sizeof(glm::vec2) * sphere_texcoords.size();

glBufferData(GL_ARRAY_BUFFER, vertices_size + texcoords_size, 0, GL_STATIC_DRAW);

glBufferSubData(GL_ARRAY_BUFFER, 0, vertices_size, sphere_vertices.data());

glBufferSubData(GL_ARRAY_BUFFER, vertices_size, texcoords_size, sphere_texcoords.data());

When named buffer object is bound the the last parameter of glVertexAttribPointer is treated as a byte offset into this buffer. The offset of the texture coordinates has to be:

glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(glm::vec2), (void*)vertices_size);

In general the size of the data of a std::vector<T> v in bytes can be get by:

size_t size = sizeof(T) * v.size();

respectively

size_t size = sizeof(*v.data()) * v.size();

texture image does not map correctly

1 Answers