how to adjust the transparency of a texture mesh?

[PengZai]

cv::Mat image = cv::imread("../figs/vis_ref_rgb_data.png");
auto texture = glk::create_texture(image);

auto front_shader_setting = guik::ShaderSetting(guik::ColorMode::TEXTURE_COLOR, transformation);
front_shader_setting.set_alpha(0.5f);

std::shared_ptrglk::Mesh sides_wire, front_tex;
make_camera_drawables(sides_wire, front_tex, 1.0f, 0.6f, 0.8f, texture);

viewer->update_drawable("front", front_tex, front_shader_setting);

void make_camera_drawables(std::shared_ptrglk::Mesh& sides_wire,
std::shared_ptrglk::Mesh& front_tex,
float w, float h, float z,
const std::shared_ptrglk::Texture& texture)
{
// ----- shared geometry (5 vertices: 4 corners + apex) -----
// std::vectorEigen::Vector3f vertices = {
// { w/2.f, h/2.f, z}, // 0
// {-w/2.f, h/2.f, z}, // 1
// {-w/2.f, -h/2.f, z}, // 2
// { w/2.f, -h/2.f, z}, // 3
// { 0.f, 0.f, 0.f} // 4 (apex)
// };

std::vector<Eigen::Vector3f> vertices = {
    {w / 2, -h / 2, z},
    { -w / 2, -h / 2, z},
    { -w / 2, h / 2, z},
    { w / 2, h / 2, z},
    {0,0,0}
};



std::vector<unsigned int> side_indices = {
    0,4,1,  1,4,2,  2,4,3,  3,4,0
};

// ----- sides: wireframe, no texcoords -----
sides_wire = std::make_shared<glk::Mesh>(
    vertices.data(),             sizeof(float)*3,   // positions
    nullptr,                     0,                 // normals (none)
    nullptr,                     0,                 // colors (none)
    nullptr,                     0,                 // texcoords (none)
    static_cast<int>(vertices.size()),
    side_indices.data(),
    static_cast<int>(side_indices.size()),
    /*wireframe=*/true
);

// ----- front: its own 4-vertex list + texcoords + texture -----
std::vector<Eigen::Vector3f> v_front = {
    vertices[0], 
    vertices[1], 
    vertices[2], 
    vertices[3]
};
std::vector<unsigned int> front_indices = { 
    0,2,1,
    0,3,2 
};

std::vector<Eigen::Vector4f> front_vertice_colors = {
  {1.0f, 1.0f, 1.0f, 1.0f},
  {1.0f, 1.0f, 1.0f, 1.0f},
  {1.0f, 1.0f, 1.0f, 1.0f},
  {1.0f, 1.0f, 1.0f, 1.0f}
};


// UVs for the front face (flip V if your image is upside-down)
std::vector<Eigen::Vector2f> uv_front = {
    {1.f, 0.f},  // for v_front[0]
    {0.f, 0.f},  // for v_front[1]
    {0.f, 1.f},  // for v_front[2]
    {1.f, 1.f}   // for v_front[3]
    // {0.0f, 0.0f},
    // {1.0f, 0.0f},
    // {1.0f, 1.0f},
    // {0.0f, 1.0f}
};

std::vector<Eigen::Vector3f> normals = {
    {0.f,0.f,1.f}
};


front_tex = std::make_shared<glk::Mesh>(
    v_front.data(),              sizeof(float)*3,
    normals.data(),    sizeof(float)*3,              // normals (optional)
    front_vertice_colors.data(),                     sizeof(float)*4,                 // colors (none)
    uv_front.data(),             sizeof(float)*2,   // texcoords
    static_cast<int>(v_front.size()),
    front_indices.data(),
    static_cast<int>(front_indices.size()),
    /*wireframe=*/false
);
front_tex->set_texture(texture);

}

I go through the source code , it looks like we can't control the color of texture. if I call set_alpha, that change the material_color...

how can I do to change the transparency of texture?

[koide3]

In TEXTURE_COLOR mode, alpha values are obtained from the texture data, and material alpha is ignored. You can make textured objects transparent by adjusting the alpha values of texture pixels.

[PengZai]

cv::Mat image = cv::imread("../figs/vis_ref_rgb_data.png");
auto texture = glk::create_texture(image);

so I have to set alpha value either on image or texture, I go through your code, I didn't find any set_alpha function on texture class. so I have to set alpha on cv::Mat image manually?