CODEWITHSUNDEEP
c++opengl
manatttta
manatttta

Reputation: 3124

OpenGL Draw only some indexes from vertex array

how can I only draw selected indices from vertex array in OpenGL?

For instance, I am drawing my vertices like points, with some variable m_pointCloud containing my point cloud vertices (points):

glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);

glPointSize(m_pointSize * point_scale);

glColorPointer(4, GL_UNSIGNED_BYTE,
    static_cast<GLsizei>(sizeof(DensePoint)), &((*m_pointCloud)[0].r));
// glNormalPointer(GL_FLOAT,
//  static_cast<GLsizei>(sizeof(DensePoint)), &((*m_pointCloud)[0].n_x));
glVertexPointer(3, GL_FLOAT,
    static_cast<GLsizei>(sizeof(DensePoint)), &((*m_pointCloud)[0].x));

glDrawArrays(GL_POINTS, 0, static_cast<GLsizei>(m_pointCloud->size()) - 1);

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);

But I have some std::vector<size_t> indices containing the indices from m_pointCloud that I want to draw. How is this done?

Upvotes: 1

Views: 979

Answers (1)

user2209008
user2209008

Reputation:

Instead of glDrawArrays, use glDrawElements.

For example:

std::vector<GLuint> indices;

// populate vertices

glDrawElements(GL_POINTS, indices.size(), GL_UNSIGNED_INT, reinterpret_cast<void*>(indices.data()));

Note also that you cannot use size_t as an index type as OpenGL only allows 8, 16 and 32-bit indices.

Upvotes: 3

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